Slope aspect has effects on productivity and species composition of hilly grassland in the Xilin River Basin, Inner Mongolia, China

In order to investigate the productivity of hilly grassland of the Xilin River Basin as affected by slope aspect (North versus South), aboveground green biomass (AGB) and species composition were studied at four hill sites in 2005. Additionally, a detailed investigation combining vegetation parameters, physical and chemical soil characteristics was carried out at different slope positions (base, middle, and top) of north and south slope aspect on one of the hills in 2004 and 2005. Northern slopes exhibited a higher productivity and species diversity compared to southern slopes. Plant available soil K, P and N were not limiting the productivity at south- relative to north-oriented slopes, whereas soil available water was the primarily limiting factor for plant productivity, which was supported by results of leaf carbon isotope discrimination of main species. A negative correlation between productivity and relative abundance of C4 plants indicates that the relative biomass of C4 plants can be used as a water-stress indicator.