Soil moisture effects on transpiration and net carbon dioxide exchange of sorghum

Abstract

This field study was conducted to determine the effect of soil moisture on net carbon dioxide exchange (NCE) and transpiration rates of sorghum ( Sorghum bicolor (L.) Moench) grown under well-watered and water-stressed conditions. Components of the energy balance, soil moisture, leaf and air temperatures, stomatal resistance, and leaf-water potential were measured. A field growth-chamber system was used to determine NCE and transpiration rates. Analysis of the data suggested that transpiration and NCE rates were reduced when available soil moisture was ⩽35% of the maximum. Above that moisture level, transpiration was primarily energy-dependent and the rate was enhanced by air temperatures higher than 33°C. Photosynthetic rates declined when leaf temperatures exceeded 33°C. At and below the critical soil-moisture level, leaf-water potential decreased and the resistance to vapor transport increased; that reduced transpiration and NCE rates.