Non-Linear Responses of the Soil Nematode Community Along a Gradient of Yak Grazing Intensity in an Alpine Meadow

Livestock grazing dramatically impacts the belowground community in grasslands by altering resource input from plants, dung and urine and soil environments. However, the belowground response pattern as well as the alterations in soil resource input and environments along a grazing intensity gradient, remain uncertain. We examined the response pattern of the soil nematode community (abundance, diversity, structure and function) to grazing by performing a 5-year field manipulation experiment with four levels of yak grazing intensities in a Tibetan alpine meadow. Moderate grazing (i.e., 2 yak/ha) supported the highest abundances of all nematodes, plant feeders and omni-carnivores and maintained the most closely interspecific interactions within the nematode community. Grazing intensity may affect the belowground community via compensatory growth of forages and bottom-up trophic effects from living roots to the soil micro-food web. Furthermore, moderate grazing increased the functional metabolic footprint index of the nematode community, activated the root energy channel, and maintained the balance between the bacterial and fungal channels, which can optimize soil nutrient cycling . The model averaging results showed that the response of the soil nematode community to grazing intensity was mainly related to the alteration of soil moisture, which also non-linearly responded to increasing grazing intensity. These results indicate that the soil nematode community as well as the soil resource inputs and environments show a hump-shaped response to increasing yak grazing intensity. Our findings have strong implications for grazing capacity determination and grassland management to optimize ecosystem structure and functions on the Qinghai-Tibetan Plateau.