Grazing depresses soil carbon storage through changing plant biomass and composition in a Tibetan alpine meadow
Sun, D.S.,Lanzhou Univ. (China). MOE Key Lab. of Arid and Grassland Ecology | Wesche, K.,Senckenberg Natural History Museum, Goerlitz (Germany). Botany Dept. | Chen, D.D.,Lanzhou Univ. (China). MOE Key Lab. of Arid and Grassland Ecology | Zhang, S.H.,Lanzhou Univ. (China). MOE Key Lab. of Arid and Grassland Ecology | Wu, G.L.,Northwest A and F Univ., Yangling (China). State Key Lab. of Soil Erosion and Dryland Farming on the Loess Plateau | Du, G.Z.,Lanzhou Univ. (China). MOE Key Lab. of Arid and Grassland Ecology | Comerford, N.B.,University of Florida, Gainesville (USA). Soil and Water Science Dept.
A three-year field study (2005-2007) was conducted in Tibetan alpine meadow to address the responses of surface soil (0-15 cm) organic carbon (SOC) storage in the plant growing season (from May to September) to varying grazing intensity (represented by the residual aboveground biomass, with G0, G1, G2, and G3 standing for 100%, 66%, 55%, and 30% biomass residual, respectively), and to explore whether grazing-induced vegetation changes depress or facilitate SOC storage. Our results showed that: (i) Higher grazing intensity resulted in lower biomass of grasses and sedges, lower root biomass, and in a change in plant community composition from palatable grasses and sedges to less palatable forbs. (ii) Increased grazing reduced the SOC content and storage with only G3 showing an SOC loss during the plant growing season. (iii) Soil organic carbon storage exhibited a highly positive correlation with the residual aboveground biomass and root biomass. Our results imply that a grazing-induced reduction in plant biomass productivity and changes in species composition would depress soil carbon storage, and that an increase in grazing pressure can lead to a gradual change of alpine meadow soils from being 'carbon sinks' to become 'carbon sources'.
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