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N deposition can accelerate the degradation succession from grasses- and sedges-dominated plant communities into forbs-dominated ones in overgrazed alpine grassland systems on Qinghai-Tibetan Plateau
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  • Hao Shen,
  • Shikui Dong,
  • Antonio DiTommaso,
  • Jiannan Xiao,
  • Yangliu Zhi
Hao Shen
Beijing Normal University
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Shikui Dong
State Key Joint Laboratory of Environmental Simulation and Pollution Control
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Antonio DiTommaso
Cornell University
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Jiannan Xiao
Beijing Normal University
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Yangliu Zhi
Beijing Normal University
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Abstract

Alpine grasslands are sensitive to grazing and atmospheric deposition of nitrogen (N). With the increase of N deposition, experimental investigations of the effects of grazing on alpine grassland vegetation with the background of N deposition are scarce. In this study, we examined the effects of overgrazing and overgrazing with N deposition on eco-physiologies of alpine grassland plants at the functional group level. We found that both overgrazing and overgrazing with N deposition obviously changed species composition and the dominance of three plant functional groups (PFGs) in alpine meadow and alpine steppe. Under overgrazing and overgrazing with N deposition treatment, forb tended to be predominant in the whole plant community, while grass and sedge dominance was obviously decreased. In addition, we found that the underlying eco-physiological processes that lead to forb-dominant were different under overgrazing and overgrazing with N deposition. Overgrazing with N deposition obviously tended to increase forb dominance both directly by selective herbivory and indirectly by enhancing forb photosynthetic capacity. Our results suggested that long-term overgrazing with N deposition will lead to a more favorable living environment for forbs, making the grassland community of alpine grasslands on the Qinghai-Tibetan Plateau likely shift to forb-dominant in the future.