UBC Theses and Dissertations

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UBC Theses and Dissertations

Nitrogen and conifer studies Mellor, Gary Edward

Abstract

Part 1 The vascular bundle of leaves with the C₄-pathway of photosynthesis is usually surrounded by two concentric chlorophyllous cell layers: an outer mesophyll layer and an inner bundle sheath layer. The localization of the nitrate-assimilating enzymes, nitrate reductase, nitrite reductase, and glutamate dehydrogenase in Zea mays, Gomphrena globosa, and Sorghum sudanense was studied by differential grinding. Nitrate reduction to nitrite appears to occur primarily in mesophyll cells. The nitrate content of the mesophyll cells was much higher than the nitrate content of the bundle sheath cells. The distribution of nitrite reductase seemed to be related to the presence of chloroplasts with grana. Ammonia incorporation into organic compounds by glutamate dehydrogenase was localized in the bundle sheath cells. Part 2 Four conifer species, Douglas-fir (Pseudotsuga menziesii var. menziesii) (Mirb.) Franco, Western redcedar, (Thuja plicata) Donn, Western hemlock (Tsuga heterophylla) (Raf.) Sarg, and Lodgepole pine (Pinus contorta var. contorta) Dougl., were grown on three different sources of nitrogen (nitrate, ammonia, and a combination of nitrate and ammonia 7:1). A linear relationship was found between leaf area and leaf dry weight for three species (Douglas-fir, Lodgepole pine and Western hemlock). Different nitrogen treatments had no effect on this relationship. Part 2-A In this part the tree seedlings were grown for 18 weeks. For Douglas-fir, Western redcedar and Western hemlock, survival and growth on the nitrate solution was similar to survival and growth on the combination solution. Ammonia was an unfavorable source of nitrogen for survival and growth of Douglas-fir and Western redcedar. For Western hemlock, ammonia was only detrimental to survival. Hemlock seedlings which survived ammonia treatment grew as well as trees growing on the other two sources of nitrogen. Lodge-pole pine survived equally well under all treatments and was the only species that grew best on ammonia. Part 2-B At 18 weeks the seedlings were transferred from sand culture to liquid nutrient solution. The solution was changed every two days for a period of six days. The pH of the solutions was measured when the solutions were changed. At the end of the six days, the starch content of the plants was measured. The results indicate that these forest species differ in their tolerance to ammonia. Western hemlock and Lodgepole pine seem to be able to tolerate higher levels of ammonia than Douglas-fir and Western redcedar. Part 2-C In this part the seedlings were grown for a period of approximately one year. The trends shown in the 18 week experiment were confirmed in the longer experiment and some additional treatment effects appeared. Part 2-D In this part the seedlings were grown for a period of approximately one year. Within each species, an attempt was made to correlate differences in growth among nitrogen treatments with differences in gas exchange. It was found from calculations of stomatal resistance (r[sub s]) that the entry of CO₂ was not limiting dry matter production. It is postulated that mesophyll resistance (r[sub m]) may be a factor involved in controlling growth in these trees. Part 3 Two-year old (2-0) Douglas-fir (Pseudotsuga menziesii) seedlings were lifted in the spring and mud-packed. These seedlings were tested for the effects of various storage conditions. Mud-packed seedlings, stored in the field for 19 days and subsequently planted, had higher survival and root growth than those having other storage conditions. The other storage conditions included higher and lower temperature than in the field and light versus dark. Treatment of the mud-packs with fertilizer and vermiculite had no effect on any of the parameters measured.

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