THE INFLUENCES OF TEMPERATURE AND SOIL-WATER ON GROWTH, PHOTOSYNTHESIS, AND NITROGEN-FIXATION OF RED ALDER (ALNUS-RUBRA) SEEDLINGS

A 3 x 2 factorial experiment was conducted to investigate the interaction of temperature and soil water status on the growth, photosynthetic, transpiration, and nitrogen fixation rates of 2-month-old red alder (Alnus rubra Bong.) seedlings. Three day:night temperature treatments, 15:10-degrees-C, 20:10-degrees-C, and 25:10-degrees-C were used. Two soil-water treatments kept pots between 85 and 100% of field capacity (wet) and 70-85% of field capacity (dry). Treatment effects on growth, net photosynthetic, transpiration and nitrogen fixation rates, plant water potential, and foliar nutrient concentration were measured over a 9-week period. The greatest seedling growth occurred at 25-degrees-C day temperatures, while 20 and 25-degrees-C days produced the greatest nodule growth. The allocation of biomass to roots increased with decreasing temperature. The highest rates of net photosynthesis occurred at 15 and 20-degrees-C whereas transpiration was greatest at 25-degrees-C. Plant water stress was greatest at 25-degrees-C. The difference in plant water potential between the wet and dry treatments was only 0.04 MPa, which was not great enough to produce significant effects on growth or photosynthesis. Nitrogen fixation rates were highest in the wet treatment seedlings at 20 and 25-degrees-C.