Herbivore Dung Deposition Enhances the Decomposition of Fine Root Litter in a Tibetan Alpine Meadow

The effects of grazers’ dung deposition on leaf litter in Tibetan alpine meadows are well-established: generally having a positive influence on the decomposition process. However, little is known about how dung deposition influences root litter decomposition belowground, given that roots account for approximately a quarter of plant biomass in these meadows, which is a notable knowledge gap. Our objective was to investigate the effects of yak (the system’s primary grazer) dung on fine root litter decomposition. We conducted a root litter decomposition experiment in an alpine grassland over 2 yr, with and without experimental yak dung deposition. We measured root litter mass loss, chemical composition, and extracellular enzyme activity at intervals of 0.5, 1, 1.5, and 2 yr. After 2 yr, sites with dung application demonstrated faster root litter mass loss (8%), a greater decomposition rate constant ( k ), and increased root litter nitrogen and phosphorus. At the 0.5 yr, sites with dung application demonstrated minimal outcomes on litter enzymes associated with decomposition, with only higher acid phosphatase (AP) activity. However, during 0.5–2 yr, all measured litter enzymes were affected by dung application, with higher β-1,4-glucosidase (BG) activity, and lower activities of both AP and N -acetyl-β- d -glucosaminidase (NAG). Our results suggest that dung application had no effects on fine root decomposition at early stage (0.5 yr), possibly due to the buffering effect of the soil layer. In contrast, dung application could accelerate fine root decomposition at middle stage (0.5–2.0 yr), mainly by enhancing BG activity associated with cellulose decomposition due to alleviating nutrient limitation on microbes. As the overall number of yaks in the Tibetan grasslands is anticipated to rise in the future, this could exert a profound influence on the ecosystem functioning by promoting the decomposition of fine roots.