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 18 months 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 12 months for high‐quality litter species. Dung reduced N immobilization after 6 months and did not affect subsequent release in low‐quality litter species, and promoted N release after 6 and 12 months in high‐quality litter species. Regardless of litter quality, dung increased P release after 6 and 12 months. 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.
Nutrient resorption from senescing leaves is an important plant nutrient conservation mechanism. Effects of functional groups on nitrogen resorption efficiency (NRE) are well known in woody perennials in forest ecosystems, but less is known from other ecosystems. We investigated green and senesced leaf nitrogen (N) concentrations of different functional groups in a Tibetan alpine meadow. We found legumes contained higher N in green leaves, with no significant differences in N between graminoids and forbs. Graminoids contained the lowest amount of N in senesced leaves, followed by forbs and legumes. NRE was higher in graminoids, with no significant difference between legumes and forbs. Our results showed that level of N was related to resorption in this ecosystem, with NRE decreasing as green leaf N concentration increased, regardless of the functional group. Furthermore, we found differences in N concentration in senesced leaves resulted from differences in both green leaf N concentration and NRE across functional groups. Our findings highlight that the ability to minimize N loss by both reducing the N concentration in senescing leaves and increasing NRE could explain the dominance of graminoids in this alpine meadow. Our results indicate that change in the dominance of different functional groups could influence soil N cycling in this ecosystem.
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