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Gaseous nitrogen transformations in a mature forest ecosystem Cushon, Geoffrey H. 1985

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GASEOUS  NITROGEN  TRANSFORMATIONS  IN  A  MATURE  FOREST  ECOSYSTEM  by  GEOFFREY  A  THESIS THE  SUBMITTED  H.  IN  REQUIREMENTS MASTER  CUSHON  PARTIAL FOR  OF  THE  FULFILMENT DEGREE  OF  SCIENCE  in THE  FACULTY  OF  GRADUATE  DEPARTMENT  OF  STUDIES  FORESTRY  We accept this thesis as conforming to the required standard  THE  UNIVERSITY  OF BRITISH  MARCH  ©  GEOFFREY  COLUMBIA  1985  H. C U S H O N , 1 9 8 5  OF  In  presenting  this  advanced degree Library agree  shall that  purposes  thesis  in  at the The  make  it  permission  It  is  available  extensive  may be granted by  representatives.  fulfilment  University of  freely for  partial  understood  that  reference  copying  OF  FORESTRY  The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date: M A R C H 1985  requirements  of  this  and  copying  or  study.  thesis  my Department  for financial gain shall not be allowed without  DEPARTMENT  the  for  an  British Columbia, I agree that the  for  the Head of  of  or by  publication  my written  for  of  I  further  scholarly his or this  permission.  her  thesis  Abstract In by  the  mature  forests,  gaseous  denitrification.  gains  and  Both  are  reduction  nitrogen  reactions of  nitrogen  and  organic  may  fixation  are  be  dominated  and  biological  affected  by  moisture  carbon and the availability  of  nitrogen.  Gaseous outputs,  due  coniferous mineral  of  transformations, asymbiotic  conditions, temperature, pH, supply mineral  losses  nitrogen to  biological  forest  soil,  inputs,  in  due  asymbiotic  denitrif ication  southwestern  decaying  to  wood,  were  British  foliage  nitrogen  quantified  for  Columbia. Forest  and  bark  were  fixation, a  floor  and  mature material,  incubated  in  an  atmosphere of 0.1 atm acetylene to allow the simultaneous measurement  of  N 0  by  2  production  free-living for  80% of  amounts and no of  of  by  bacteria  denitrifying and  a total nitrogen  denitrif ication  effectively  0.0  blue-green  annual were  indication of  input  fixed  nitrogen  were  kg  N  ha by  prevent  nitrogen  Joss  thereby  allowing  a  bacteria  slow  of  0 . 8 ' kg  fixation  a . - 1  activity  but  N  floor ha  reduction  material  It  is  accretion  of  input.  ii  other  nitrogen  by  for  and foliage  detected.  of  that  sinks  small  - 1  output  hypothesized  .accounted  a . ' Relatively  1  in bark was  gaseous  outcompeting  fixation and bulk precipitation  Forest  acetylene  in mineral s o i l , decaying w o o d  found, - 1  algae.  and  this  Traces  nitrogen  was  forest  may  mineral  nitrogen,  asymbiotic  nitrogen  Table of  Contents  Abstract  ii  List of Tables  v  List of Figures  vii  Acknowledgements  viii  1.  INTRODUCTION  1  2.  LITERATURE REVIEW  5  2.1 A s y m b i o t i c Nitrogen  Fixation  5  2.2 Denitrif ication 2.3 Environmental  6 Factors A f f e c t i n g ANF  and Denitrif ication  2.3.1 Soil Aeration and Moisture 2.3.2 Availability  of Organic  8  Carbon  10  2.3.3 Temperature  11 •  2.3.4 Soil Reaction  12  ;  2.3.5 Nitrogen  13  2.3.6 Other Mineral Nutrients  15  2.4 Denitrif ication and A s y m b i o t i c Nitrogen  Fixation in Forests  15  2.4.1 Denitrif ication  16  2.4.2 A s y m b i o t i c  17  2.5 The ,  8  Effects  of  Nitrogen Fixation Forest  Management  Nitrogen Fixation and Denitrif ication  Activity  on  Asymbiotic 19  3.  OUTLINE OF RESEARCH  22  4.  THE  23  5.  METHODS  31  5.1 Field Procedures  34  5.2 Lab A n a l y s i s  36  5.3 Calculations  37  STUDY AREA  5.4 Site Quantification  38 iii  6.  RESULTS AND DISCUSSION  41  6.1 Nitrogen Fixation  41  6.1.1 Forest Floor and Mineral S o i l  41  6.1.2 Decaying W o o d  43  6.1.3 Foliage  48  6.1.4 Bark  52  6.2 Denitrif ication  7.  ^..52-  6.3 Total Flux  56  6.4 Sources of Error  61  S U M M A R Y AND CONCLUSIONS  64  LITERATURE CITED .,  67  iv  List of  Tables  Table  1  Page  Mean monthly  temperature  the  average  20  year  and monthly  (last  year  precipitation  1975)  for  the  in  1984 and  UBC  Research  Forest, Marc Station 2  Volume, density  26  and biomass data  30m X 30m study  4  Regression  equations at  Bimonthly  strata  on  (12 noon) on sampling days  relating  breast  biomass  height  Source: M.C. Feller (unpublished 5  sample  nitrogen  fixation  of  (D),  foliage =  //7Y(kg)  32  (Y) a  to +  outside b/rtD(cm).  data) •  rates  and  39 total  annual  fixation  1984 Average  moisture content  7  Nitrogen  fixation rates (nmoles  N ha  - 1  a- ) 1  (by  in foliage  percent) of N g-  collected  1  day from  compared with foliage collected at ground 8  Bimonthly  denitrif ication  rates  and  total  sample material -  A s y m b i o t i c nitrogen  45  and total annual  flux  mature tree crowns  (A)  level (B)  51  1  annual  denitrif ication  1984 9  for 42  6  (kg  the 30  Air and soil temperature  diameter  the  site  3  bark  for  for 53  fixation rates in temperate forests  v  58  10  Nutrient  losses,  reserves  for  nutrient  logged  (A),  undisturbed (C) watersheds  inputs logged  in  precipitation and  slash  and  burned  in the UBC Research Forest  vi  nutrient (B)  and 60  .List of  Figures  Figure  Page  1  The nitrogen cycle  2  2  A c c e s s to the UBC Research Forest  24  3  Location of the study site  25  4  Diameter distribution of trees on the 30m X 30m sample plot  28  5  Nitrogen fixation rates in mineral soil and forest floor for  44  6  Nitrogen fixation rates in decaying w o o d for  7  Nitrogen fixation rates in foliage for  8  Total annual nitrogen flux by strata  vii  1984  1984  1984  47 50 ..57  Acknowledgements I  wish  Kimmins  and  course  of  to  express  especially  this  study.  with drafting work  on  my  appreciation  M.C. Feller Thanks  are  for also  figures.  viii  to  advice due  to  T.M.  Ballard,  and guidance Bernice  F.B.  Hoi I,  J.P.  throughout  the  Morosoff  for  help  1. INTRODUCTION "Nitrogen agronomic nitrogen  is  and  the  principal  forest  in crop  crops"  production  (Gordon  has  can be summarized in abstract this  model  fixation,  is  complex, it  there  are  c y c l e . These nitrogen(N ), 2  by  is  two  et  generated form by  factor  in  al.,  1979).  a huge  the  growth  The  body  and  of  far  of  to  means  entry  of  note  that  into  outside  the  (Kormondy,  1976). S i m i l a r l y , there  which nitrogen  global nitrogen  significance, biological  is returned  are  both of  literature' which  the nitrogen cycle (Figure  interesting  greater  of  significance  1). While  of  industrial  terrestrial  are electrochemical and photochemical fixation  microorganisms means  only  limiting  of  nitrogen  atmospheric  fixation  of  N  by  2  a limited number  of  to the atmosphere, thus balancing the  c y c l e . By far the most  important of  these processes  is the  bacterial reduction of nitrate, or biological denitrification (Knowles, 1982a). When nitrogen  nitrogen  fertilizers  lost  in  limiting  harvested  factor  stimulate forest  to  growth  growth  materials  in  forest  increase productivity  that may occur as a result of  (Marion,  1979;  soils,  (Spurr and Barnes, 1973;  fertilization is carried out to  a decline in fertility  Intensification to  the  usually  G e s s e l , 1959). Forest also to o f f s e t  is  Morrison  and  and  nutrients  Foster,  1979).  of utilization and the shortening of rotation ages in response  increased  fibre  demand  will  accentuate  the  potential  for  soil  impoverishment  (Kimmins, 1977). While nitrogen fertilizers are e f f e c t i v e , they  are  increasingly  expensive  'hard  cash'.  As  clear  that  becoming  pollution,  and  develops,  it  agriculture.  seems Biological  this d i l e m m a . The bacteria  and  nitrogen  possibility  waste  carbon  in  competition forestry fixation  of  terms  rank  offers  two  nitrogen  photosynthesis  1  fossil  industrially  will  producing or  for  of  a  lower  energy, fixed  exists  nitrogen  priority  approaches fertilizers  water  than  to  solving  using  cultured  and  is  being  2  Atmospheric nitrogen (N.  denitrifying bacteria (NO  Ammonia(NH ) and Nitrate (NO")  electrochemical and photochemical fixation  Nitrogen fixing organisms  3  Industrial fixation  birds and fish Shallow marine sediments assimilation and anabolism  Deep sediments  \  Producers Nitrate bacteria (NO  decay £n"d wastes  n e r b i v o r y  decay and wastes  Consumers  Amino acids urea, uric acid, organic residues  \ Nitrite bacteria (NH  Figure  Ammonifying bacteria  1. The nitrogen cycle. Adapted from: Kormondy, 1969.  3  investigated (Sprent, 1979). Biological nitrogen fixation may also be used as an ^alternative such  as  those  important us  that  to  chemical  involving  fertilizers. plants  in agriculture for  of  the  fixation  sustained  rice  production  throughout  suggested  that  biological  nitrogen  accumulated  by  Much to  research  enhance  significance  fixation  by  nitrogen  fixation  (Granhall  important  a  been  (1977) tells mainstay  studies  major  of have  source  of  (Roskoski, 1980;  nitrogen-fixing  Less  free-living  well  is  However,  when  process  also  small  the  when is  nitrogen  exists  (Hendrickson  is  Nitrogen  nitrogen  inputs of  1980). Evidence  decay  understood  generally  plant growth, even small  wood  symbioses  microorganisms.  (ANF)  fixation.  and Lindberg,  in the  of  productivity.  nitrogen  limiting nutrient factor for significant  have  the  succession  on the use  nitrogen  symbiotic  be  systems,  1975).  of  to  been  Ecosystem  may  during  forest  compared  (legumes),  has  ages.  fixation  preserve  asymbiotic  be  the  and  by  may  algae  biomass  has focused  accretion  be  Fabaceae  blue-green  in forest  Todd, Waide and Cornaby,  nitrogen-fixing  a long time (Nutman, 1975). Stewart  nitrogen  nitrogen  Symbiotic  and  that  the may ANF  Robinson,  1982). Any the  discussion  significance  of  of  biological  denitrif ication.  processes are linked, responding (Knowles, lipoferum,  nitrogen There  that  has the  on the conditions present Denitrif ication  can  capacity  is  in kind to  1978; Granhall, 1981). There to  fixation some  should  also  consider  evidence  that  the  two  the  site  the nitrogen  is one species of effect  both  status of bacteria,  Spirillum  transformations, depending  (Neyra et al., 1977). be  a  major  source  of  nitrogen  fertilizer  (Rolston, 1981), resulting in decreased fertilizer e f f i c i e n c y . Other reasons interest in denitrif ication include;  loss for  4 1.  its  potential  use  in  the  removal  of  nitrates  from  waste  water  (Schroeder, 1981) and other high-nitrogen waste materials. 2.  its  contribution  involved  in  the  (Knowles,  Our  knowledge  effect  prescribed study  was  significance  of  these  of  ANF  management  burning  and  undertaken ANF  (N 0)  to  2  reactions  the  which  biological  atmosphere where  result  and  nitrogen  and denitrification practices  fertilization with  review of the pertinent objectives  oxide  in  the  it  is  depletion  of  1982a).  roles  of  of  nitrous  stratospheric  ozone  incomplete. The  of  the  on  such them  main objective  denitrif ication  in  a  in forest  as are  transformations  ecosystems  harvesting, not  of  well  understood.  forest  and  scarification,  determining  mature  remains  the  This  relative  ecosystem.  A  literature was undertaken to determine more specific  and the best methods by .which these objectives  might be met.  2. LITERATURE REVIEW  2.1 A S Y M B I O T I C NITROGEN FIXATION Biological  nitrogen  ammonia of and  (NH ). Organisms 3  the kingdom Prokaryota cyanobacteria  (asymbiotically) bryophytes, of  fixation  or  in  floor, of  are  to and  generally  of  Jurgensen  variety  decaying  (Sprent,  the  of  be  by  forest  and  with  are  Of  as  all  certain  interest  (N )  eubacteria organisms  species  of  include  this  study  bacteria  has  been  fungi,  members  sp. Arctostaphylos  in  to  2  members  free-living  plants. These  such as Alnus  and  in  may  the be  phyllosphere. aerobic,  sp. and  are  free-living  rare  or  absent  1971).  from  Anaerobic  Clostridium (1971)  predominant  bacteria  the  Free-living  acidic,  that  fix  and  facultative  nitrogen-fixing  or  in  facultative bacteria  forest  soils  nitrogen  Robinson, anaerobe  bacterium  the  bacteria  nitrogen-fixing  generally  (Hendrickson  found  reported  anaerobic  and Robinson, 1982). Aerobic  isolated  are 1982).  Bacillus from  a  soils in North Carolina and Washington, and from Alaskan  tundra. Other bacteria known to fix nitrogen Bei jerinckia,  occur  association  free-living  nitrogen  Davey  nitrogen  algae.  genus  the  atmospheric  1979), and include species of  algae). They  1981).  Davey,  and to  be  this  1977) and higher  wood  (Hendrickson  (Jurgensen  polymyxa  fixation  fixing  thought  of  and non-legumes  (Cromack,  Nitrogen  anaerobic  transformation  cycads (Stewart,  sp.  capable  capable  symbiotic  bacteria and blue-green  forest  of  (blue-green  the Fabaceae  Ceanothus  is the reduction  Enterobacter,  Klebsiel  la,  include  Pseudomonas,  members of  the  Achromobacter,  genera Spirillum  Micrococcus.  Over  20  species  of  blue-green  nitrogen, all of which are members of  5  algae  have  the order  been  Nostocales  reported  to  (Jurgensen  fix and  6 Davey,  1970). Approximately  others with  one  third  of  these  are  found  in  soil  while  are found associated with certain bryophytes, cycads and ferns, and fungi  Davey  as  (1968)  blue-green suggest  that  (Hendrickson  investigated  algae  nitrogen cycle certain  lichens  in  the of  and  forest  some  soils  s o i l s , but  contribution  of  only  may  be  the  1982).  and  found  when  pH was  nitrogen-fixing  established forests  ecosystems  Robinson,  low  of  and  numbers  above  blue-green  is negligible. Of contribution  Jurgensen  of  5.4. They  algae  to  the  more significance in  nitrogen-fixing  lichens  (Denison, 1973; Millbank, 1978). The reduction of dinitrogen to a m m o n i a , N  2  + 3H —-2NH 2  is an exothermic reaction, but because of energy  is  adenosine  required  for  the  triphosphate  organism. The  reaction  (ATP)  reaction  is  to  which  3  the stability of the N  occur. This  energy  is' generated  by  by  oxygen  catalyzed  a highly  is  hydrolysis  molecule,  2  provided  by  within  the  sensitive  system  known as the nitrogenase enzyme complex. The reader is referred to (1979) for  a more thorough  discussion of  nitrogen  Sprent  fixation metabolism and  nitrogen fixation in general.  2.2 DENITRIFICATION Denitrif ication  may  denitrif ication  which  insignificant"  (Wollum  microbial  reduction  occur requires and  of  abiologically high  N0 " 2  Davey,  nitrate  and  1975).  (N0 ) 3  and  or  biologically.  low  pH  Biological nitrite  2  N0 -—^N0 -—-NO—-N 0—-N, 2  2  generally  denitrif ication  (NOf)  nitrogen oxides (NO, N 0 ) and atmospheric nitrogen; 3  is  "Abiological  to  the  low  and  is  the  gaseous  7 Denitrif ication where  anaerobic  essentially  aerobic, but  reduction  is  structure  of  result also  facultative  in nitrogen evolved  (nitrification)  in  organisms  that  the  involved  which  byproduct  may  be  a  and  aquatic  transformation  bacteria, that  loss and will not a  soil  The  of  utilize  nitrogen  reductions  is  the  fails  to  1977).  by  oxides  enter  the  Nitrate  cell  may  Nitrous  oxidation  contributor  as  1982a). The  also  to ammonia which do  microbial  significant  effected  nitrogen  be discussed further. of  environments  oxygen (Knowles,  (Alexander,  and dissimilatory  as  in  in the absence  dissimilatory, the  reported prevail.  acceptors  assimilatory  be  been  conditions  terminal electron  undergo  has  oxide  of  not can  ammonia  of  N 0  in  from  less  than  and  Al call genes  2  certain  s y s t e m s (Aulakh et al., 1982). The genera are  bacterial  (Bryan,  the  that  1981). Those  most  (Knowles,  species  commonly  can  from  in  come  the. genera  isolated  1982a). However,  denitrify  soil  and  Pseudomonas  may  be  of  greatest  s y s t e m s , Pseudomonas  thirty  significance  and  Achromobacter  may be the most significant (Focht, 1978). Denitrifying them to Most are end  reduce  possess N0  2  _  More  synthesize  successively all the  dependent.  product,  1982a).  bacteria  while  more  a  reduced  reductases, while Others  still  thorough  lack others  series  the  2  have  discussions  Knowles (1981,1982a) and Delwiche (1981).  oxides  lack the N G y  reductase  only  of  reductases  nitrogen  some  N 0  of  the  and  N 0 2  denitrif ication  that  (Knowles,  1981).  reductase, and  yield  N 0 2  reductase may  enable  be  as  the  (Knowles, found  in  8 2.3 ENVIRONMENTAL FACTORS Both  denitrif ication  affected  by  aeration  and  a number  temperature the two  and  and  soil  ANF  of  moisture  AFFECTING ANF AND are  reduction  environmental status,  pH. The  the  reactions  and  factors. These  availability  effects  DENITR1FICATION  of  soil  of  factors organic  inorganic  processes will be quite different. Few, if any  independent  of  factor  in  a  overall  rate of  successive  are  similarly  include  soil  carbon,  soil  nitrogen of  these  levels  on  factors  are  each other making it difficult to determine a r a t e - c o n t r o l l i n g  particular  system.  Environmental  denitrif ication but frequently  reductases  (Knowles,  factors  affect  not  only  the  exert differential effects on the  1981). In this way  the  relative  amounts  of  denitrif ication  as  the products that accumulate may be affected.  2.3.1 SOIL A E R A T I O N AND Soil  aeration  and  MOISTURE moisture  affect  ANF  and  they affect the presence of oxygen which inhibits both Nitrogen-fixing protective root  organisms  mechanisms  nodules  heterocysts  in  by  heterotrophic  against  symbiotic  blue-green  bacteria  have  oxygen,  including  nitrogen-fixing  activity  to  scavenge  0  2  and  keep  oxygen  is  required  for  the  production  nitrogen  most  al, only  1982). Other  When oxygen,  under  away  of  the  ATP,  as  Clostridium  of  barriers  (as  formation  of  slimes  uses  from  of  number  high  in some respiratory  nitrogenase.  many  As  bacteria  fix  (Silvester  et  sp., can  fix  nitrogen  to  nitrate  conditions.  denitrifying  oxygen will  it  the  microaerophilic conditions  organisms, such  under anaerobic  plants),  1981). Azotobacter  a  diffusion  algae and the formation  (Granhall,  effectively  developed  processes.  be  bacteria reduced  have rather  access than  nitrate  both (Bryan,  1981).  and The  /  9 N 0  reductase  low  concentrations  2  decline  but  is thought  the  of  to  be  0 ,  the  the  2  percentage  of  most  overall  N 0  sensitive rate  in the  2  of  end  to  0  and  2  under  denitrif ication  products  will  will  increase  (Focht, 1974). Denitrif ication fine-textured soils  of  (Allison,  soils  of  medium or 1965). The  has  been  poor  structure, poorly  fine  largely  texture  greatest  completely  water-saturated  be true of  forest  during  potential  soil  s o i l s , where  associated  (Rolston,  very  s o i l , and  normal  excessive  rainfall  drained  periods  for  with  of  denitrif ication would 1981), although  this  be  may  denitrif ication capacity is greatest  in not  while  the soil is drying f o l l o w i n g saturation (Binstock, 1984). Evidence occur  under  that  denitrif ication  apparently  (Fluehler  well-aerated  et  al., 1976) and ANF  conditions,  can  be  can  explained  by  the occurence of anaerobic microsites in aggregated s o i l s (Currie, 1961; Greenwood,  1961). Gaseous  inter-aggregate the  aggregate  pores  than  (Currie,  diffusion through  occurs  the  1961). Anaerobic  relatively  0  consumption diffusion  2  (respiration),  path  complicated by soils.  Smith  microsites  concentration  (Smith,  0  the variation  soils,  c o e f f i c i e n t s , respiration  need to  extend  in poorly  type  of  smaller may  through  the  pores  within  prevail  within  pores have drained.  depends  on  the  rates  of  0  the  diffusion  and  the  geometry  of  geometry  of  the  diffusion  path  in aggregate  diffusion  anaerobicity  2  attempted  aggregated  this  soil  1980). The  (1980) has  in  and  in  readily  conditions  the aggregate well after the inter-aggregate The  more  to  size within  model  considering rate  study  and to  the the  extent variation  aggregate  determine  most  the  aggregated s o i l s (Rolston, 1981).  2  is  aggregated  of  anaerobic in  gaseous  size. There  is a  development  of  10 Both ANF saturated  for  and denitrif ication are  long  precipitation.  Any  periods  of  activity  time  that  promoted  due  to  affects  in soils  structure,  these  that  remain  texture  and/or  factors  will  indirectly  affect ANF and denitrif ication.  2.3.2 A V A I L A B I L I T Y  OF ORGANIC  Photosynthetic algae,  depend  nitrogen-fixing  on  Consequently,  light  daily  nitrogen-fixing  and  acids  intensity  for  as  organisms  energy  and  carbon  is  abundant  wood  (Todd  al.,  common  combined  1975;  carbon  as  denitrif ication  a  bacteria  source is  of  largely  in  controlled  capacity  has  organic  Shaw,  1958)  and  Reddy  et  carbon  concentrations  of  N0 ~ 3  1981).  environments  where  in  Roskoski,  by  (NH , 4  1980;  +  3  Granhall  and  ratio.  and  require  anaerobic  the  (Burford been  supply  and  organic  conditions, of  readily  Bremner,  1975).  significantly  correlated  with  (Burford and Bremner, 1975; Bremner  mineralizable  al. (1982) found  carbohydrates,  ANF have been reported  Under  Denitrif ication  carbon  denitrif ication and  of  is  energy.  matter  variety  N0 ~)  heterotrophs  organic  water-soluble  and  (Granhall,  nitrogen  are  decomposable  a  compounds  high rates of  et  denitrifying  growth  including  Lindberg, 1980), which has a high carbon to nitrogen Most  production.  „  most  and  limiting. In f o r e s t s , relatively decaying  in  utilize  sources,  aromatic  fixation, in general, is  organic  ATP  fluctuations  ft  Nitrogen  blue-green  occur.  nitrogen-fixing  compounds  organic  organisms, such as the  seasonal  capacity w i l l  carbon  alcohols,  quality  and  Heterotrophic organic  CARBON  available  (Burford rates carbon  and to  be and  Bremner,  1975).  proportional suggested  and  to that  11 denitrif ication carbon.  is  Under  influenced some  by  the  conditions,  denitrif ication, indicating that  this  rate  of  carbon factor  mineralization addition  is not  may  rate  of  organic  not  affect  limiting  (Knowles,  1981). Denitrif ication rates will be largely carbon are  in the soil and its position  generally  matter have  higher  deposition, been  near  the  demonstraed  to  the amount  of  in the p r o f i l e . Denitrif ication rates  surface  mineralization  influenced by  (Knowles,  and  decrease  1981) where  incorporation significantly  occur. with  organic  ANF  rates  increasing  soil  diurnally  and  reports  that  depth (Baker and A t t i w i l l , 1984).  2.3.3  TEMPERATURE Rates  seasonally nitrogen  of in  ANF . and response  fixation occurs  nitrogen-fixing  denitrif ication  to  temperature.  at extremely  and photosynthesis  (Nommik,  temperatures, most exists  that  nitrogen growth  (Granhall, 1981).  1956; Bremner  and  Shaw,  was  reduced  that  of  temperature, than are general  for  increased with  spite  high and l o w  optimum range  (1980) found  In  organisms are mesophiles. Evidence  fixation can be affected more by  The  fluctuate  nitrate  denitrif ication is between 1958).  60 and 65°C.  Jacobsen  slowly  at  and  7°C.  Alexander  and  the  increasing temperature. Denitrif ication has been  rate  reported  at 4°C. in an anaerobic atmosphere (Limmer and S t e e l e , 1982) although Bailey  (1976) reported  that  denitrif ication was  completely  inhibited  at  5°C. The  indirect  denitrif ication  may  effects be  more  of  soil  important  temperature than  the  on  direct  ANF effects.  and In  12 marine sediments, little variation in denitrif ication rate with has  been  of  other  as  well  reported biological as  profile.  (Knowles,  the  Much  development  processes  movement  of of  1982a). Soil  the  such  of  effect  affects  mineralization  and  rate  nitrification  and  temperature  may  be  1981) and  the  availability  of  1956;  Delwiche  and  (Rolston,  oxygen  the  carbon, water of  anaerobiosis  as  temperature  temperature  in  the  soil  to  the  related  carbon and nitrate.  2.3.4 SOIL REACTION Optimum Bryan,  pH  for  denitrif ication  1976) and nitrogen  fixation  (Nommik,  (Granhall,  1981) is generally  around  at pH 7, can occur  over a  7. Nitrogen broad  pH  range.  Beijerinckia low  as  fixation, although Certain  4 (Granhall,  bacteria  (minimum  et  3.6)  reaction  al. and  rate  and  a  highly  significant  pH.  While  denitrif ication  pH  the  increase  other tend  the  abiological  of NO, N 0 , N  decrease  mole  fraction  of  these  reactions 2  of  and C H N 0 3  2  denitrif ication  seems to  reductases.  to  1974). Interpretation  2  reductase  2  Decreasing  the  overall  of  N 0 2  results  nitrite  at  (Knowles,  and  at pH as  nitrogen-fixing  in soils more acid than pH 6.  found soil  polymyxa  of  studied  pH, the N 0  concentration  abundance  (1980)  decreasing than  lower  {Bacillus  algae can fix nitrogen  1981). However, the  bacteria is generally  Muller  of  asymbiotic  sp.) and some blue-green  free-living  to  optimum  low  correlation  pH  and of  the  pH that  1982a).  soils  between  decreases  with to  increasing  denitrif ication  final  is complicated by low  pH  be more sensitive  rate  in  in  yield  product the one  low 0  2  but  (Focht,  occurence or  more  13 As and  with  temperature,  denitrif ication  may  availability  of  which  are  necessary  these  nutrients  decreasing 1977)  mineral  pH.  which  is  the  be  of  soil  significant.  Soil  pH  will  such  nitrogen  optimum  will  effects  nutrients for  Low  indirect  pH  at  also  have  as  fixation.  near  The  neutral  seems  an  phosphorus  to  important  pH  and  on  ANF  affect  the  molybdenum  availability  pH  inhibit  and  of  both  declines  with  nitrification  impact  on  (Armson,  denitrif ication  in  s y s t e m s where nitrate is r a t e - l i m i t i n g .  2.3.5 NITROGEN Nitrogen organic  carbon  limiting. changes of  It  is  fixation is  is  abundant  a  competitive  N  are  energy  good,  disadvantage  available to  in  combined process,  environments  nitrogen  promoted  (NH , 4  or  for  nitrogen-fixing carbon  fixers  them to  with  3  inhibited  organisms  heterotrophs  that  must use a considerable fix  nitrogen, leaving  where  N0 ")  +  inorganic nitrogen (Granhall, 1981). If  combined nitrogen. Nitrogen the  common  and  self-regulated  in the levels of  combined  most  is by  supplies  are  at  can  utilize  portion  less for  a  of  growth  (Sprent, 1979). Denitrif ication nitrate limiting  concentrations factor  rate-control levels  of  nitrification  as  (Rolston,  are  often  rates  of  1981). At  found  carbon low  to  be  independent  mineralization w i l l  be  concentrations, N0 ~ may  soluble  organic  the  matter  latter  normally  concentrations  cannot  occurs also  offers  in  occur  an  wrthout  undisturbed  affect  the  excellent  systems  proportions  and  (Keeney, of  the  the  high  environment  nitrate  of  exert  3  (Knowles, 1982a). While the forest s o i l , with relatively  denitrif ication,  Nitrate  rates  for little  1980). gaseous  14 products product is  evolved. is N 0  At  high  nitrate  concentrations,  (Nommik, 1956) while  2  at lower  the  predominant  concentrations, more  N  2  produced. The  that  occurence  nitrification  (Knowles, two  of  and  by  and  which  each  and drying  process  such  as  cycles  may  on occur  in  soil  also  Nitrification  may  occur  then  downward  at to  take place (Hendrickson, Nitrification, and by NH  4  +  competition  for  is added  the  nitrifiers  have  Edwards,  1979).  nitrogen N . 2  the same or of  consequently  NH  4  +  among  and  adjacent  may  Simultaneous  a soil  zone  alternate  also  for occur  interface,  nitrification  variable  of  and  conditions  anaerobic-aerobic  with  suggests  Nitrification  processes  and  moisture, content. profile  where  and  nitrate  denitrif ication  denitrif ication, may  heterotrophic  available C/N  and  processes  (1978)  appropriate  an  suggests  can  1981; Knowles, 1978).  ratio  advantage  denitrif ication  fixation. Nitrogenase  Denitrif ication  surface  an anaerobic  a competitive  Nitrification  of  in s o i l s  the  coupled  occur.  the  two  aggregates.  occur  2  in time, in response to  The  sides  N0 ~)  2  be  might  provide  1984).  opposite  denitrif ication may  moves  that  (N 0,  1977). Knowles  successively  (Binstock,  simultaneously,  may  Verstraete, coupling  denitrif ication may occur wetting  intermediates  denitrif ication  1978; Focht  ways  common  soil  NH  may  4  reduced  fixation  also  may  be  occur  microenvironments, or even  an organism able to catalyze both processes  "When and  the  supplies"(Johnson  +  has the ability to reduce  nitrogen  controlled  organisms.  is drastically for  be  coupled  and  with  N 0 as well  as  simultaneously  in  2  in the  (Knowles,  same 1978).  culture  15 2.3.6 OTHER MINERAL Lack  of  plant  growth,  ATP.  The  fixation  phosphorus because  both  nutrients  affects  phosphorus  availability  as  Other  NUTRIENTS  of  are  iron  is  and  components  thought  nitrogen  to  fixation  necessary  for  the  is  vital  molybdenum of  the  before  nitrogenase  stimulate  nitrogen  it  affects  synthesis for  of  nitrogen  enzyme  system.  fixation  include  magnesium, boron, cobalt, copper and zinc (Granhall, 1981). Copper, denitrif ication.  molybdenum Magnesium  and  is  magnesium  necessary  for  are  all  required  growth, while  for  molybdenum  is an integral part of all the nitrate reductases that have been studied. Copper others  is  involved  in  the  reductase  in  some  organisms  while  in  it is required for reductase synthesis. Iron and sulphur are both  necessary for activity Sulphur Sulphide 1982a).  compounds  appears Sulphide  (discussed  of the denitrif ication enzymes (Bryan, .1981).  to  inhibit  can  in methods  have  several  the  also  NO  cause  section)  of  effects  and  N 0  relief  of  2  the N 0  on  denitrif ication.  reductases  (Knowles,  acetylene  inhibition  reductase which  2  may  have  consequences for the use of this technique in measuring denitrif ication.  2.4 DENITRIFICATION AND A S Y M B I O T I C NITROGEN FIXATION IN  FORESTS  The  the lack  of  of  the  study  ideal  of  both ANF and denitrif ication has been limited by  methods  acetylene-reduction method  of  information  for  assay  measuring on  acetylene-reduction  quantifying as  an  nitrogen  nitrogen assay  easy,  The  sensitive  fixation  fixation has  fluxes.  has  and  relatively  facilitated  (Hardy  advantages  development  over  et  al.,  other  inexpensive  a vast  increase  1973).  While  techniques, it  can  criticized on a number of grounds which w i l l be discussed in Methods.  in the be  16 A universal more been  elusive  method for the measurement of  (Focht,  estimated  by  1978;"" Rolston,  balance  from  Likens, 1979) and is the subject  2.4.1  nitrogen of  Denitrif ication cycle  studies  has (e.g.  most Bormann  and  forests,  ANF  losses  by  much speculation.  more  (1981) than  has  suggested  compensate  that  for  in  temperate  generally  small  denitrif ication, resulting in s l o w accumulation of combined Todd  et  denitrif ication allow  their  provided  al. in  (1975)  results  valuable  to  forests.  be  total  because of the greater  flux  of  mass of  as  studies  analytical  potentials  potential  rates  in decaying  nitrogen  nitrogen.  few  their  soil where  s o i l . Of  the  rate  the  found  10 c m . of  of  Although  about  potential was  Highest  one  considered  information  and in the upper  maximum.  provided  temperate  substrates. Highest floor  often  DENITRIFICATION Granhall  will  1981).  denitrif ication has proven  only, in  floor  Melillo successional  et  al.  suggested  that  following  clearcutting.  well-drained occurred  in  different  occurred  from  forest is at a  the  soil  less significance, in terms floor  of and  itself.  sequence  denitrif ication  they  logs on the  denitrif ication capacity, were decaying branches on the forest the forest  methods  available carbon  gas  of  (1983) in  organic  denitrif ication  in  forest  conditions. pulses  considered and  potential  denitrif ication  mineral is  soil  greater  Their  results  indicated  soils,  in  of  The  following  spite  authors hydrologic  low  the  speculated events  horizons.  in  pH  and major rainstorms. This agrees with the findings  young  that as  to  a They  stands  potential  (3.5  such  over  for  3.9)  and  denitrif ication spring  runoff  of Binstock  (1984)  17 who  demonstrated  greatest  while  that  the  denitrif ication  soil  (1983)  also  found  a  nitrate  concentration.  is  drying  strong  capacity  following  correlation  In forest  soils  in  saturation.  between  where  forest  soils  Mel i I lo  et  denitrif ication  nitrification  rates  is al.  and  are  low,  more information exists concerning the role of  ANF  nitrate may be the r a t e - l i m i t i n g factor for denitrif ication.  2.4.2 A S Y M B I O T I C NITROGEN Considerably in  forests, although  temperate  regions  vegetation  and  the  picture  have  soil  FIXATION  is  still  relatively  (Granhall,  closed  small  20 kg Nitrogen  losses  of  ha-  nitrogen  1  a  caused  cycles  inputs  and  by  in  between  outputs  may (Todd  indicates that ANF "can account  which'will  - 1  forests  in the forest nitrogen cycle  et al., 1975). A survey of the literature 1 to  nitrogen  1981). Gaseous  dominate the total gains and losses  for  incomplete. Climax  compensate  leaching  and  for  generally  denitrif ication,  and  ecosystems  may  may yield some accretion (Granhall, 1981). Paul  (1978)  account  for  annually  between  fixed  a  - 1  kg N  occurring in  to  that  per  cent  vegetation  and  seem  ANF of  the  -1  application  relatively  as s l o w l y to  high rates of  heterotrophic  N  amount the  rotation  available  of  nitrogen  amounts must  of  consider  cycled nitrogen that  is almost equal to  fertilizer. This  fertilizer  has  the  nitrogen  applications  which  advantage  2  one of  (Granhall, 1981) are  subject  to  leaching and denitrif ication.  nitrogen bacteria  climax  s m a l l , one  released, easily  broadcast  Asymbiotic  of  in  s o i l . While  accrued over a 90 year  - 1  ha  contrast  potentially  by  10  asymbiotically  kg N h a 200  5  suggests  fixation in the  in forests  soil  is  and forest  carried  out  primarily  f l o o r . Other  potential  18 sources  include  bacteria  and nitrogen-fixing  in  decaying  epiphytes  wood  and  on  forests  nitrogen-fixing  potentials of  carbon  was  supply  were  decaying  and  layer.  Todd  humus  rates  of  largest  nitrogen amount  fixation  of  greater mass of The  different  organic  occured  nitrogen  Jones  attention  on  nitrogen  fixation.  Subsequent  (Granhall  and  Douglas-fir  Lindberg,  could  fix  algae  in  leaf  negligible. The  in  rhizosphere  while  wood  considerable  coniferous  foliage  research  1980; Caldwell,  a significant  species on  that  occurred  Todd et al., 1978) failed to support  fixation  nitrogen-fixing  layer, and the  the  and  the  highest  humus, the  soil  (1970) that n i t r o g e n - f i x i n g  focused  forest  litter  imp.ortant  in decaying  fixation  of  be  most  importance of  due  to  the  bacteria on  leaf  soil.  report by  not  strata. The  al. (1975) reported  surfaces  may  nitrogen fixation data relative  w o o d , the  et  and the  in Sweden. Their data indicate the  emphasized, as the  components  surfaces,  living on bark, branches, foliage  forest f l o o r . Granhall and Lindberg (1980) present for three coniferous  foliage  Minnesota surfaces  presence of  component  source  may  of  and  potential  Jones  Hagedorn  nitrogen Oregon  (1982) and  nitrogen,  source and  (Sucoff,  with  was  others  foliage  a study  1979),  considered  a significant  of  nitrogen  a nitrogen-fixing  phyllosphere  of  Denison, 1979;  fixation. In  epiphytes  epiphytes the  by  a  of  this finding, indicating that  without  make  as  quantities  to  be  blue-green source  of  nitrogen fixation (Denison, 1973; Millbank, 1978). Roskoski  (1980) investigated  the northeastern youngest rates  and  stands larger  United  nitrogen  States. Fixation was  studied,  as  quantities  a of  result wood  of  fixation  in w o o d  highest  in the oldest  higher  litter.  The  acetylene higher  litter  in and  reduction acetylene  19 reduction logs  rates  which  because  were  provide  of  their  attributed  to  a  suitable  more  higher  moisture  anaerobic microsites. ANF  because of that  wood  content  nitrogen-fixing decay  the  and  material  ratio of may  the  help  fungi  will  in  bacteria will and  wood  perhaps  decay  large  nitrogen  their  dead  fixation  ability  forests  material. It  facilitate  benefit benefit from  respiration. Research indicates that in  for  to  process,  from from  retain  0  nitro.gen  fixation  not  part  suggested of  woody  nitrogen  carbon-rich 2  in  (1975) postulated  added  the  slow,  decay  reduced  although  is  has been  the  (Cornaby and Waide, 1973). Jorgensen  decay  wood  fixation  habitat  of  1979) was found to be insignificant.  woody  the high C/N  nitrogen  substrates  of  abundance  in the mineral soil in these (Roskoski, 1980)  and similiar sites (Tjepkema, Decomposition  a greater  levels  as  while  products  due  may  that  to  be  of  fungal  important  important  as  other  sources of nitrogen, such as crown wash (Larsen et al., 1982; Silvester et al., 1982).  2.5  THE  EFFECTS  OF  FOREST  MANAGEMENT  ACTIVITY  ON  ASYMBIOTIC  NITROGEN FIXATION AND DENITRIF I C A T I O N The  impact  has  received  practices  on  clearcutting, will  alter  of  forest  management  considerably  less  the  and  physical  scarification  chemical and  and  attention chemical  fertilization  physical  temperature, aeration, pH, bulk  practices  soil  density  on  than  soil the  properties are  biological effects of  examples  properties  such  soil. of  as  of  processes the  same  Forest  fires,  treatments moisture  and available nutrients  al., 1979) causing changes in rates of A N F and denitrif ication.  that  content,  (Jurgensen et  20  ANF  Site changes resulting from timber harvesting  should tend to  promote  and  generally  increase  soil  pH  season, and cause  increased  soil  saturation  the  anaerobic  denitrif ication.  temperature due  to  during  removal  processes  of  conditions putting  growing  vegetation.  promote  organisms  presence of  These  in  a flush  conditions  is a natural  of  at  a  competitive  occurence  will  favour  will also promote  carbon  denitrif ication, but  high mineral nitrogen  Fire  will  and denitrif ication. Logging  resulting  will  the  of  ANF  mineralization,  the  Logging  and  may  mineral  more  inhibit  for  L.)  in ANF  stands  in  temperature, These  following  soil  conditions  in many  (Knowles,  They  moisture,  pH,  will  promote  also  temperate  burning  forests  in loblolly  attributed  available  this  to  and  fire  will  increased  the  and has  activity  of  pine  been  significant  (P/nus  taeda  in  available  soil  carbon.  denitrifying  may  increase  improve  any change  bacteria  conditions  nitrate  for  nitrification  concentrations  denitrif ication. Rolston  in soil nitrate  in  (1981) reviewed  the  the  soil,  and  literature  on  losses of  cent  considerably  applied  conditions.  nitrogen  Fertilizer  fertilizer.  applications  This  may  will  vary  potentially  inhibit  Francis  (1982) studied  nitrification, nitrogen increasing  the  effects  of  soil  acidity  fixation and denitrif ication in forest  acidification  of  forest  soils  by  acid  on  nitrogen in  nitrogen  0 to 75 per  nitrogen  This should be considered when evaluating the net benefits of  levels.  resulting  loss after fertilization on cropped soils and reported  that  in  1982a).  fertilizers  of  by  increases  nutrients' and  the  Denitrif ication w i l l be influenced by Logging  ANF  availability (Sprent, 1979).  prescribed  South . Carolina.  These  carbon  used as a management t o o l . Jorgensen and Wells (1971) reported increases  rapid  nitrogen.  conceivably  disadvantage  and  with  soil  fixation.  fertilization. mineralization,  s o i l . He  precipitation  suggested will  lead  21 to significant reductions The an  removal  "ecosystem  fertilizers.  of  in these microbial processes.  vegetation  need". This  The  use  of  and the nutrients contained therein, creates  need  may  fertilizers  may  ecological reasons. The addition of in  other  plant  nutrients,  and  cycling of organic  matter by  reduction  nitrogen  soil  in  total  fertility  would  be  filled  be  by  unsuitable  nitrogen fertilizers  may  also  the  cause  use for  imbalances  organic  be decreased, even  matter if  content,  a continuous  chemical  economic  may create  changing the C/N ratio. "This and  of  in  and  defiencies the  natural  could lead to a  so  that  supply  long-term  of  fertilizer  were maintained" (Granhall, 1981). Clearly, role  in  a better  forests,  productivity  are  is to  must be considered.  be  understanding needed.  If  used, the  of  ANF  artificial long  term  and  denitrif ication, and  means  for  effects  on  promoting the  nitrogen  their forest cycle  3. OUTLINE OF In the  fall  of  1983 a study  RESEARCH  was  begun, with  the specific  objectives  of: 1.  quantifying from,  the net  a  mature  balance forest  between  gaseous  ecosystem  N inputs  and  to, and  determining  the  outputs relative  significance of the processes contributing to this balance. 2.  determining processes  where occur  at which they 3.  studying Based  the  and the  ecosystem relative  inputs and outputs on  the  gaseous  significance  of  N  transformation  substrate  to the  rate  occur.  the  investigation  in  Foliage  and  bark .of  activity  and  forest  were  in  the  in relation to season.  preceeding summer three  floor,  of  litrature  review  1983, 11  strata  tree  species  mineral  soil  were and  and were  sampled  3 classes  some chosen for of  preliminary for  study.  nitrogen-fixing decaying  wood  sampled for ANF and denitrif ication. The  description  ensuing  report  of the study  on  the  results  of  area, a discussion of  the results and their significance.  22  this  study  methods  will  include  a  and a discussion  of  4. THE The north  University  of  Haney,  British Columbia  British  Vancouver,  B.C.  Faculty  Forestry,  of  of  STUDY  AREA Research Forest  Columbia, Canada,  (Figure  2).  UBC,  The as  5,151  an  approximately  hectare  forest  experimental,  research  It contained established forest by  management activity  Its  proximity  2.  to  UBC  3.  A  large amount of  parts of the The  site  Forest  chosen  from  the  for  analysis  study  is in the southern  2.5 k m . northwest Forest  Valley  lies  to  the  Coast  inland  relief  and the  foothills  common winters, heavy  ie a  equable maritime  cloudiness cool  and  and  location  and  monthly  monthly temperature weather  in  (marine) climate a  relatively  precipitation, most  temperature  minimized  1984 was  of  small dry which  portion  of  which  travel  for  in the  various  range  of  summers, occurs  precipitation  for  warmer  23  the  transition  lower  and modified  by The  climatic c l a s s i f i c a t i o n as  Cfb  humid by  mild  Fraser  to  long  rainy.  This  temperatures wet  frost-free  period,  and  1984 and 20 year  average  wetter  with mild  Mean  and slightly  is  and  during the winter.  and monthly precipitation are presented slightly  (Figure 3).  climate, in general, is  temperatures, a  Research  Valley.  mesothermal characterized  the  mark  Ocean to the west  climate has been classified using the Koppen  as  disturbed  study. done  Mountains. The  mountainous  described  because-  of the main entrance  in the  the Pacific  1976),  was  the  demonstration  mensurational and ecological data exist  mesothermal, influenced by  (Klinka,  and  by  sample material.  this  Research Fraser  managed  of  forest.  approximately The  the  k m . east  that would not be  during the course of the where  time and handling of  ecosystems  located 7 km.  40  is  facility. It was chosen to be the location of this study 1.  is  in Table  than the  monthly mean 1. The 20 year  Figure 2. A c c e s s to the UBC Research  Forest.  Figure  3. Location  of  the s t u d y  site.  Table  1.  Mean  monthly  Research  temperature  Forest,  Marc  Mean Month  20  yr  and  Daily  Average  monthly  precipitation  in  20  yr  1984  and  the  20  year  average  (last  year  1975)  for  the  Station. Max.  T.("  Mean  C)  1984  Daily  Average  Min.  T.  (  Monthly  C)  1984  Average  Precip.(mm) 1984  J  3.9  7.1  -1.6  1.9  289  432  F  6.6  9 2  0.2  3.8  219  217  M  8.4  12.7  0.8  3.3  231  219  A  12.4  13.9  3.3  3.0  154  186  M  16.8  15.0  6.6  5.5  1 11  21 1  J  19.4  18.1  9.4  9.3  92  133  J  22.6  23.4  10.9  10.9  68  21  A  21.9  22.5  10.9  1 1.0  80  64  S  19.2  18.5  8.8  8.4  128  1 16  0  13.2  1 1.9  5.6  4.5  244  252  N  8.0  7.8  1.8  2.3  275  368  2.6  315  216  2206  2 4 3 5  D  5.3  3.2  0.0  Yearly  Total  UBC  27  average. The featuring The  southern flat  entire  to  part  gently  area  is  till soil  underlying  reworked  the  ablation  the  study till  by  evolved  recent  are  forest terrain  underlain  most  and colluvium  the  rolling  quartzdiorite. S o i l s have glaciation, the  of  study  a southwest  occuring  predominant is  overlying  var.  in the forest  varying  mixtures  menziesii),  western  western redcedar  {Thuja plicata  Research Forest  lies  in  a  granitic-cored  intrusive  some  parent  a mini  rock,  basal  till.  years  materials  It  is  pleistocene ago. Glacial  (Klinka, 1976).  Podzol  a sandy  overlain by  uplands.  predominantly  left by  10,000  Humo-Ferric  The  derived  loam  a 5 cm thick  from  in  texture  mor  humus  230 to 235 m asl with  transition  by  is dominated by temperate marine coniferous of  Douglas-fir  hemlock Donn). A  between plant  natural  synsystematic by  his  menziesii  u  (Mirb.)  (Raf.) Sarg.)  and  c l a s s i f i c a t i o n of  the  Klinka (1976). The  study  site  Moss(Po/ystichum)-\NRC-\NH  associations.  regeneration  (Pseudotsuga  (Tsuga heterophylla  has been carried out  Moss-Mahonia-DF-WH developed  a few  physiography,  aspect and average slope of 5%.  f o r e s t s , with  UBC  submontane  site is located at an elevation of  Vegetation  Franco  with  igneous  with 2 0 - 3 0 % coarse fragment content layer. The  a  from surficial deposits  event  site  has  The  following  vegetation a  wildfire  and  present in  had  1868.  The  overstory  was dominated by D o u g l a s - f i r while western hemlock and western  redcedar  occupied  distribution well 2  tree  in  the  diameters for  lower the  covered  Mahonia  approximately  nervosa  species  Pursh  present  with  2 5 % of lesser  tree  study  developed and higher shrubs were  m.)  Other  of  places  the  Figure  site. The  absent. The  amounts  included Vaccinium  layer.  area of  parvifolium  shrub  lower and  4  layer was  shrub  was  Gaultheria  presents  layer  S m i t h , Acer  not  (0 to  dominated shallon  a  by  Pursh. circinatum  28  JO  E H 3  Legend E 3 W « s l a r n R«dc«dar  •i W . , l . r H.mlocl< O Douglaa-fir n  to  30  40  50  60  70  BO  90  Diameter Class (cm.)  Figure 4. Diameter distribution of trees in the 30m X 30m sample plot.  29 Pursh, Tsuga heterophylla covering the  1 to  major  Trillium  2% of  and Rosa nutkana Presl. The the  ground with  species. Other ovatum  Stokesiella  herb  species  Pursh, Trientalis  oregana  (Sull.)Robins.  (Kindb.)Koponen  Hylocomium  splendens  munitum  included Dryopteris  /at/folia  Hook,  dominated  30% of the area, with Plagiothecium glabrescens  Polystichum  herb layer was sparse  a  moss  undulatum  common  and  (Kaulf.)Presl assimilis  Tiarella  layer  on  decaying  covering  loreus  L.  roughly  Rhizomnium  woody  (Hedw.)B.S.G. and Rhytidiadelphus  Walker,  trifoliata  (Hedw.)B.S.G. and  as  material.  (Hedw.)Warnst.  were also present. Biomass data for the 30m. X 2. The this  phyllosphere  species  was  amounting  30m. study  site are presented in Table  dominated by  Douglas-fir(DFF),  to  compared  1,140  kg  to  foliage biomass of  800  kg  for  western  redcedar(WRCF) and western hemlock(WHF) combined. Two decaying  species,  wood  on  Douglas-fir the  study  and  western  site. These  redcedar,  occur  comprised  as deadfall on the  the forest  floor and as standing stumps and snags. D o u g l a s - f i r w o o d was divided two  classes  corresponded as  of to  decay  agent  kg  of  The  was  to  the  two  biomass,  first,  stage  corresponded  (Schwartz:Fr.)Karst. 9,700  The  an incipient  Ved-rot'(RDF),  primary  decay.  of  wood  to  as  decay. The  an advanced stage brown  classes  in  referred  crumbly  of  roughly  rot,  Douglas-fir equal  of  into  'white-rot'(WDF), other, referred wood  decay.  Fomitopsis wood  proportions,  to The  pinicola  accounted  for  while  western  having  medium  redcedar(WRCW) accounted for 3,000 kg. Klinka  (1976) describes  productivity, but being, well  sites  such  suited for  as  forestry  this  one  as  use and suggests  should be intensively managed as commercial forests.  that  they  Table  2.  Volume,  density  density  is  '  soil  relative  measurements  sample  DENSITY(g  strata  cm')'  on  the  3 0 m  DRY  X  3 0 m  study  WEIGHT(kg)  site.  DRY  WEIGHT/HA(kg)  45  0.29  13,050  145,000  0.59  159.840  1.776.000  RDF  24  0.19  4,565  50,668  18  0.29  5,289  58,768  12  0.26  3.065  34.050  ,140  12,670  W R C  481  5,339  W H  322  3.580  Foliage  symbols  the  270  W R C W  stratum  for  LFH  W D F  1  data  SOIL' W o o d  1  biomass  VOLUME(m')  STRATUM'  Decayed  and  DF  are  explained  density are  for  for the  on  page  wood top  and 30  29  of  LFH cm  the and  of  text. bulk  mineral  density  for  soil  soil.  CO  o  5. METHODS Gaseous  nitrogen  fluxes  were  quantified  for  a  30m  plot in the UBC Research Forest. The plot was divided ability  to  reference in the for and  fix  nitrogen  and/or  denitrify.  to the available literature  summer  one  year  soil  of  and to  1983. Denitrif ication  beginning  The  on  representative  was  some preliminary  and  ANF  were  sampling  30m  square  into strata based on  stratification  in January,1984 and finishing  temperatures  X  done  with  sampling  done  measured  bimonthly  in November,1984. Air days  are  presented  was  done  in  Table 3. Measurement  of  gaseous  nitrogen  acetylene(C H )-ethylene(C H ) assay 2  and  the  1977).  2  2  acetylene  These  inhibition  can  be  for  4  done  fluxes  nitrogen  method  for  fixation  limiting  the  (Hardy et al., 1973)  denitrif ication  simultaneously,  using  (Yoshinari  the  amount  et of  al., field  sampling. Nitrogen-fixing proportional  organisms  to that at which N N  transform  This  suggests  a  conversion  ethylene  a  number  at  a rate  3  +  2  2  to  is reduced to NH :  2  C H  acetylene  2  3H —-2NH 2  + H  ratio  2  of  3  ~-C H 2  4  3 : 1 , but  for  of  reasons  "empirically determined ratios seldom equal the theoretical" (Roskoski, 1981; Rice and Paul, 1971). These reasons  include;  1.  w a t e r - s o l u b l e ' as  C H 2  2  is  roughly  65 times  saturate the nitrogenase 2.  Oxygen, which during long  3.  As  ethylene  as  is  system more than would N  is required for the production  N . 2  2  Hence,  it  may  (Knowles, 1982b).  of A T P , may be  depleted  incubations. is  not  inhibit physiological  involved  in  processes.  31  m e t a b o l i s m , nitrogen  deficiency  may  Table  3. Air and soil temperature  (12 noon) on sampling days.  Air T e m p ( ° C ) Jan 25 Mar 6 May 8 ' Jul 4 Sep 12 Nov 6 (  2 12 10 17 11 9  Soil Temp(°C) 4 5 7 n  11 6  33 The  effects  of  these  factors  material, such as forest relatively in  long  nitrogen will  times  cause  conditions. acetylene  overestimates of  significant  nitrogen-fixing 1979). In  diffusion  of  calibrating  Silvester and  et  nitrogen  incubated  hours  low  (Sprent,  nitrogen  may  and  the  (1982)  situations, such limiting  rates.  This  stoichiometric  rates of ANF encountered  In  this  conversion  in this study  ratio  an  of  acetylene  illustrates  the  specific  relationship  between  coniferous  study  for  for  wood,  increase with time, but averaged 7 hours.  of  assay  the  as  factor  solubility  reduction  decaying  investigating  activity, necessitating  the  investigated  in  when  some  be  fixation  acetylene  reduction  less than  the  nitrogen  al.  ratio was found to  were  most  fixation (Rice and Paul, 1971) and the higher  importance  The  soil,  be  s o i l , with  incubation  waterlogged  will  using  3.5 when  incubation  3:1 were  15  samples  time  of  used. The  minimize the potential  N.  8 low  inaccuracy  of  this assumption. Ethylene wounding, by  may  made  particularly  production  The  by  et a l . , 1977). The based  on  (Yoshinari using  gas  made  of  report  that  (Aulakh  the  in  of  N  by  anaerobic  evolution  2  its occlusion acetylene  principle  plant  tissue  as  soils  acetylene  acetylene  From  rate. A  inhibits  result  stoppers  (Sprent,  1979).  inhibits  evolution  measurements serious  problem  nitrification, which  al., 1982). In s y s t e m s  where  and by  Tests  for  of  denitrif ication  is  (Yoshinari  measuring denitrif ication is  the  of  of  necessary.  a product  inhibition method for  that  chromatography.  as  a  into ambient atmospheric nitrogen  and Knowles, 1976). The  denitrif ication  et  produced  in the absence of acetylene are  measurement  difficult  be  contact between terminating acids and rubber  microorganisms, ethylene  also  reduction  N 0 2  of  of  N 0  can then be N 0,  2  N  2  measured  estimates  2  to  can  be  is  the  with  this  method  yields  N 0  as a byproduct  nitrification  2  is significant, this  will  34 cause  underestimates  source  of  (1983) found not  2  in  Nitrification  be  rate-limiting  a study  of  northern  that N 0  production  2  of  production.  may  significantly  product  N 0  nitrate which  1982a). However,  was  of  in  in certain  hardwood  also  the  systems  forests,  such  that N  systems  and  was  2  Mel i I lo  not  that  major  (Knowles,  in the presence and absence of  different. This suggests  denitrif ication  is  et  al.  acetylene  a significant  the  inhibition  of  nitrification had no major impact on denitrif ication. Alternative  methods involve  Methods  using  N  have  been  marking  chemical  and  the  spectrometric  15  analysis  for  the use of  criticized cost  field  on  and  15  N - l a b e l l e d tracer  the  basis  relative  samples  with  of  compounds.  the  cost  insensitivity  low  activity  of  discriminate  (Blackmer use of  and  between . naturally  Bremner,  acetylene  offer  1977). For the  occuring  these  easiest  14  N  and  reasons, techniques  and simplest  means of  the mass  (Hardy  1973; Yoshinari et al., 1977). It has also been demonstrated that bacteria  of  et  al.,  denitrifying  isotopic  15  involving  the  measuring  N  ANF  and denitrification (Focht, 1978; Hardy et al., 1973).  5.1 FIELD The  3  PROCEDURES  experiments  designed (species  as  to  randomised  analyzed  strata were acetylene endogenous wood,  blocks.  foliage, bark Each  and  experiment  decaying involved  or decay classification) and 6 blocks (month). The  mineral soil experiment not  investigate  was  and  4  ethylene  10 samples  each  sampling  were  incubated  production. For forest were  period,  incubated  with  without  forest  floor  and  but  was  of  each  incubated  acetylene  were  treatments  12 samples  foliage and bark, 8 samples were  samples  3  designed as a 2X6 randomised block  statistically. At collected. For  wood  to  with  monitor  floor, mineral s o i l and decaying  acetylene  and  2 samples  without.  35 Sample  sizes  activity was  were  samples  turgor  could  be  as to  whether  in their For from  of  the  trees  might  collected  collected  X  3 2  nested  from  major  (top  have  species.  and forest  samples  were  Samples were were  equipped  atm  of  vacuum were  incubations.  left  to  to  of  was  questions  components  nitrogen  fixation. foliage  the  study  crowns  of  3 trees  designed  as  variation  done  in  site. of  a  3  between  an  incubation  fluorescent .and incandescent  lamps, in  the  dead  log  bark  of  mature, live  taken using trowel  sections  using  trees.  and  chainsaw  shovel.  and  axe.  from all size classes of w o o d y material.  septa  to  head space volume using  industrial  initial  grade  N 0 ambient  glass  mason jars.  acetylene  acetylene.  samples were  and  2  samples  1-L  The  amendments  of the jar was then amended to  equilibration, gas  wood  that  near  was  facilitate  and  on trees  lichen  block, with  experiment  from  rubber  determine  tissue  raised  for  area  with  for  wet  September/1984 using  logging  samples were  in the field under  Soil  in  into  1 hour  tubes  then  in  conditions.  floor  acetylene  approximately  potential  all placed immediately  and gas sampling. The 0.1  no  branches  developed  randomised  under  Samples were taken randomly  jars  samplings, as  scheme  experiment  taken from  taken  wrapped  and bottom  This  The  temperature  better  done  top  bottom)  samples were  soil  Wood  March  sampling  a fresh  the  then  a higher  was  at  an attempt to mimic summer  Mineral  and  taken from  have  species.  or  within  chamber, at room  Bark  and  ground. This  and therefore  trees  the  (species)  January  clipped  reason, an experiment  Foliage was  trees  were  from  older  crowns  mature  each  the  pressure. Samples were  reached  this  for  expected.  Foliage maintain  halved  C H 2  4  kept  for in  allowing  taken using  concentrations.  conditions  were  After  the boxes  5-mL  The  length of to  jars the  prevent  36 exposure  to  light  while  foliage  and bark  samples were  floor to mimic light conditions within the After  8  production.  hours,  vacuum  Preliminary  denitrif ication, therefore As rates of  the  goal  gaseous  of  tube  left  on the  forest  forest.  samples  experimentation  were  taken  produced  to  very  measure low  C H 3  4  rates  of  about  real  done under conditions  that  an incubation time of 24 hours was used. this  nitrogen  study  was  to  produce  flux, incubations were  information  mimicked natural conditions as closely as possible. Other than acetylene, no amendments  or  additions  were  made  to  the  samples.  aerobic, as anaerobic incubations might exaggerate Two results floor  additional  of  the  for  May  effect.  rate  further  experiment  60 ml of  limiting. The  and July To  were  was  using  done  a 5 mg L*  1  results were  a f-test  test  the  in  first  to  validity  which  of  material  nitrate  known  incubated. Four  samples  placed  in  and  in  immersed  water  to  was  stream  the  incubations  were  complete, sample  if  results,  mimic  wet  significant an  specifically  sediment their  environment. Other experimental procedures were as previously When  a  denitrify,  to  forest  determine  denitrif ication  of  low  denitrif ication rates  there  to  the  amending 6  solution  if  the  sediments, was jars  validate  compared to  stream  mason  to  involved  determine  were  fluxes.  conducted  denitrif ication a s s a y s . The  samples with  nitrate was  experiments  Incubations  were natural  mentioned.  weight,  oven-dry  weight, volume and % moisture content were determined.  5.2 LAB  ANALYSIS  Analysis  for  chromatograph 1.8  m  X  3  N 0 2  was  done  equipped with mm  glass  using  a  Hewlett-Packard  an N i " electron  column  packed  with  capture Porapak  5790A  detector Q-5  series  gas  and using a  (80/100  mesh).  37 Oven  temperature  rate was  1  60 °C, detector  25 ml m i n . Carrier  gas was  -1  Calibration was L* .  was  Response  by  external  was  temperature  in air of  2  to  be  250 °C  and  a 95% A r g o n , 5% Methane  standard using N 0  assumed  was  linear  based  on  flow  mixture.  1.5 and 52.5 mg  the  investigations  of  Kaspar and Tiedje (1982). Concentrations  of  C H 2  and  2  C H 2  were  4  measured  Hewlett-Packard 5830A series gas chromatograph using two stainless  steel columns packed with  ionization  detector. Nitrogen  columns  at  rates  injection  temperature  Calibration was  of  by  (N ) 2  30 and was  carrier  37 ml  105 °C  external  Porapak N (80/100 gas  flowed  m i n . Oven  and  1  detector  standard with  using  1.8 m X  a  3 mm  mesh) and a flame  through  the  temperature temperature  respective  was was  a linear response  50  °C,  130  °C.  assumed  over  the range of expected values.  5.3 C A L C U L A T I O N S Gas  chromatographic  This  value was  weight  results  multiplied by  and sample dry  in nmoles N g -  for  1  weight  denitrif ication  head space volume to produce  results  chromatographic m l " . This 1  value  divided by  sample dry weight  in nmoles  g  per  day  _ 1  value  per  was  then  acetylene  multiplied  to produce  8 hours. This  and  for  divided  value by  head  3  to _ 1  day . 1  1  molecular  2  were  space  to  expressed  volume  acetylene  multiplied by convert  L .  dissolved N 0 as  reduction  a measure of  was  producing a value in units of nmoles N g  by  mg  denitrif ication rate  1  Gas  in  and divided by  day- . This value was then corrected for Moraghan and Buresh (1977).  nmoles  expressed  a measure of  recommended by  in  were  3 to  and  reduction produce  nitrogen  a  fixation,  38 Mean rates of N g - ' dayof  kg  N  units  of  from  the  a . Multiplying  -1  weight.  The  number  X 365 days  number  of  active  of  molecular days  months  samples were  of  in kg N h a  weight  transforms per  year-long  active, activity  nmoles  to annual flux rates in units  activity  in the  of the year. Multiplying by  measure of flux  was  year  nmoles  was  calculated  sample. If  2 out  assumed to occur  total biomass h a  -1  to  of  on 2/6  then produced a  a .  -1  1  QUANTIFICATION biomass  regression of  by  - 1  the 6 monthly  Foliage  fixation and denitrif ication in units of  were calculated and then converted  1  ha  5.4 SITE  nitrogen  tree  was  equations  for  crowns, to  quantified  quantified  their  the  by  UBC  research  diameters  as during the course  measuring  of  (Table  tree  forest  diameters  relating  4). Bark  the experiment  and  foliage  surface  biomass  area  no nitrogen  using  was  not  fixation  was  measured in this stratum. Decayed w o o d  volume was quantified using Smalian's formula, V  where  = (A, + A ) X L / 2 2  measurements were made of: A j = t o p end diameter A = b u t t end diameter 2  L=section for  each  converted Density  piece to was  of  dry  decaying weight  calculated  wood  using as  M/V  length  present  densities where  on  the  study  calculated volume  site. Volume  from  was  selected  determined  displacement and mass was the o v e n - d r y (105 °C) weight Forest from  horizon  experimentally  floor depth  and mineral soil were and  calculated  area  and  then  densities. Bulk  quantified converting density  was  by to  was  samples. by  water  of the sample.  determining dry  caculated  weight for  volume using mineral  Table 4. Regression equations relating biomass of foliage (Y) to outside bark diameter at breast height (D), /nY(kg.) = a + b//?D (cm Source; M.C. Feller (unpublished data). Species  a  b  DF WRC WH  -1.216 -3.869 -4.130  1.286 2.100 2.128  SE(/n  units)  .216 .408 .435  r  2  n  .986 .930 .960  10 12 18  40 soil and relative density for determined uniform  by  water  throughout  forest floor  displacement  the  experiment.  while The  material. Forest mineral top  30  floor  volume  soil  volume  c m . of  the  was  active microbial activity, as  fixation  significantly  been  shown  to  decrease  with  depth  held  mineral  horizon was considered as the area of has  was  soil  nitrogen  (Baker  and  A t t i w i l l , 1984). Site  quantification  Table 2 (page 30).  results  and  sample  densities  were  presented  in  6. RESULTS AND DISCUSSION  6.1 NITROGEN FIXATION Nitrogen  fixation  Fixation  rates  acetylene  rates  are  total  indications  reduction  Endogenous  and  rates  ethylene  annual  of  and  potential  the  production  fluxes  are  nitrogenase  stoichiometric  was  not  presented  in  activity,  conversion  encountered  Table based  ratio  during  the  of  5. on 3:1.  course  of  the  this experiment.  6.1.1 FOREST FLOOR AND MINERAL SOIL The forest  most  floor,  input  due  agrees  which  to  with  important  accounted  biological other  substrate for  fixation  authors  for  nitrogen  fixation  was  80% of  a  measured  almost  of  0.8  (Silvester  kg  and  N  nitrogen fixation  Forest  floor  in the organic horizons  material will  have  higher  a - . This  - 1  finding  1  Bennett,. 1973; Granhall  Lindberg, 1980; Baker and A t t i w i 11, 1984) who of  ha  total  found the  of  and  highest  rates  coniferous forest  soils.  nutrient  status, higher  moisture  content and greater available carbon than mineral s o i l . Fixation rates in mineral soil were very nitrogen  in this substrate  reports  of  is 0.06 kg N h a  -1  low. The a - . This 1  total input  agrees with  of the  Roskoski (1980), Tjepkema (1979), and Granhall and Lindberg  (1980) that mineral soil  is a relatively  insignificant source of  nitrogen  fixation in northern temperate forests. An factor have  adequate  for a  • content)  nitrogen  higher than  C/N  supply fixation ratio  mineral  soil.  of  available  (Sprent, and  lower  carbon  1979). Forest 0  2  Heterotrophic  41  is  often floor  the  limiting  material  tension  (ie  higher  nitrogen  fixation  will  moisture  rates  have  Table  5,  Bimonthly  nitrogen Bimonthly  STRATUM  JAN  MAR  LFH  0.0  SOIL  0.0  n Decayed  W o o d  RDF W D F W R C n  Foliage  DF  W R C W H n Bark  DF  W R C W H n  fixation N  rates  Fixation  and  Rate  total (nmoles  annual N  g-'  fixation  for  Total  day ) 1  NOV  0.0  1.439(473)  0.55(.16)  0.27(.09)  0.23(.05)  0.61  0.0  0.02(.01)  0.0  0.01 (.003)  0.0  0.06  5  5  10  10  10  10  0.0  0.04(.05)  0.27(.08)  0.04(.03)  0.05(.02)  0.0  0.03  0.0  0.04(.03)  0.08(.03)  0.07(.03)  0.01  0.0  0.02  0.0  0.03(.03)  0.05(.02)  0.02(.01)  0.10(.04)  0.0  0.01  5  5  10  10  10  (.01)  errors  in  parentheses.  kg  N  Fixation  JUL  .10  SEP  Annual  MAY  ha-  1  a  0.0  0.18(.18)  0.47(,24)  0.67(.29)  0.0  0.0  0.03  0.0  0.34(.25)  0.13(.09)  0.24(,12)  0.0  0.0  0.01  0.0  0.0  0.25(.19)  0.29(.15)  0.0  0.0  0.00  8  8  8  5  5  10  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  5  5  10  8  8  8  TOTAL -standard  1984.  0.78  1  43 been  correlated  content and  with  and w i l l  decreasing  concentrations  correspondingly soil  moisture  of  organic  decrease  (Baker  and  matter  with  and  decreasing  Attiwill,  moisture soil  depth  1984; Granhall  and  Lindberg, 1980). Coniferous of  forest  soils  generally  molybdenum and phosphorus  have  low  both these nutrients  with decreasing soil pH (Jurgensen and Davey,  moisture  nitrogen  content  positively  rates  highest  occured  (Table  6).  decreases  rapidly  1970). in May  While  (Figure  nitrogen  5), when  fixation  correlated with temperature, high summer temperatures  correspond  to  periods  Moisture content apparently The  fixation  was  availability  may limit nitrogen fixation under these  conditions, as the availability of  Highest  pH. The  favourable  of  may  moisture  has been found to  optimum  absence  when  temperature  fixation  in  content  limit nitrogen  conditions  November  be explained by  is  higher  (Baker  when  often  relatively  low.  fixation rates  under  and  1984).  moisture  Attiwill,  conditions  mineral nitrogen  are  availability  November than May. Fall increases in nitrate in streamwater have observed  is  in  been  by Feller and Kimmins (1984).  6.1.2 DECAYING WOOD Nitrogen relatively  fixation  insignificant  by  free-living  (Table  3).  bacteria  Total  in decaying  annual  input  fixation in decaying w o o d was only 0.06 kg N h a Because a  skewed  Transformation visually  of  the  large  distribution failed to  in Figure  6. The  number and  correct  of  inactive  statistical this  greatest  - 1  was  nitrogen  a* . 1  analysis  occured  to  samples, the  problem. The  flux  due  wood  was  data are  in the  data had invalid. compared  month of  May  44  Legend  tZ3 FOREST FLOOR S 3 MINERAL SOIL  JAN  MAR  MAY JUL MONTH OF 1984  SEP  NOV  I  STANDARD ERROR  Figure 5. Nitrogen fixation rates in mineral soil and forest floor for 1984.  45  Table 6. Average moisture content (by percent) of sample material. Month of 1984 MAR MAY JUL  STRATA  JAN  LFH SOIL  208 22  208 20  259 23  Decayed W o o d RDF WDF WRCW  341 100 76  340 113 89  339 117 148  SEP  NOV  154 21  193 18  247 26  346 95 113  264 61 151  317 67 63  46 when, as with forest f l o o r , moisture content was high. Highest advanced  rates  stage  of  of  (1978)  have  decay  progresses.  fixation  decay.  reported  Jurgensen  that  Total  occurred  nitrogen  et  carbohydrate  nitrogen  tend  conditions  nitrogen  fixation  fixation  activity  in  more  the  (Jurgensen is probably  decayed  et  attributable  wood  (Table  decay  fungi  4)  et  al.  as  wood  soluble  sugar  have  been  total and soluble  would  The  to  Larsen  the  increase  which  1984).  in  rates  progresses, while  al.,  wood  a l . (1984) and  and  decay  increase,  Douglas-fir  fixation  shown to decrease as w o o d to  in  tend  increase  to in  inhibit nitrogen  increased moisture  and  consequently  content  reduced  0  2  levels. The  fact  material,  in  nitrogen  input  a-  1  have  forests  that  spite  of  a  high  exist. Nitrogen  been  reported  (Roskoski,  C/N  al., 1984).  anaerobic  incubations, which  ratio,  decaying  1980; Larsen  et  readily  fixation rates  for  Jurgensen  can  et  However, may  suggests from  wood  al.,  these  metabolize  that .sources  0.3 to in  Larsen  results  were  the  of  1.4 kg N h a  northern  1978;  exaggerate  woody  temperate  et  al., 1982;  achieved  nitrogen  1  using  fixation  by  anaerobic bacteria. Silvester et a l . (1982) suggested that microaerophilic bacteria may be the most in  decaying  wood.  In  important agent an  experiment  facilitating nitrogen comparing  incubated anaerobically and at different 0  2  was  5% 0 .  greatest  under  an  atmosphere  of  woody  fixation material  levels, nitrogen fixation rate 2  Still,  Silvester  et  al.  (1982) reported rates of nitrogen fixation in decaying D o u g l a s - f i r  wood  (4.8  rates  nmoles  reported  in  explained  by  N this  g-  1  day- , 1  study.  differences  1.4 kg This in  N  ha  - 1  discrepancy  incubation  yr ) 1  can,  far to  temperature.  greater some  than  extent,  Incubations  be  in the  47  1.5n  0  •o Ol  z « •5  E c  < z  o  0.5-  X  Legend  j ^ r j , 1%1 JAN  MAR  ri#U  MAY MAY JUL MONTH OF 1984  eZl REDROT Df O WHITEROT Df CEDAR  t^JS SEP  NOV STANDARD  Figure 6. Nitrogen fixation rates in decaying w o o d for 1984.  ERROR  48 Silvester  study  were  done  at  22°C, while  conditions  in  this  study  incubations  were  done  under  ambient  which  never  exceeded  were  lower  when  moisture conditions were  most  favourable  and 6). Furthermore, Silvester of  taking  ratio  samples of  and  prevent  experiment the  fixation  drying  reported  mason jars  large  al. (1982) emphasized the  volume  during  to  the  reduce the surface  course  here, condensation was  during  rates  et  by  incubations. This  increasing  17°C  of  the  oxygen  exposure  (Tables 3 importance  area/volume  incubation. In  observed  could have  and  on the inside decreased to  the of  nitrogen  nitrogen-fixing  bacteria. Nitrogen nitrogen  to  However,  fixation  woody  and  careful study  be  substrates,  nitrogen  microfloral  may  fixation  faunal  (Silvester  less  important  notably  may  crown  have  succession  in  a  than  other  wash  and  significant  decaying  inputs litter  rol.e  wood  fall.  in  and  of  the  warrants  et al., 1982).  6.1.3 FOLIAGE Nitrogen input  fixation  of  0.04 kg  N  available  literature  (page  exaggerated daytime, Stewart usually algae  due  fixation  to  ha  the  rates  (1974) has  associated with 1  a . These 1  17). The fact were  reported  higher than n i g h t - t i m e living  in  association  that  low  rates  rates reported although  assumed that  foliage  to  responsible  for  an  are  supported  by  the  here  may, in fact, be  incubations be  day-time  sphagnum  were  uniform  nitrogen  rates. Nitrogenase with  is  for  fixation  activity  moss,  was  respond dramatically to light (Granhall and Lindberg, 1980).  in  done 24  in  hours.  rates  are  blue-green  reported  to  49 Species and time of year were design.  The  preponderance  of  compared in a randomised block  inactive  samples  again  distribution to be skewed and statistical analysis was it appeared that in the  other  uniform  nitrogen  two  from  fixation  species  May  to  rate  (Table  was  5, Figure  July. The  drop  higher  the  invalid. However,  in D o u g l a s - f i r  7). Fixation  in foliar  caused  was  fixation  than  relatively  from  July  to  September may be related to moisture stress and decreases in nutrient uptake by  trees.  The algae  component  nitrogen this  presence  reached  from  their  epiphytes make  (Denison,  were  to whether in  may  fixation  study  of  the  with  level. This  from  samples  for  could  be  sampling scheme raised questions  as  better  position  (upper  differences  half,  at a fresh  lower  (Table 7). The  rate of  similiar  to  that  in  the  nitrogen  fixation  in  foliage  difference  found  in  this  foliage, not  supporting  between  to experimental  error.  an  inherent  difference  that  significant  species. fixation.  Western  fixation, suggesting  that these differences  of  only  claim  nitrogen  than  rate  the  experiment D o u g l a s - f i r was found to have the highest rate  other  highest  significant  previous  cause  the  was  for  in this foliage was  significant. The  experiment have  compared  crown  was  some  to  were  site. Species and  nitrogen fixation  younger was  logging  potential  hemlock  to  found  half)  higher  lichen components  collected  crowns  a  developed  that  fixation. A n experiment was carried out in which foliage was tree  have  trees  of  nitrogen  mature  therefore  younger  source  for  from  and  blue-green  a significant  1973; Millbank, 1978). Foliage  older trees might have  crowns  nitrogen-fixing  phyllosphere  collected primarily  ground  a  In  the of  may be attributable between  species  or  50  P JAN  MAR  I'm  l Legend EZJ DF o WRC • WH  i n  MAY JUL MONTH OF 1984  SEP  NOV  Figure 7. Nitrogen fixation rates in foliage for 1984.  I  STANDARD ERROR  51  Table  7. Nitrogen fixation rates(nmoles N g d a y ) and total annual flux (kg N h a a ) in foliage c o l l e c t e d from mature tree crowns (A) compared with foliage collected at ground level(B). _ 1  -1  Species  Fixation Rate  DF WRC WH n  0.138(.067) 0.353(.114) 1.018(.259) 12  TOTAL - s t a n d a r d errors  -1  -1  in parentheses.  Annual Flux A  in  Annual Flux in B  0.001 0.001 0.020  0.028 0.006 0.004  0.022  0.038  52 6.1.4 BARK Several (Todd has  et  writers  reported  al., 1978; Granhall  confirmed  trunks  have  in  the  and  Lindberg,  that  nitrogen-fixing  Pacific  Northwest.  fixation activity  nitrogen  lichens  However,  fixation  on  tree  boles  1980), and  Millbank  (1978)  occur  coniferous  on  in this  tree  study,  no  nitrogen  the  data  suggest  associated with bark was detected.  6.2 DENITRIFICATION Denitrif ication  results  are  summarized  in Table  8. While  that some denitrif ication occured, the total annual output of nitrogen due to denitrif ication was effectively redcedar w o o d  0.0 kg N ha-  and mineral soil were  (n = 10). S i m i l i a r l y , forest floor  1  a . Rates reported - 1  the result  of  only  rates were the result of  for  western  one active sample 3 active samples in  May and two active samples in July (n = 10, both months). Furthermore, it is unlikely  that  these  reported.  High  variability  in  (Robertson  and  measurements  standard  errors  denitrif ication Tiedje,  denitrif ication is a highly  accurate  support  rates  1984).  are  is  the  and  even Tiedje  the  positive  spatial variability  in  decimal  that  high  cultivated  (1984)  places spatial systems  suggested  that  in this study, often consisted  several active samples and a large proportion  diluted  4  variable process both among and within temperate  f o r e s t s . Their results, like the ones presented of  the  hypothesis  typical  Robertson  to  effects  of  active  of  samples. The  inactive samples which reasons  are not w e l l understood, although they  for  this  high  may be related to  the occurrence of anaerobic microsites and/or nitrification. The of  the  sediments  large  proportion  methods  used  were  assayed  of  in for  '0' results  this  study.  raised concern To  denitrif ication  test  these  about  the  validity  methods,  stream  potential. Denitrif ication  rate  in  Table  8.  Bimonthly  denitrif ication  rates  Bimonthly  W o o d  total  annual  denitrif ication  Rate(nmoles N  Denitrification  g-'  for  day )  errors  number  of  Annual  0.0002(.0001)  0.0  0.0  0.0003  0.0  0.0002(.0002)  0.0  0.0  0.0010  0.0  0.0  0.0  0.0  0.0000  M A Y  LFH  0.0  0.0  0.0005(.0003)  SOIL  0.0  0.0  RDF  0.0  0.0  JUL  (kg  N  h a '  W D F  0.0  0.0  0.0  0.0  0.0  0.0  0.0000  W R C W  0.0  0.0  0.0  0.0013(.0013)  0.0002(.0002)  0.0  0.0001  5  5  10  10  10  10  TOTAL  =  Total  1  SEP  MAR  n  standard  1984.  NOV  JAN  STRATUM  Decayed  and  in  parentheses.  samples  per  stratum.  0.0014  54 this material was 4.93 nmoles N g -  1  day  (standard error=.46) indicating the  -1  validity of the low rates determined for soil and decaying The  absence of denitrif ication in decaying w o o d  low  levels of  not  occur  of  mineral nitrogen  be  forest  for  (n=6)  both  were  denitrif ication Assuming of  rate  that  carbon  denitrif ication,  and  experiment  amended with  60 ml of  was  0.01 kg N h a  still  relatively occurs  a . The  -1  was  a 5-mg  for  at  of  a  N 0  loss in unfertilized temperate f o r e s t s " (Robertson little  information  general,  forest  soils  provide  a favourable  L"  with  about  high  environment  may  for  be  this  - 1  of  soluble  which  solution.  0.01) although N  g-  would  1  day- . 1  yield  tend to  a principle  denitrif ication  levels  <  should  in  nitrate  1  this experiment  suggestion  Very  production  out  0.012 nmoles  122 days  results  - 1  "nitrate  low  nitrate.  content  carried  the 2  coarse texture  moisture  increased denitrif ication rate (p  denitrif ication  that  supply  an  This treatment significantly  loss  in such environments. That denitrif ication did  available organic carbon and/or the lack of  floor, where  suitable  samples  may be explained by  in mineral soil may be explained by the relatively  the s o i l , the lack of  Using  wood.  support  determinant  and Tiedje,  1984).  in  exists.  forests  organic  denitrif ication. Several  a  of  In  carbon  should  recent  studies  (Melillo et al., 1983; Robertson and Tiedje, 1984) have suggested that nitrate production  may  Melillo  a l . (1983)  studied  hardwood  stands  et  sequence of rates of  nitrogen  1.4 kg N hathat  the  potential (1984)  be  1  a-  "true" was  studied  a dominant  loss were 1  using rate  highest  in  in  in New  denitrif ication  N 0  9 kg N h a  potential  over  -1  a-  1  using anaerobic  incubation. Melillo et  recently potential  loss  2  Hampshire. In a 50+  somewhere a  controlling  denitrif ication  aerobic lies  factor  between  logged in  a  number  year  old stand,  incubation and  two.  sites  suggested  Denitrif ication  Robertson of  forests.  successional  a l . (1983)  the  stand.  a  in  and in  Tiedje  Michigan  55 forests  and  nitrification  reported  2 to  12 kg N ha-  of  denitrif ication et  1  (<0.1  In  a - , although 1  kg N h a  sites  little  (Keeney,  flux  rates  a number  of  sites had very  low  rates  1  In  both  studies  nitrification  alter the physical  is  thought  practices  to  such  as  mineralization  return  model  in forests  nitrogen. A s  to  of  availability  will  take  be  Significant  rates  up  that  mineral  denitrif ication able  to  are  higher,  here found  for  been demonstrated  in  be  the  site  not  nitrogen  before  l o s s e s . If  nitrogen  nitrate  in the UBC  in  nitrification  soil  fully  nitrification  denitrifying  actively  Research Forest  taking  plants et  for  following  place,  trees thereby  available  may  nitrate.  clearcutting  have  (M. C. Feller , pers. comm.). 1  A s s i s t a n t Professor, Faculty of Forestry, University of British Columbia, Vancouver, B. C.  may  al., 1982).  occupied, forest takes  up  increase,  is occurring, the forest  bacteria  leachate  (Vitousek  nitrate reasons;  should and  that et al.  where  for' two  outcompeted  becomes  (Vitousek,  demonstrated  forests  a m m o n i u m - b a s e d nutrition as  slash  promote  saturation  clearcutting  proceeds, competition may  and  and may  have  in  are  bacteria  2.  unamended  clearcutting. Vitousek  mobility  following  in  clearcutting  and soil  trees  outcompete  increases  nitrate  greater  nitrifying  is  of  be  a predominantly  implication  preventing  may  succession  The  still  a  occur  and biological environment  increasing nitrate  suggested  populations  discussed  1984) denitrif ication was  denitrif ication may be more significant f o l l o w i n g  1.  for  had potential  1981). M e l i l l o et al. (1983) and Martin (unpublished)  mobility  potential  sites  and Tiedje,  1980). Forestry  denitrif ication by  (1982)  high  active  month- ).  -1  with  in spring.  forests,  burning w i l l  in  most  al., 1983; Robertson  to be highest  systems  rates  and respiration. The  of  (Melillo  highest  56 Martin resin  (unpublished) bags  evidence  in forest  that  has  an old growth - 1  N ha  1  the  to  this  differences  dynamics. The  old  growth  results  insignificant factor of  maturity.  increase  While  may  Figure  8  any  of  denitrified. Martin  a recent  clearcut  this  may  also  become  less  efficient  study  perturbation also  increase  the  be  due in  more  (10 kg than  can to  be  stand  taking  up  accessible  to  bacteria.  indicate that  such  (40 kg  forest  difference  become  and  much higher  they  to  the  denitrif ication is an  as  at its present  clearcutting,  potential  at future stages  for  in stand  that  state might  denitrif ication. development.  FLUX illustrates  ANF  the  total  rates  accounts  for  annual  were  gaseous  effectively  an input  of  zero  nitrogen (values  0.8 kg N h a  - 1  This  small  and  may  input  may  contribute  ecosystem.  Feller  and  precipitation  and streamwater  be to  Kimmins  significant a slow (1984)  runoff  accumulation  in the UBC  for  are  - 1  in balancing  reported  flux  the  study  magnified  a . This  with other published data for northern temperate forests  nitrogen,  absorption  supporting  old growth  some  denitrifying  in this  levels, might  site. Denitrif ication while  for  in the  mineral nitrogen  This potential may also be greater  6.3 T O T A L  being  in the functioning of this e c o s y s t e m  However,  nitrate  than  methodology,  presented  leachate  was  rates  anion  denitrif ication rates were  nitrifying bacteria and consequently The  solution  greater  stand  nitrogen, allowing  floor  by  Island, B.C. Rates in the clearcut  study.  in  fixation  in forest  on Vancouver  in  nitrate  denitrif ication  significantly  measured  available  floor  However, old growth  1  attributed  in forest  forest  -1  rates  not  determined  a ) were a ).  increased  f l o o r , but  nitrate  (unpublished)  N ha  found  10X)  is comparable  (Table 9). potential of  nitrogen  losses  nitrogen  in  fluxes  due  of this to  Research Forest. Their data  57  YZZZLZZZZ&ZL Legend IZ2 NITROGEN FIXATION •1 0.01  STRATA  Figure 8. Total annual nitrogen flux by strata.  DENITRIFICATION  58  Table Forest  9. A s y m b i o t i c  nitrogen  fixation rates in temperate  type:  forests.  Estimated kg N fixed ha a 1  Pine/spruce, 160 yrs old (Sweden) Pine, 120 yrs old (Sweden) Pine, 15-20 yrs old (Sweden) (Granhall and Lindberg, 1980)  3.8 u.o 0.3 0.3  Pine (South Carolina) (Jorgensen and W e l l s , 1971)  1.0  Deciduous (North Carolina) (Todd et al., 1978)  12.0  Deciduous (Massachusetts) (Tjepkema, 1979).  0.2  Deciduous, 4 yrs old (New Hampshire) Deciduous, 57 yrs old (New Hampshire) Deciduous, >200 yrs old (New Hampshire) (Roskoski, 1980)  2.0 0.4 1.6  Mixed conifer (British (this study)  0.8  Columbia)  59 suggest  a net  reported  here  year  input this  of  3 kg N ha  yields  slash  burning  1984, Table The  to  may  due  result  assumption  speculate  on  Similiar Flux  stages  of  nitrate  losses  of  4 kg N h a  combined  a net  flux  loss  the in  rates  of  be  gaseous  treatment nitrogen  increases  input  from  a - . Over  1  ANF  an 80  1  of  log  (Feller  ANF  export  and  and Kimmins,  nitrification. A s populations  and  Reiners by  clearcutting  nitrifying  and  be  clearcutting,  due to  mortality,  may  be  nitrate  may  as  hypothesized  that  productivity  removal  has  which  been  (Melillo  cited et  al.,  availability  is  and/or  outcompeted  again  both  later  Nitrate  grows old and becomes  forest  for  increased  , competition for nitrogen w i l l  bacteria  us  in the  denitrif ication  vegetation  allows  decrease  degrades  above. Evidence  clearcutting.  may  secondary  suggested  ecosystem  1980) and  following  thesis  during  (1975) have  net  described  (Roskoski,  mineral nitrogen. A s the forest senescence  following  succession proceeds of  flux  can  succession  in this  increase, as the forest  that  unpublished)  during  discussed  trends  controlled  similiar to  in  Martin,  be  uniform  nitrogen  greatest  and then  may  are  evidence  s u c c e s s i o n . Vitousek  increased f o l l o w i n g  to  the  successional  will  a pattern  1983;  of  changes  succession proceeds  shows  to  in  that  be justified. Some  processes.  and  input  the  8).  succession.  for  an annual  with  rotation, this amount will more than compensate for losses due to log  export. However, losses  not  a~\ Coupled  1  increase  for  available  less productive  become  more  due  readily  available for denitrif ication. Gorham et al. (1979) have suggested a similiar trend for A N F , related to  the - availability  nitrogen of  fixation  phosphorus  of  phosphorus,  (Granhall, in  forms  an  important  1981). There available  to  is  requirement  speculation plants  for  biological  that  the  availability  decreases  as  succession  60  Table  10. Nutrient losses, nutrient inputs in precipitation and nutrient reserves for logged (A), logged and slash burned (B) and undisturbed (C) watersheds in the UBC Research Forest. Values are in kg/ha for the two year period 1973-1975.  Streamwater export Log export Atmospheric export Total export Forest floor content Mineral soil content Total reserve Average annual precipitation input Source: Feller and Kimmins, 1984.  A  B  C  11 234  1  245  -  3 308 982 1293  1632 4566 6198  2180 4647 6827  1490 3924 5414  4  4  4 '  1  61 proceeds  (Gorham  et al., 1979). Similiar  will  greatest  following  be  clearcutting  and  accumulation of also  be  related  nitrogen  fixation  less  in  old  organic to  clearcutting.  growth  ecosystem  nitrogen, phosphorus  ANF  forests  matter on the  net  to  may  also  because  site  an  higher  increase  in  the  as  nutrients  may  important  available as the forest  for  becomes  efficient. Nitrogen  nitrogen  fixation after clearcutting may help to offset potentially  losses  due  to  denitrif ication  and  leaching. A s  the  site  reestablished, denitrif ication will become less significant and ANF a modest contribution to reestablishing the nitrogen  6.4 SOURCES During  the  OF ERROR course  of  error were  considered.  The  decision to  al.  (1982).  theoretical done  becomes may make  ' this  use  experiment  the  a  number  stoichiometric  Experimentally-determined  suggesting  of .potential  conversion  sources  factor  of  that  comparative  ratios  generally  C H - N 2  2  fixation  1 5  of  vary studies  in this  would  create  not  too  nitrogen  fixation  ratio of  2:1 would  al. (1982) found  study, it was great  in this result  the ratio  study  an  felt  that the  inaccuracy.  would  be  in a total flux to  use of Using  Silvester from  the  should  be  0.6 kg of  be 3.5:1 when  hours. Using this ratio, total flux in this study  N ha-  ratio 1  a  1.2 kg N haincubations  rates  the theoretical  a  1  of while  - 1  of  3:1, for  (Hardy et al., 1973; R o s k o s k i , 1981). Because of the low fixation  encountered  high  pool.  acetylene reduction to nitrogen fixation was based on the work et  after  (Roskoski, 1980). Increases  productivity  may become more readily  of  be  availability  ratio  4 : 1 , total using a  a - . Silvester  were  et  1  kept under 7  would be 0.7 kg N ha-  1  a . 1  62 The  incubation  technique  samples were cut from the  incubation  were  area/volume under  natural  conditions. these  underestimate  gaseous  or  rate to  anaerobic  These  consequently  overestimating  reduction  Similiarly, mineral  destructively.  and  a greater  Although  reduction  be higher  aerobic  Silvester  under  low  0  of  the  sample  material  material. more  Increased  susceptible  result  in  to  0  floor  than  2  were  et  (1982)  is  strongly  may,  drying  and  should  consider  turn,  acetylene  by  will  may  avoid  in  than under  affected  occur  to  found  area/volume  surface  might  done  incubation  into  samples  increased  aerobic al.  Wood  make them fit  concentrations  2  samples.  forest  incubations  surface to  and  exposure  processes,  fluxes.  soil  disturbances  conditions. Oxygen diffusion  content  disturbing  larger pieces and fragmented to  chambers.  sampled  necessitates  ambient moisture  make  cause  the  artifactual  effects. Future with  and  without  nitrification. 1978),  studies  If  denitrif ication  acetylene  to  determine  nitrification/ denitrif ication  inhibition  effectively  of  halt  of  nitrification  denitrif ication.  will In  the  uncouple  addition,  method  are  acetylene  indications  time. Extrapolating day  of  nitrogen  reduction nitrogen fixation  assay  measurement w i l l cause a decrease  and  high  spatial  Tiedje,  overlooked.  variability  1984)  suggest  reported that  and  the  coupled  (Knowles,  processes may  and  produce  at  acetylene  inhibition  a  point  measured over  specific 8 hours  in accuracy. Extrapolating  in this study this  inhibiting  these  per day to rates per month or year w i l l create an even The  of  nitrification  transformation rates  are  incubations  (Aulakh etal., 1982).  2  the  effect  processes  significant quantities of N 0 in some s y s t e m s Both  full  doing  source  of  in  to  a per  flux  rates  greater  inaccuracy.  and elsewhere  (Robertson'  error  should  not  be  63 The are  not  methods used in this study are inexpensive ideal.  Work  directed  to  improving  other techniques should be continued.  these  and easy to use, but  methods  or  developing  7. S U M M A R Y AND Evidence  has  accumulated  nitrogen  transformations  demand  for  wood  realization  that  inexhaustable  and  wood  fuel  of  cheap  kindled  studies  forest  floor  during  While  nitrogen  s m a l l , coupled significant nutrient  in  with  due  due to  asymbiotic  of  nitrogen  to  that  et  nitrogen  al.,  fertilizers  are  not  fixation  as  a  systems. nitrogen  fixation  biomass and the  1977; Todd  bulk  Increased the  biological  et  fixation  al.,  are  in  forests  slash burning  and  (Feller  1975).  generally  precipitation, they  accretion  log export and/or  biological  and  nitrogen  nitrogen  by  of  world  accumulated in forest  (Borman  to  inputs  contributing  losses  nitrogen  the  nitrogen  biological  suggested  succession  inputs  throughout  supplies in biological  have of  in  importance  (Todd et al., 1975).  chemical  interest  means of augmenting nitrogen  may be a major source  the  ecosystems  supplies  Ecosystem  indicating  in forest  fibre  have  CONCLUSIONS  may  be  offsetting  and Kimmins,  1984). Interest fertilizer  nitrogen  atmosphere the  exists  where  depletion  generally and  little  loss  (Rolston,  it  involved  of  thought  in denitrif ication because  is  ozone to  However,  (Feller,  pers. comm.)  (Knowles,  and  it  1982a).  because  normally  clearcutting  and  occurs  may  not  increase  to  2  which in  occur  undisturbed  significantly  denitrif ication  reactions  N 0  Denitrif ication  it does in  mechanism  contributes  in stratospheric  be minimal  nitrification  1980).  1981)  it is a major  result  forests  without  systems nitrate  (Martin, unpublished;  of the in is  nitrate (Keeney,  availability  Melillo  et al.,  1983). The fluxes  due  coniferous  objectives to  of  asymbiotic  forest.  Eleven  this  study  nitrogen strata  were  to  fixation  and  were  64  sampled  quantify  gaseous  denitrif ication bimonthly  for  in the  nitrogen a  mature year  of  65 1984. Gaseous Forest N  ha  floor  nitrogen  s m a l l . Fixation  rates were  year  log  slash  export, also  has  rate  effects  nitrogen  input  burning  and  of  of  research site  on  treatments  during the course  improving  techniques  provides  an  of  and  such  as  in  of  for  nitrogen  in terrestrial  environments  atmospheric  nitrogen nitrates  foliage  was  relatively  fixation  over  forest  due  to  of  an  be  in f o o d  course  will  result.  management as  a  (Granhall  ANF  While  losses due  treatments.  steady  to  This  accumulation  of  and Lindberg, 1980). should  and  focus  burning,  on  the  scarification  denitrif ication  may  also  s u c c e s s i o n . Research must also focus both  processes.  method  The  for  use  of  measuring  on  acetylene ANF  and  inaccuracies exists. has  (Delwiche,  will  nitrogen  denitrif ication  easy  fixation  the  to balancing nitrogen  of  measuring and  of  clearcutting, slash  rates  forest  inexpensive  Industrial  and  zero.  input of 0.8 kg  w o o d , probably  occuring  ANF  denitrif ication but the potential for  increase of  effectively  decayed  64 kg  other  advantage  fertilization. ' Changes  occur  of  it may contribute  the  wood  in more  released, easily available nitrogen Future  and  denitrif ication were  capacity.  rotation, a net is small  slowly  to  decaying  greater  an equal  this amount  input  in  moisture holding  Assuming eighty  fixation  - 1  its greater  due  material was responsible for 80% of a nitrogen  a . Nitrogen  - 1  losses  increased  the  1981). While  depleted,  and water  there  fixed  there is  pool  is no  concern  and increased N 0 2  of  nitrogen  concern  that  regarding  the  concentrations  in  the atmosphere. Nitrogen and are subject fixation offers of  fertilizers  are becoming  to potentially an interesting  increasingly  expensive  (Beuter,  high denitrif ication l o s s e s . Biological alternative  maintaining or enhancing forest  to the forest  productivity.  1979)  nitrogen  manager, as a means  66 Our asymbiotic these  nitrogen  processes  relationship further  knowledge  to  attention.  of  fixation in  each  biological and  forests, other  and  nitrogen  denitrif ication their other  transformations is  response nitrogen  such  incomplete. The to  treatment  transformations  role  and  as of their  warrants  LITERATURE CITED  Alexander,  M. 1977. Introduction Inc. pp 2 9 3 - 3 0 8 .  Allison,  E. 1965. 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