Interacting effects of yak dung deposition and litter quality on litter mass loss and nitrogen dynamics in Tibetan alpine grassland

The effects of grazing-induced dung deposition on plant growth and soil attributes are well established, but little is known about dung effects on litter decomposition. Here, we tested effects of yak dung on litter decomposition and nutrient content in a Tibetan alpine meadow. We incubated litter of four common alpine meadow species using litter bags in the field. Two low-quality species (Kobresia capillifolia and Elymus nutans) with low nitrogen (N), high C/N and Lignin/N, and two high-quality species, (Saussurea nigrescens and Thermopsis lanceolata) were incubated in monoculture with and without dung addition. Mass loss of leaf litter, fibre fraction (cellulose, hemi-cellulose and lignin), N and phosphorus (P) were measured after 6, 12 and 18months of incubation in the field. Dung addition significantly increased decomposition constants for low-quality litter species, but not for high-quality litter species. Dung addition promoted cellulose and hemi-cellulose loss, but lignin loss was not affected by dung addition, except after 12months for high-quality litter species. Dung reduced N immobilization after 6months and did not affect subsequent release in low-quality litter species, and promoted N release after 6 and 12months in high-quality litter species. Regardless of litter quality, dung increased P release after 6 and 12months. Our results suggest grazing-induced dung deposition may accelerate C and nutrient turnover, primarily through increasing the mass loss of low-quality litter, P release from litter and N release from high-quality litter. The mechanisms underlying the effects of dung deposition need to be clarified in future studies.