Degradation stage effects on vegetation and soil properties interactions in alpine steppe

In recent decades, overgrazing and the warming and drying climate have resulted in significant degradation of alpine grasslands in the source region of the Yellow River. However, research into the relationships between vegetation and soil properties has mainly focused on an overall degradation stage, and few studies have investigated which soil properties can impact vegetation change at different stages of degradation. Vegetation and soil properties were observed in the field and measured in the laboratory for different predefined stages of degradation for alpine grassland in Maduo County in the source region of the Yellow River. Results show that: 1) the aboveground and belowground biomass, soil organic carbon, total nitrogen, nitrate, and ammonia content did not decrease significantly from the intact to moderate degradation stage, but decreased significantly at severe and very severe stages of degradation; 2) dominant plant species shifted from gramineaes and sedges to forbs; 3) the species richness and Pielou evenness indices decreased significantly at the very severe degradation stage, the Shannon-Wiener diversity index increased at the slight and moderate degradation, but decreased at the severe and very severe degradation stages; 4) soil bulk density was the strongest soil driver for changes in the plant biomass and community diversity at the intact, slight and moderate degradation stages, whereas soil organic carbon and nitrate nitrogen content were the main driving factors for changes in plant biomass and diversity at the severe and very severe degradation stages. Our results suggest that there may be different interactions between soil properties and plants before and after moderate stages of degradation.