Legacy effects of nitrogen deposition and increased precipitation on plant productivity in a semi-arid grassland

Nitrogen (N) deposition and increased precipitation were widely reported to promote plant productivity in terrestrial ecosystems. However, few studies have explored the effects of historical resource supplements on plant communities (legacy effects). Based on a field experiment, we examined the legacy effects of N deposition and increased precipitation on plant productivity in a semi-arid steppe after the cessation of 13-year N and water addition. We found historical N and water addition generally had positive effects on plant productivity even after the treatments were ceased. However, such legacy effects showed strong inter-annual variation, and the positive effects of historical N and water addition on productivity were stronger in a wet year (i.e., 2019) than in an extreme drought year (i.e., 2018). Although N availability decreased rapidly, the positive effect of historical N input persisted after 2 years of cessation largely due to the maintenance of the enhanced community plant stature (CWMstature) through the increased stature of all functional groups. Moreover, the dominance of tall grasses persisted in water added plots largely contributed to the increased productivity after the historical N and water addition. Our study highlights the importance of plant traits and community compositions in regulating the short-term legacy effects of historical N and water input on community productivity. The positive N and water legacy effects on productivity would both last for long given the substantially changed species compositions. Long-term observation is needed for further validation of these legacy effects because of their great year-to-year variability.