Variations in water and CO2 fluxes over a saline desert in western China

We studied the variations in water and carbon dioxide fluxes of a saline desert in western China using the eddy covariance technique. In addition, bare-soil evaporation was measured using the micro-lysimeter method. The following three inquiries were made: (1) the magnitude of evapotranspiration (ET) and net ecosystem carbon exchange (NEE) and how these components vary seasonally; (2) how NEE and ET vary following rain pulses of different magnitudes; and (3) how ET divides into evaporation and transpiration and its relationship to carbon dioxide exchange. The saline desert acted as a net C sink of - 49 g C m-2 year-1, with a gross ecosystem productivity (GEP) of 345 g C m-2 year-1 and an ecosystem respiration (Reco) of 296 g C m-2 year-1. Rainfall pulses exerted strong control over ecosystem-scale water and CO2 fluxes. There was a 1 to 2 days lag in maximal ET despite the magnitude of rainfall pulses, while NEE took 45 days to reach its peak if the rainfall was large enough to increase the photosynthetic activity of vascular plants. Overall, the ratio of total transpiration to ET was 38%, but it was about 92% during the months when the vascular plants were active. The NEE was increasingly more negative as the growing season progressed, indicating a greater net uptake of CO2 and a greater water use efficiency. Copyright (c) 2011 John Wiley & Sons, Ltd.