Long-term dynamics of water and carbon in semi-arid ecosystems: a gradientanalysis in the Patagonian steppe

We used a soil water simulation model and remotely sensed data to study the long-term dynamics of transpiration, evaporation, drainage and net primary production across a precipitation gradient in Northwestern Patagonia (Arge ntina). The proportion of precipitation transpired, the precipitation use e fficiency and the transpiration use efficiency were constant across the gra dient that covered a range of 150 to 600 mm. The proportion of water evapor ated was higher than the proportion drained at the driest extreme of the gr adient. The opposite relationship was observed at the wet extreme. Two important characteristics of arid-semiarid systems dominated by winter precipitation emerged from our analyses: the importance of drainage losses and the asynchrony between evaporation and transpiration fluxes. These char acteristics of the water dynamics influence the relative abundance of plant functional types and are crucial to generate heterogeneity at the landscap e level. The coefficient of variation (CV) of transpiration, evaporation an d ANPP was, in general, lower than the CV of annual precipitation. This pat tern suggests a buffering capacity of the ecosystem. The ecosystem would be able to damp at the functional level inter-annual changes in the availabil ity of resources.