Restoration effects of fertilization and grazing exclusion on different degraded alpine grasslands: Evidence from a 10-year experiment

Abstract Understanding the changes in vegetation parameters and soil nutrients in different stages of recovery is crucial for assessing and restoring degraded grasslands. Different degraded grasslands may respond differently to fertilization and grazing exclusion due to the change in species composition, while research in this aspect is still lacking. Two lightly (LD) and one heavily degraded (HD) plots were set up, with one LD plot under grazing exclusion (LDGE), aiming to investigate the effects of these management measures on forage restoration under different degraded alpine grasslands. Nitrogen (N) addition showed a tendency to reduce community cover and aboveground biomass in LD plot, but had no effect in LDGE and HD plots. N and phosphorus (P) combined additions (N + P additions) greatly enhanced the community cover and aboveground biomass, suggesting P addition can reverse the negative effects of N addition. In LDGE plot, all fertilization treatments enhanced the growth of palatable species, and only N + P additions increased it in LD plot, while fertilization did not improve palatable species in HD plot. Additionally, grazing exclusion promoted fertilization effects, and the effects of fertilization on palatable species were much more pronounced in LDGE plot than those in LD plot. The effects of nutritious enrichment were primarily controlled by soil pH change, while they were also regulated by the changes in soil nutrient availability in LD plot. These results suggest that grazing exclusion and fertilization (especially N + P additions) can additively enhance community production of the lightly degraded alpine grasslands, while the structure of heavily degraded alpine grasslands cannot be restored by nutrition enrichment due to the forbs-dominated structure although plant production was greatly enhanced, and other measures should be combined to restore the community structure in heavily degraded alpine grasslands.