Community And Species-Level Responses To Changed Precipitation Regimes In Inner Mongolia Typical Steppe

Global atmospheric circulations are greatly affected by anthropogenic activities. Several atmospheric circulation models predict that the frequency of extreme precipitation events, such as extreme drought and extreme rainfall and the variation of total precipitation, will increase in the near future. Water is the most limiting resource for growth and development of plants in arid and semi-arid ecosystems. Furthermore, grassland ecosystems have been proven to be very sensitive to changing precipitation regimes. However, our understanding on how changed precipitation affects grassland ecosystems is inadequate. Exploring community-and species-level responses to changed precipitation regimes is critical for better understand these changes.Our experiment was conducted in Inner Mongolia Grassland Ecosystems Research Station, Chinese Academy of Science. With six rainout shelters controlling growing season precipitation amount and patterns, we examined the response at the community and species levels to changed precipitation regimes. The key findings are as follows:(1) With the increased amount of growing season precipitation, mean soil water content increased significantly and so did the total variation while the variation of soil water content in up-layer (0-20cm) decreased. Changes in precipitation patterns did not significantly alter the mean soil water content but increased its total variation.(2)Aboveground biomass also increased significant with the increased amount of growing season precipitation. We found a liner relationship between aboveground biomass and mean soil water content for precipitation amount treatments. Among precipitation pattern treatments, the lowest aboveground biomass was observed in the 1:1 ratio treatment (the amount for early-versus middle-growing season was equal). In addition, no significant effect of changed growing season precipitation amount and patterns on belowground biomass was found.(3)Community coverage increased significantly with increased amount of growing season precipitation, especially the increase in mid-stage of growing season. By contrast, community diversity was not significantly affected by seasonal precipitation amount and patterns. For the responses of plant functional groups, a significant increase with increasing precipitation amount was found in perennial bunchgrasses and in perennial rhizomes, however, no significant change was found in perennial forbs and in annual/biennials. No significant effect of precipitation on the biomass was found for all four functional groups.(4) At the species level, we examined the responses of four major species: Achnatherum sibiricun, Stipa grandis, Carex korshinskyi and Leymus chinensis. With the increase of precipitation amount, the height, coverage and abundance followed a unimodal pattern in A. sibiricun and S. grandis, a linear increases in L.chinensis, and a saturating pattern in C. korshinskyi. The biomass of A. sibiricun, S. grandis and L. chinensis increased linearly with the increase in precipitation amount while that of C. korshinskyi was not significantly affected. The biomass of L. chinensis was positively and linearly correlated with mean soil water content. There was no significant effect of precipitation pattern on height, coverage and abundance of four species. No significant difference among precipitation pattern treatments was found in biomass of A. sibiricun and L. chinensis. For the R1:8 treatment (the amount for early-to middle-growing season was 1:8), the biomass in S. grandis and in C. korshinskyi was significant higher than others. No significant correlation was found between biomass production and soil water content for four species across all precipitation pattern treatments.