title: Grazing intensity significantly affects belowground carbon and nitrogen cycling in grassland ecosystems: a meta-analysis.
abstract: Livestock grazing activities potentially alter ecosystem carbon (C) and nitrogen (N) cycles in grassland ecosystems. Despite the fact that numerous individual studies and a few meta-analyses had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains unclear. In this study, we performed a comprehensive meta-analysis of 115 published studies to examine the responses of 19 variables associated with belowground C and N cycling to livestock grazing in global grasslands. Our results showed that, on average, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases in microbial biomass C and N (21.62% and 24.40%, respectively). In contrast, belowground fluxes, including soil respiration, soil net N mineralization and soil N nitrification increased by 4.25%, 34.67% and 25.87%, respectively, in grazed grasslands compared to ungrazed ones. More importantly, grazing intensity significantly affected the magnitude (even direction) of changes in the majority of the assessed belowground C and N pools and fluxes, and C : N ratio as well as soil moisture. Specifically,light grazing contributed to soil C and N sequestration whereas moderate and heavy grazing significantly increased C and N losses. In addition, soil depth, livestock type and climatic conditions influenced the responses of selected variables to livestock grazing to some degree. Our findings highlight the importance of the effects of grazing intensity on belowground C and N cycling, which may need to be incorporated into regional and global models for predicting effects of human disturbance on global grasslands and assessing the climate-biosphere feedbacks.
authors.affiliation: School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200062, China.|Institute of Agricultural Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China.
authors.forename: Guiyao
authors.initials: G
authors.lastname: Zhou
authors.affiliation: School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200062, China.|Center for Global Change and Ecological Forecasting, East China Normal University, Shanghai, 200062, China.
authors.forename: Xuhui
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, 220 Handan Road, Shanghai, 200433, China.
authors.forename: Yanghui
authors.initials: Y
authors.lastname: He
authors.affiliation: School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200062, China.|Center for Global Change and Ecological Forecasting, East China Normal University, Shanghai, 200062, China.
authors.forename: Junjiong
authors.initials: J
authors.lastname: Shao
authors.affiliation: Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, 220 Handan Road, Shanghai, 200433, China.
authors.forename: Zhenhong
authors.initials: Z
authors.lastname: Hu
authors.affiliation: School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200062, China.
authors.forename: Ruiqiang
authors.initials: R
authors.lastname: Liu
authors.affiliation: School of Ecological and Environmental Sciences, East China Normal University, Shanghai, 200062, China.
authors.forename: Huimin
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Maroochydore, DC, Qld, 4558, Australia.
authors.forename: Shahla
authors.initials: S
authors.lastname: Hosseinibai
mesh_terms: D000818:Animals; D002244:Carbon; D057486:Carbon Cycle; D017753:Ecosystem; D065948:Grassland; D060434:Herbivory; D058751:Livestock; D009584:Nitrogen; D058458:Nitrogen Cycle; D006109:Poaceae; D012987:Soil
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen
keywords: CO2 emission; carbon sequestration; heavy grazing; mineralization; soil microbial biomass