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Low soil temperature and efficacy of ectomycorrhizal fungi

University of British Columbia

The influence of root-zone temperature on the efficacy of various ectomycorrhizal fungi, i.e., their ability: (1) to colonize roots in a nursery environment, (2) to persist and colonize new roots in the field and (3) to improve the growth, nutrition, and physiology of white spruce (Picea glauca (Moench) Voss) seedlings, was examined in controlled environment experiments using water baths to regulate root-zone temperature. Eight-week-old non-mycorrhizal seedlings were inoculated with 13 different inocula (1 forest floor inoculum, 12 specific fungi), then transplanted into 6, 16, or 26°C peat:vermiculite mixes for 8 weeks. Maximum root colonization occurred at 16°C for most inocula. The 6°C mix strongly reduced mycorrhiza formation with only 8 of the 13 inocula forming any mycorrhizae during the 8-week test period. Primary infection from ectomycorrhizal propagules (spores and hyphal fragments) was reduced more than was secondary infection from established mycorrhizae; once established, all inocula colonized new roots in 6°C forest soil. Fall-lifted cold-stored seedlings infected with 8 inocula (forest floor, 7 specific fungi) were planted into 6 and 12°C forest soil mixtures with or without indigenous ectomycorrhiza inoculum. Survival and colonization of new roots by inoculant fungi was good (> 50%) for the 12-week test duration despite the significant potential for infection by indigenous inoculum. High persistence appeared to be due to successful (>75%) root colonization by the inoculant fungi in the nursery production phase, to the relative weakness of ectomycorrhizal propagules (spores and hyphal fragments) compared with live ectomycorrhizal attachments, and to the favorable pattern of lateral root egress from the container plug after planting. Colonization of new roots by established mycorrhizae showed an effect of soil temperature in the presence, but not the absence, of indigenous inoculum. Percent new root colonization by inoculant fungi was lower in the 12°C forest soil. Rapid extension of lateral roots in the 12°C soil increased the likelihood that short roots initiated near the tips of elongating roots would be infected by indigenous fungi. There was no evidence of active or passive interactive replacement between inoculant and indigenous fungi. However, Hebeloma crustuliniforme appeared to inhibit mycorrhizal formation by indigenous fungi; roots not infected by this fungus remained non-mycorrhizal. Application of slow-release fertilizer reduced new root colonization by E-strain but had no effect on colonization by H. crustuliniforme or indigenous forest floor fungi. Non-inoculated seedlings (controls) and seedlings inoculated with 5 different inocula (forest floor, 4 specific fungi) were planted in 6 and 12°C forest soil for 3 weeks. Inoculation influenced the rate at which seedlings acclimated to the 6°C soil with respect to resistance to water flow and net photosynthetic rate, but had no effect on pre-dawn stomatal conductance. Differences among inoculation treatments were related to the size and nutritional status of seedlings at the time of transplanting. Seedlings infected with Laccaria bicolor or E-strain exhibited the least decrease in resistance to water flow due to the relatively small size (dry weight, short root number) of their root systems at the time of transplanting. Net photosynthetic rate and new foliage production correlated positively with shoot N and P (% dry weight) and the proportion of total seedling N and P contained in shoot tissues at the time of planting. Non-inoculated seedlings (controls) and seedlings inoculated with forest floor or 5 specific fungi were planted in 6 and 12°C forest soil for 12 weeks. The presence of "any" mycorrhiza at the time of transplanting did not improve seedling growth under the experimental conditions (i.e., cool, acidic soils with an indigenous ectomycorrhizal fungal population). On average, mycorrhizal infection increased N and P uptake at 12°C but not at 6°C. Growth response to specific fungi was very variable with some fungi depressing seedlings growth (e.g., E-strain and H. crustuliniforme) and others strongly promoting it (forest floor inoculum, L. bicolour, Thelephora terrestris). Seedling response to the various inocula was not related to the degree of mycorrhizal infection at the time of planting nor to the source of inocula; but was associated with differences in the content and distribution of nutrients at the time of transplanting and differences in total nutrient uptake, root efficiency, nutrient-use efficiency and net photosynthetic rate after transplanting. Root efficiency was not proportional to the number of short roots per unit root or to the amount of external mycelium attached to the various mycorrhizae. Implications for applied forestry and research are discussed in the final chapter.

Text

2011-01-28

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http://hdl.handle.net/2429/30930

Forestry

University of British Columbia

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