Shrub encroachment has become an important ecological problem in arid and semi-arid grasslands in China. Because that water availability is a limiting factor for plant growth in these grasslands, precipitation changes are assumed to have critical impacts on shrub encroachment process under future climate change. However, there is little evidence from the vast grasslands to assess how changes in precipitation would affect the process. In this study, we conducted a 3-year precipitation manipulation experiment (-30%, ambient, +30%, +50%) to evaluate the effects of precipitation change on the growth of shrub and herbaceous species in a shrub encroached grassland in Inner Mongolia.
Results/Conclusions
At the community level, the shrub species showed almost no changes in the mean height and aboveground biomass (AGB) under different experimental precipitation, but the annual AGB increment (ΔAGB) decreased slightly with increasing precipitation. By contrast, herbaceous species showed a significant increase in the mean height and AGB at higher experimental precipitation, and the ΔAGB also increased significantly with increasing precipitation. We ascribed these differential responses of shrub and herbaceous species to precipitation change to the different eco-physiological responses among them. The maximum photosynthetic rate (Amax) and photosynthetic nitrogen use efficiency (NUE) in the dominant herbaceous species Leymus chinensis were more sensitive to precipitation change than those in the dominant shrub Caragana microphylla. At low soil moisture, the Amax and NUE of the C. microphylla were higher than those of the L. chinensis, and this difference decreased with increasing soil moisture. Moreover, the instantaneous and long-term water use efficiency of L. chinensis was higher than C. microphylla under different soil moisture contents. The above results suggest that the increase of precipitation are expected to increase the herbaceous growth but decrease shrub growth, which may slow down shrub expansion in the arid and semi-arid grasslands.