title: Aridity threshold in controlling ecosystem nitrogen cycling in arid and semi-arid grasslands.
abstract: Higher aridity and more extreme rainfall events in drylands are predicted due to climate change. Yet, it is unclear how changing precipitation regimes may affect nitrogen (N) cycling, especially in areas with extremely high aridity. Here we investigate soil N isotopic values (δ(15)N) along a 3,200 km aridity gradient and reveal a hump-shaped relationship between soil δ(15)N and aridity index (AI) with a threshold at AI=0.32. Variations of foliar δ(15)N, the abundance of nitrification and denitrification genes, and metabolic quotient along the gradient provide further evidence for the existence of this threshold. Data support the hypothesis that the increase of gaseous N loss is higher than the increase of net plant N accumulation with increasing AI below AI=0.32, while the opposite is favoured above this threshold. Our results highlight the importance of N-cycling microbes in extremely dry areas and suggest different controlling factors of N-cycling on either side of the threshold.
authors.affiliation: 1] State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China [2] College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China [3].
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: 1] State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China [2] College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China [3] Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma, Norman, Oklahoma 73019, USA [4].
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Wang
authors.affiliation: 1] State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China [2] College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Dongwei
authors.initials: D
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Honghui
authors.initials: H
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Xiaotao
authors.initials: X
authors.lastname: Lü
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Yunting
authors.initials: Y
authors.lastname: Fang
authors.affiliation: 1] State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China [2] Department of Environmental Studies, University of California, Santa Cruz, California 95064, USA.
authors.forename: Weixin
authors.initials: W
authors.lastname: Cheng
authors.affiliation: 1] State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China [2] College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Wentao
authors.initials: W
authors.lastname: Luo
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Jiang
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma, Norman, Oklahoma 73019, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Shi
authors.affiliation: Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma, Norman, Oklahoma 73019, USA.
authors.forename: Huaqun
authors.initials: H
authors.lastname: Yin
authors.affiliation: 1] Department of Microbiology and Plant Biology, Institute for Environmental Genomics, University of Oklahoma, Norman, Oklahoma 73019, USA [2] Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [3] State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Jizhong
authors.initials: J
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Xingguo
authors.initials: X
authors.lastname: Han
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Edith
authors.initials: E
authors.lastname: Bai