Seasonal Carbon and Water Balances of Soybeans Grown Under Stress Treatments in Sunlit Chambers

SOME agricultural research issues require that engineers provide continuous monitoring and treatment control of plant environments over seasonal time frames under field-like conditions. In such a system, complete mass balances of C02 and H20 were maintained on six soybean canopies grown in sunlight at two C02 treatment levels, 330 and 660 pmiol mol '.In each set of C02 treatments, the three canopies were differentially watered to create one non-stressed canopy and two water stressed canopies. Seasonal balances were based on daily integrated values of transpiration, daytime C02 exchange and nighttime C02 exchange. Canopies were completely harvested for total biomass and yield determinations at the end of the growing season. Final biomass and yield were increased by C02 enrichment and decreased by water stress. The water stressed high C02 treatments yielded more than the continuously well watered low C02 treatment. On average, the high C02 canopies transpired about 10% less water over the season than did the low C02 canopies. Cumulative seasonal net CO, exchange rate correlated linearly and positively with seasonal biomass accumulation (R = 0.99) and seed yield (R = 0.95). A simple linear correlation between seasonal transpiration and yield (or biomass accumulation) did not hold across C02 treatments (R = 0.16). However, when C02 treatments were separated, yield showed a strong correlation with seasonal transpiration for low C02 (R 0.95) and high C02 (R = 0.99) conditions. These whole canopy results are based on the continuous competent operation of the environmental chamber systems throughout the 108 day season and confirm the unique utility of this research tool.