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Effect of change of plant community composition along degradation gradients on water conditions in an alpine swamp wetland on the Qinghai-Tibetan Plateau of China
青藏高原高寒沼泽湿地在退化梯度上植物群落组成的改变对湿地水分状况的影响

Keywords: alpine wetland,degradation,photosynthetic physiology trait,plant community,water use efficiency
高寒湿地
,退化,光合生理特征,植物群落,水分利用效率

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Aims Wetlands degradation has drawn increased concern recently.Many researchers have reported the changes of plant communities and the relevant degradation mechanism of wetlands.However,few studies have explored the effects of plant community change on the water conditions of swamp meadow.Our objective was to investigate how change of alpine swamp meadow along degradation gradients affects its water conditions.Methods The study was conducted at the Research Station of Alpine Meadow and Wetland Ecosystems of Lanzhou University(Maqu Branch Station)(33°39’ N,101°53’ E).We examined 47 species(15 families) selected from a degradation gradient of alpine swamp meadow.Net photosynthesis rate(Pn),transpiration rate(Tr) and stomatal conductance(Gs) were measured simultaneously with a portable gas exchange system LI-6400(Li-COR,Lincoln,NE,USA).Measurements were performed from 9:00 am to 12:00 am on clear days in mid-July and mid-August,using photosynthetically active radiation(PAR) = 1 800 μmol.m-2.s-1 and flow = 750 μmol.s-1.The value of water use efficiency(WUE) was determined by Pn/Tr.We also investigated the cover of different functional groups(grasses,sedges,legumes and other forbs) at different degradation levels.Important findings The photosynthetic physiology traits were different among species and functional groups(p < 0.01).The sequence of Pn values of functional groups was grasses > sedges > legumes and other forbs,and WUE was sedges > grasses > legumes and other forbs.Species composition of the plant community had been changed due to the degradation of the swamp meadow.The abundance of forbs increased with degradation.WUE was lower for forbs than other functional groups,which implied that more soil water is transpired,exacerbating the drought condition of degraded meadows.Successful restoration requires protection and replenishment of the typical native species.

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