Nitrogen enrichment and grazing accelerate vegetation restoration in degraded grassland patches

- N addition and grazing promote vegetation restoration in degraded grassland.
- Grazing augment the effect of N addition on grassland restoration.
- N addition enhance plant diversity in degraded grassland.

A rapid increase in grazing intensity since the 1980s has caused large areas of the Inner Mongolian grasslands to become degraded. Increasing atmospheric nitrogen (N) deposition might exert an important influence on vegetation restoration in these degraded grasslands by increasing available N and relieving N limitations on productivity. However, no previous studies have tested the assumption that increasing N deposition promotes vegetation restoration in degraded grasslands. By conducting a 4-year field restoration experiment with four N addition treatments (0, 5, 10, and 20 g N m−2 year−1) and two grazing treatments (grazed and ungrazed), we investigated the effects of N enrichment and grazing on the restoration of patches in which vegetation had been degraded. N addition significantly accelerated the restoration of vegetation-degraded grassland patches regarding both plant cover and diversity. Moderate grazing also promoted the restoration of degraded-vegetation patches in term of both plant diversity and species similarity. Importantly, the positive effects of N addition on the restoration of degraded patches may be augmented by grazing. This study demonstrate that low levels of N enrichment (or increasing atmospheric N deposition) positively impact vegetation restoration in degraded grassland patches, particularly under moderate grazing practices. Our findings provide new insights into the management of severely degraded grasslands through the regulation of N inputs and grazing practices.