title: The effects of grazing and watering on ecosystem CO2 fluxes vary by community phenology.
abstract: Grazing profoundly influences vegetation and the subsequent carbon fluxes in various ecosystems. However, little effort has been made to explore the underlying mechanisms for phenological changes and their consequences on carbon fluxes at ecosystem level, especially under the coupled influences of human disturbances and climate change. Here, a manipulative experiment (2012-2013) was conducted to examine both the independent and interactive effects of grazing and watering on carbon fluxes across phenological phases in a desert steppe. Grazing advanced or delayed phenological timing, leading to a shortened green-up phase (GrP: 23.60 days) in 2013 and browning phase (BrP: 12.48 days) in 2012 from high grazing, and insignificant effects on the reproductive phase (ReP) in either year. High grazing significantly enhance carbon uptake, while light grazing reduce carbon uptake in ReP. Watering only delayed the browning time by 5.01 days in 2013, producing no significant effects on any phenophase. Watering promoted the net ecosystem exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) only in the GrP. When calculating the yearly differences in phenophases and the corresponding carbon fluxes, we found that an extended GrP greatly enhanced NEE, but a prolonged ReP distinctly reduced it. The extended GrP also significantly promote GEP. Increases in growing season length appeared promoting ER, regardless of any phenophase. Additionally, the shifts in NEE appeared dependent of the variations in leaf area index (LAI).
authors.affiliation: International Center for Ecology, Meteorology, and Environment, Nanjing University of Information Science and Technology, Nanjing 210044, China; Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Juanjuan
authors.initials: J
authors.lastname: Han
authors.affiliation: Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Linghao
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA.
authors.forename: Housen
authors.initials: H
authors.lastname: Chu
authors.affiliation: China and State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng, Henan 475004, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Miao
authors.affiliation: Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Shiping
authors.initials: S
authors.lastname: Chen
authors.affiliation: CGCEO/Geography, Michigan State University, East Lansing, MI 48824, USA. Electronic address: jqchen@msu.edu.
authors.forename: Jiquan
authors.initials: J
authors.lastname: Chen
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000032:analysis*; D002681:China; D003889:Desert Climate; D005247:Feeding Behavior; D065948:Grassland; D011897:Random Allocation; D012756:Sheep; D013997:Time Factors; D014867:Water / Q000032:analysis
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Carbon; Desert steppe; Grazing; Human disturbances; Phenology; Water