Nitrogen and phosphorus change the early natural vegetation restoration in degraded Phaeozems of gullies

The influence of nutrients during natural vegetation restoration (NVR) in complicated landscapes and hydrologic con-ditions has often been debated. This study aimed to clarify how nitrogen (N) and phosphorus (P) runoff influences plant biomass and biodiversity during early restoration stages in gullies. In this study, the influence of runoff contain-ing N, P, and N + P on the biomass and diversity of ten predominant herbaceous species was simulated in two de-graded Phaeozems of gullies by under controlled conditions for two years. Increasing N in runoff increased the biomass in both low-degradation Phaeozems (LDP) and high-degradation Phaeozems (HDP), and N input could in-crease the competitive ability of No-Gramineae (NG) and constrain G biomass in the second year. N and P increased the biomass by increasing the species abundance and individual mass but not the diversity. N input typically decreased biodiversity, while P input influenced the dynamics of biodiversity was nonmonotonic increased or decreased. Com-pared with sole N input, additional P accelerated the competition of NG, restrained G mass, and decreased the total biomass in LDP, while increasing the total biomass in HDP in the first year. However, additional P input did not change the N effects on biodiversity in the first year, while high P input improved the herbaceous diversity in the second year of gullies. Generally, N in runoff was the key factor influencing NVR, especially for biomass in early NVR stages. The P dose and the ratio of N:P in the runoff were the main determinants of P mediation on the N effect on NVR.

Automated summary

This study aimed to clarify the influence of nitrogen (N) and phosphorus (P) runoff on plant biomass and biodiversity during early restoration stages in gullies. The results showed that N input increased plant biomass but decreased biodiversity, while P input had mixed effects on biodiversity but increased biomass. N was the key factor influencing vegetation restoration, while the ratio of N:P in the runoff determined the mediation of P on N effect.