Peng YF, Chen HYH, Yang YH*
PubYear : 2020
Volume :   Issue : 
Publication Name : Functional Ecology
Page number : DOI: 10.1111/1365-2435.13622
Abstract : 

1. Ecosystem productivity usually exhibits first increase and then saturated response to increasing nitrogen (N) additions, yet the broad‐scale pattern and potential drivers of the N saturation threshold are little investigated.
2. By synthesizing N addition experiments with at least four N‐input levels from the global grasslands, we applied the quadratic‐plus‐plateau model to fit the above‐ground net primary productivity (ANPP)–N rate relationship, and estimated the saturation threshold for N rate (critical N rate, N_CR) and ANPP (maximum ANPP, ANPP_max) from the inflection point where ANPP no longer statistically increased with N rate for individual experiments. Based on these estimations, we investigated the spatial pattern and driving factors of N_CR and ANPP_max.
3. The mean N_CR and ANPP_max were 15.0 and 477.0 g m^-2 year^-1, respectively, but varied substantially among single‐site experiments. Management strategies (e.g. biomass harvest, different N forms and addition frequencies) minimally influenced both parameters. Structural equation models demonstrated that the spatial differences in N_CR and ANPP_max were mainly explained by aridity index, and soil carbon (C)/N ratio also predicted the variation in N_CR.
4. Given that grasslands are important not only for the trend and variability of the land C sink but also for the maintenance of pasture yield, the pattern and controls of N_CR and ANPP_max, as revealed by the current study, are crucial for constructing robust predictions of C sink capacity and improving N fertilizer management in grasslands.