Reduced compensatory effects explain the nitrogen-mediated reduction in stability of an alpine meadow on the Tibetan Plateau.

Abstract

Many ecosystems are facing strong perturbations such as nitrogen (N) fertilization, which can greatly alter ecosystem stability via different mechanisms. Understanding such mechanisms is critical for predicting how ecosystems will function in the face of global changes. We examined how 8yr of N fertilization with different N rates (no N addition or N addition at a low, medium or high rate) and different forms of N (ammonium, nitrate or ammonium nitrate) affected the temporal stability of the aboveground biomass of an alpine meadow on the Tibetan Plateau, and tested four mechanisms (diversity effect, mean-variance scaling, compensatory dynamics and dominance effect) that may alter stability. Compared with the control (no N addition), a high N rate did not affect the diversity effect, the mean-variance scaling or the dominance effect, but significantly decreased compensatory dynamics among species and functional groups, which contributed to the reduction in community stability of the alpine meadow. The form of N did not affect any of the four mechanisms and thus did not affect community stability. A high N rate can change community stability by altering compensatory dynamics, whereas the form of N may not have an effect.