Plant Diversity, Productivity, and Soil Nutrient Responses to Different Grassland Degradation Levels in Hulunbuir, China

The Hulunbuir grasslands are a crucial ecological security barrier in northern China. However, owing to factors such as overgrazing and climate change, it has experienced considerable degradation. Understanding the current state of grassland degradation and elucidating its impact on vegetation-soil relationships is of paramount importance. This study employed a combination of remote sensing monitoring and field surveys to assess the degradation status of the Hulunbuir grasslands. Field surveys were conducted to examine vegetation community structure and soil nutrient status at different degradation stages. Grassland degradation significantly affected the species composition of vegetation communities. As degradation intensified, species richness declined, with the proportion of Gramineae and Legume species decreasing and Asteraceae species increasing. Additionally, the proportion of annual species initially increased and then decreased. Degradation also markedly reduced aboveground, belowground, and litter biomass within the communities. Soil moisture, electrical conductivity, organic carbon, total carbon, total potassium, and hydrolyzable nitrogen contents in non-degraded areas were higher than those in severely degraded areas. Conversely, soil total phosphorus content and bulk density gradually increased with degradation. Nitrate nitrogen and ammonium nitrogen levels in severely degraded soils were significantly higher than those in non-degraded soils. Plant diversity and productivity are linearly correlated in the study area. Under the impact of degradation, soil nutrients were the primary factors influencing ecosystem productivity. Plant diversity had a significant positive impact on soil nutrients but did not significantly affect ecosystem productivity. These findings provide a theoretical basis for the effective management and restoration of degraded grasslands.