Effects of ozone and water stress on net photosynthetic rate of field-grown soybean leaves
Detailed physiological measurements were taken in controlled field experiments to better elucidate how environmental stresses interact to affect a soybean plant's physiology and growth. Nondestructive techniques were used to measure weekly and diurnal effects of ozone and water stress on net photosynthesis, stomatal resistance, and water status of field-grown soybean leaves. Open-top field chambers were used to expose soybeans to seasonal 12-h/day mean concentrations of 0.018 (CF), 0.059 (1.3NF) and 0.085 (1.9NF) ppm ozone. Soil water levels were well watered (WW) and water stressed (WS). Net carbon exchange-rate measurements (CER) were taken between 1000 and 1230h EST on center trifoliates with uniform exposure to sunlight. Average CER rates expressed as percent of CF over the growing season were 75% and 55% for WW 1.3NF, and 1.9NF and 90% and 61% for WS 1.3NF and 1.9NF, respectively. Measured mean seasonal photosynthesis rates of the WS CF treatments were 68% of those for the WW CF treatments.