Drought effects on net CO2 exchange in the southeastern US

The mechanisms controlling daytime net ecosystem exchange are examined using the eddy-covariance method over a rainfed peanut field in the southeastern US. This paper reports the presence of hysteresis in net ecosystem exchange observed in both non-stress and water stress conditions as a function of photosynthetically active radiation, but shows that the magnitude of the hysteresis was much larger during the water-stress days than the non-water stress days. This resultant hysteretic loop is caused by a combination of decreased stomatal conductance during water stress and higher soil respiration in response to higher temperatures. The systematic presence of hysteresis in the response of net ecosystem exchange to photosynthetically active radiation suggests that the gap-filling technique based on a non-linear regression ought to take into account the presence of extreme environmental conditions such as drought.