Water Manipulations Altered Grazing Effects on Carbon Exchange in a Desert Steppe

doi:10.3969/j.issn.1000-6362.2019.12.001

Abstract

Abstract: Based on a long term grazing experiment (10 years) that includes no grazing (CK), light grazing (LG) and heavy grazing (HG) over a Stipa breviflora desert steppe in Siziwang, Wulanchabu, Inner Mongolia, China, a manipulative experiment of water input was conducted during 2012?2013. The grazing plots were treated as the block factor for nested water treatments. We aimed at exploring the responses of net ecosystem exchange (NEE), ecosystem respiration (RE) and gross ecosystem exchange (GEE) of carbon under two water additions: irrigation vs no-irrigation. We found that: (1) the desert steppe was a net carbon sink. Irrigation indirectly increased RE and the ecosystem carbon sink by elevating soil volumetric water content (Vwc) without grazing (P<0.01). NEE, RE and GEE were found to be more sensitive to Vwc due to irrigation (P<0.001). (2) The differences in NEE, RE and GEE among the grazing treatments were not significant under no-irrigation treatment, whereas positive deviations of ΔNEE and ΔGEE with grazing after August were significantly greater than the negative deviations before August (P<0.001). (3) The interactive contributions from irrigation and grazing treatments produced no significant effect on NEE, RE and GEE, but increased Vwc under grazing that enhanced ecosystem carbon sink and RE. When the grazing intensity was explored, both the magnitudes and changes of RE and GEE with Vwc at grazed sites were higher than those at no grazing plots (0.26 and 0.61, respectively), indicating that grazing resulted in a decrease in the sensitivity of carbon exchange to Vwc.

Key words: Irrigation, Soil volumetric water content, Grazing intensity, Desert steppe, Ecosystem carbon exchange

LIU Qian, ZHANG Fang-min, CHEN Ji-quan, ZHAO Xiao-han, JING Yuan-shu. Water Manipulations Altered Grazing Effects on Carbon Exchange in a Desert Steppe[J]. Chinese Journal of Agrometeorology, 2019, 40(12): 737-746.

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