COS 127-5
Increased rainfall variability and nitrogen fertilization accelerate nutrient cycling in a restored prairie
Climate model projections suggest that precipitation patterns will become more variable as the planet warms, increasing the frequency of large rainfall events and prolonged drought. These changes in precipitation variability can potentially strongly influence plant community composition, but also ecosystem processes like litter decomposition and nutrient cycling. Concurrently, chronic anthropogenic nitrogen deposition has become a leading factor of global change in many terrestrial ecosystems and strongly affects community structure and function. Using a factorial combination of partial rainout shelters and a slow-release nitrogen fertilizer, we examined how more variable rainfall patterns and elevated nitrogen availability influenced litter quality, decomposition, and nitrogen loss of two dominant tallgrass prairie species: Schizachyrium scoparium and Solidago canadensis. Litter from each of our four treatment combinations was decomposed in both its plot of origin and in plots of the three other treatment combinations, allowing us to isolate the effects of our treatments during litter production and during the decomposition process. Litter was incubated in the field for 60, 210, or 365 days starting in December 2012.
Results/Conclusions
Overall, decomposition and nitrogen loss were more strongly influenced by rainfall variability and nitrogen addition during decomposition than by rainfall or nitrogen treatments during litter formation. Nitrogen addition during litter production acted to reduce C:N ratios, but also increased mass and nitrogen dynamics of litters independently of changes in this ratio. In contrast, increased rainfall variability during litter production increased C:N ratios. Nitrogen addition and increased rainfall variability during decomposition accelerated decomposition and nitrogen loss, particularly for S. canadensis after 365 days of incubation. In all cases, litter of S. canadensis decomposed faster, lost nitrogen more quickly, and was more responsive to our treatments than litter of S. scoparium. These results suggest generally faster nutrient cycling in future grasslands exposed to increased rainfall variability and chronic nitrogen addition.