AN ANALYSIS OF DRY MATTER PRODUCTION OF DOUGLAS-FIR SEEDLINGS IN RELATION TO TEMPERATURE AND LIGHT INTENSITY

Abstract

Seedlings of Douglas-fir (Pseudotsuga men-ziesii) were grown in growth chambers under all combinations of 3 temperatures (13, 18, and 24 oC) and 3 light intensities (450, 1000, and 1800 ft-c). Dry matter production of leaves, stem, and roots was determined at 65 and 100 days after germination. The leaf area produced per unit of leaf dry weight and the dry matter distribution to the plant organs was measured. Net assimilation rates between the ages of 65 and 100 days were calculated. Rates of photosynthesis per unit of leaf were determined at different light intensities and temperatures, and rates of respiration of plant top and of roots were found for different temperatures. Increasing light intensity affected dry matter production in 2 opposing ways: it increased the rate of photosynthesis per unit leaf area; and it decreased the leaf area added per unit of dry matter produced. A pronounced increase in growth with increase in temperature from 13 to 18[degree]C was a result of a temperature influence on production of leaf area rather than the effect of photosynthesis per unit of leaf. Net assimilation rates decreased with increase in temperature at all light intensities.