Precipitation is predicted to fluctuate more greatly in most terrestrial ecosystems in the future, thus jeopardizing many structures and functions of ecosystems. High biodiversity in general insures stability of ecosystem productivity, by the mechanism of interspecific compensatory effects (e.g., different species respond differently to changing precipitation). Underlying the mechanism of the compensatory effect is the variation of plant functional traits that determines the magnitude of the effect in response to changing environment (e.g., precipitation). The challenging questions, however, are: (1) what traits matter to compensatory effect and (2) how much of the variation in traits is plastic and how much of that is species specific? In this study, we are interested in traits that affect species’ response to changing precipitation. We conducted a 5-year field precipitation manipulation experiment in a semiarid steppe in northern China with 5-level of precipitation, including 30% and 60% precipitation increase in growing season, control level (i.e., natural ambient precipitation), 30% and 60% precipitation reduction in growing season. We collected 12 traits of 10 most abundant species and calculated their plasticity.
Results showed that manipulated precipitation significantly affected aboveground net primary productivity and leaf area index, but did not induce changes in community species richness and Shannon diversity. Species showed varied response intensity and direction to the changed precipitations that maintained the relative stability of the community. Species with shallower roots and more roots in surface soil tend to respond to precipitation more strongly, suggesting that traits related to water absorption (root traits) are the most important in determining species' response to precipitation. Higher leaf:stem ratio was also an important factor triggering species’ response to precipitation. We also found that with the increase of plasticity of individual density and leaf: stem ratio and decrease of plasticity of water use efficiency, plants respond to precipitation more greatly. This suggests that greater plasticity of plant growth-related-traits tends to enhance the effect of precipitation on plant productivity. Finally, sensitivity analysis showed plasticity plays a greater role in plant’s response to changing precipitation than traits. This study reveals that traits and plasticity both are important to the operation of interspecific compensatory effect in response to precipitation change. This finding highlights the role of plasticity in maintaining ecosystem functioning that is often overlooked in the literature.