Divergent interactive impacts on productivity and functional diversity from fluctuated snowfall and continuous...

Nitrogen pollution effects on plant communities are well documented, however, most field researches on nitrogen pollution have failed to account for extraneous environmental factors and the interaction among changes in multiple stressors. In this study, we show the effect of eutrophication via nitrogen deposition and altered snowfall on the productivity and traits space of an Inner Mongolian grassland where is recovered from abandoned farmland for 13 years. This multi-year factorial experiment allowed us to test the independent and interactive effects of nitrogen and snow deposition within this ecosystem. We simulated nitrogen pollution (added nitrogen) and extremely snowfall (added snow) to each plot for three years. After the third year, only nitrogen was added for the next two years to keep a continuous N-pollution condition. We measured changes in aboveground net primary production (ANPP), occupied functional traits space (OFS), and the centroid range of OFS (spatial traits variability, STV) at community level. Our results showed that the interaction between continuous nitrogen pollution and fluctuated snow have different effects on ANPP and functional diversity (indicated by OFS and STV). In nitrogen and nitrogen combined with snow treatment, its ANPP increased, while its OFS increased in 2010 but decreased in 2012 and 2014. Increases in snow did not affect ANPP and OFS, but significantly impacted spatial traits variability. Snow addition corresponded with decreasing the spatial traits variability in 2010, followed by increasing in 2012 and 2014. The results indicate N-Pollution on grassland ecosystem cannot be interpreted only by ANPP, especially when N-pollution interacted with changes of other extremely stressors such as snowfall.