Enhanced Community Production rather than Structure Improvement under Nitrogen and Phosphorus Addition in Severely Degraded Alpine Meadows

Fertilization is a common management measure for the restoration of degraded grasslands. In order to investigate whether fertilization can improve the severely degraded alpine meadows, we conducted a fertilization experiment on the Tibetan Plateau that began in 2008. The treatments were nitrogen (N) addition alone (50 kg N ha −1 year −1 , LN; 100 kg N ha −1 year −1 , HN) or combined with phosphorus (P) fertilizer [(50 kg N + 50 kg P) ha −1 year −1 , LN+P; (100 kg N + 50 kg P) ha −1 year −1 , HN + P] in a severely degraded alpine meadow. Eleven consecutive years of N and P fertilization did not significantly change plant species richness, while fertilization reduced the plant species diversity index, with the most significant reduction in HN and HN + P treatments. LN + P and HN + P treatments greatly increased community coverage and aboveground biomass, while N addition alone, especially the HN treatment, significantly reduced community coverage and aboveground biomass. Fertilization had no effect on edible pastures, while N and P fertilization significantly increased the biomass of forbs. The proportion of forbs to total aboveground biomass was more than 90%, and fertilization had no effect on this proportion. This shows that forbs still have an absolute advantage in the community. In addition, HN, LN + P, and HN + P treatments significantly reduced ecosystem stability. Community aboveground biomass was greatly enhanced in the N and P fertilization treatments, and this was beneficial for the ecosystem quality and soil hydrological functioning. However, fertilization treatments did not improve the community structure with either N addition alone or combined with P fertilizer, which was of little significance in providing forages for the sustainable development of livestock husbandry. To improve the structure of severely degraded alpine grasslands, it is necessary to combine other measures such as cutting the roots of forbs, fencing, or reseeding.