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The effect of soil temperature on nitrogen form preference in three British Columbia coastal conifers

Gaudet, Tabitha. 2012. University of Victoria, B.Sc. Honours


This study evaluated the influence of soil temperature on nitrogen form preference in three British Columbia coastal conifers. Douglas-fir, yellow cedar, and western hemlock were sown in pairs into 8 cm diameter pots in a 1:1 sand: peat moss mixture and grown at ambient air temperature in a greenhouse. Seedlings were grown at soil temperatures of 10, 16 or 20°C and given one of three nitrogen treatments 1) 90:10 nitrate: ammonium, 2) 90:10 ammonium: nitrate or 3) 50:50 arginine: alanine. After 6 months, seedlings were harvested and seedling morphological parameters and nitrogen concentration were measured. Total biomass significantly increased with soil temperature for Douglas-fir and yellow cedar. Growth of western hemlock was not significantly affected by soil temperature. Since most other plant species are expected to increase their growth and N uptake with warming soil temperatures, western hemlock may be relatively less fit in a future with warmer soils. Yellow cedar was the only species to show a significant interaction between the nitrogen form treatment and soil temperature. At 10°C, yellow cedar grew better with ammonium, however, this preference switched to nitrate as soil temperature increased to 20°C. This soil temperature interaction with N form presence may indicate that yellow cedar will perform relatively better on disturbed sites and at lower elevations where relative NO3 -availability is high as global temperatures rise.