Yunhai Zhang, Michel Loreau, Nianpeng He, Guangming Zhang, Xingguo Han
The increasing availability of biologically active nitrogen (N) caused by fertilizers and atmospheric deposition has resulted in biodiversity loss in terrestrial ecosystems. Mowing (or biomass removal) is a crucial management strategy for restoring plant diversity in the face of increased N deposition/fertilization. Both N enrichment and mowing affect biodiversity and ecosystem stability, i.e., the inverse of the coefficient of temporal variability of ecosystem net primary productivity; however, it is unclear how mowing affects ecosystem stability with increasing N enrichment.
We conducted a field study (also see the photograph) with nine rates of N application (i.e., 0, 1, 2, 3, 5, 10, 15, 20, and 50 g N·m–2·yr–1) that were applied with two frequencies (two times per year versus monthly) and two mowing regimes (unmown versus mown) to investigate their effects on species richness (number of plant species m–2), species asynchrony (the asynchrony of the species response to environmental fluctuations), ecosystem stability, and the diversity–stability relationship in a temperate grassland in northern China.
During the studied period (2011–2013), the frequency of N addition had no significant effects on species richness, species asynchrony, ecosystem stability, or the relationship between species richness and ecosystem stability. But increasing the rate of N addition significantly decreased species richness, species asynchrony, and ecosystem stability. Mowing exacerbated the negative effects of N addition on ecosystem stability, but did not affect the positive relationship between species richness and ecosystem stability. Mowing increased mean ecosystem primary productivity, species richness, and species synchrony under N enrichment. Thus, infrequent mowing had positive impacts on species richness and aboveground net primary productivity, but had negative effects on ecosystem stability via a reduction in species asynchrony under N enrichment.
Our findings indicate that N enrichment can increase ecosystem productivity, but reduces species richness and ecosystem stability, and infrequent mowing can buffer the negative effects of N enrichment on biodiversity to some extent. Infrequent mowing with N enrichment may improve ecosystem productivity but reduces ecosystem stability over time.
Image caption: Ecologist at work. Photo provided by authors.