Responses of soil nematode community to 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 return, and soil environments. However, the belowground response pattern as well as the alterations in soil resource input and environments remain uncertain along a grazing intensity gradient. Here, we examined the response pattern of the soil nematode community (abundance, diversity, structure and functions) to grazing intensity 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 showed a hump-shaped response to increasing grazing intensity. These results indicate that the soil nematode community as well as the soil resource input and environments show a hump-shaped response to increasing yak grazing intensity. Our findings have strong implications in optimizing ecosystem structure and functions of grassland on Tibetan Plateau by managing grazing capacity.