Heavy Grazing Leads to Increased Dominance of Plant and Soil Nematode Communities

Herbivore grazing plays a crucial role in grassland ecosystems, yet its comprehensive impact on plant and soil nematode diversity in desert steppe remains unclear. We assessed the impact of different grazing intensities (CK: no grazing, LG: light grazing, MG: moderate grazing, HG: heavy grazing, EG: extreme heavy grazing) on plant and soil nematode diversity in desert steppe. In the HG treatment, the diversity of plants and nematodes was the lowest and significantly lower than that in the CK treatment. Compared with CK, the Sobs, Shannon-Wiener, Inverse Simpson index, and Heip index of the plant community under HG decreased significantly by 23.78%, 37.97%, 47.43%, and 41.51%, respectively (p < 0.05). Simultaneously, the diversity indices of soil nematodes under HG also decreased significantly, being 22.2%, 40.3%, 50.9%, and 47.1% lower than those of CK, respectively. Linear and non-linear correlation analyses demonstrated a significant positive correlation between plant diversity and nematode diversity, indicating a synergistic relationship between plant communities and soil nematode communities. Pearson correlation analysis revealed that Cleistogenes songorica (Roshev.) Ohwi and Stipa breviflora Griseb. were significantly positively correlated with the herbivorous nematode genus Paratylenchus (p < 0.05), while Convolvulus ammannii Desr. was significantly positively correlated with the genus Acrobeloides (p < 0.05). These results indicated that certain specific plant species exert significant regulatory effects on specific soil nematode species. Overall, heavy grazing is detrimental to the sustainable development of grasslands. Therefore, in light of previous research in this field, maintaining grazing intensity below the level of heavy grazing (LG or MG) is the most appropriate grassland management strategy.