Effects of fertilization and enclosure on the temporal stability of above-ground net primary productivity in an alpine meadow of the Tibetan Plateau

Changes in grassland utilization (i.e., fertilization and enclosure) can influence the temporal stability of aboveground net primary productivity (ANPP) by altering ANPP and its temporal variability. In addition, changes in species richness and asynchrony can also drive changes in ANPP stability. Ecologists have focused on investigating the effects of fertilization or enclosure on ANPP stability via different ecological pathways in grassland ecosystems, but the mechanisms underlying these effects remain unclear. Here, we conducted a factorial experiment of fertilization (multiple additions of nitrogen, potassium, and phosphate) with all-year enclosure treatments (enclosure and fertilization plus enclosure) for four consecutive years in a grazed alpine meadow located in the Gannan region in the eastern part of the Tibetan Plateau. We aimed to investigate the mechanisms underlying the responses of ANPP stability to fertilization and enclosure. The results revealed that enclosure reduced ANPP stability, and this reduction was driven by the relative changes in ANPP and its variability and was closely associated with decrease in species richness and asynchrony. Furthermore, although no direct negative effects of fertilization on ANPP stability were observed, fertilization decreased the species richness and increased ANPP, which may translate into reductions in ANPP stability in the future. Our results indicated that winter grazing would contribute towards the maintenance of ANPP stability in an alpine meadow community, whereas year-round enclosure, regardless of fertilization, would deteriorate ANPP stability. Therefore, it is imperative to carefully evaluate the potential mechanisms influencing biodiversity and ecosystem functioning in grassland utilization and management in future research.