短期增温对青藏高原高寒草甸植物群落结构和生物量的影响

Short-term effects of temperature enhancement on community structure and biomass of alpine meadow in the Qinghai-Tibet Plateau

采用增温棚模拟增温的方法,对比研究了青藏高原腹地典型高寒草甸和沼泽草甸在两种增温梯度条件下植物群落结构及植物生长对温度升高的初期响应。由于开顶式生长室(OTC)的增温作用,在整个生长季内,沼泽草甸月平均气温分别较对照提高2.98℃(OTC1)和5.52℃((OTC2),20cm处土壤水分分别减少了2.45%(OTC1)和3.44%(OTC2);高寒草甸月平均气温分别比对照升高了2.59℃(OTC1)和5.16℃(OTC2)。20cm处土壤水分分别减少了1.83%(OTC1)和7.71%(OTC2)。受温度升高及土壤含水量减少的影响,模拟增温2个生长季后,与对照样地相比,群落种群高度、密度、盖度、频度和重要值发生变化,群落结构也发生一定变化。增温处理使高寒草甸禾草和莎草盖度减少,杂草盖度增加,而使沼泽草甸中禾草和莎草盖度增加,杂草盖度减少。增温后,两种草甸总生物量均增加,但大幅度的增温条件抑制了高寒草甸的这种促进作用,而促进了沼泽草甸的这种促进作用。两种草甸的地下生物量主要分布在土壤表层,模拟增温使得高寒草甸的生物量分配格局向深层转移,但不明显;而使沼泽草甸生物量明显的趋向深层土壤中转移。

The aim of this study was to assess the initial effects of warming on the community structure and biomass allocation of alpine swamp meadow and alpine meadow,two most widespread ecosystem types in the Qinghai-Tibet Plateau.The air and upper layer soil temperatures were passively enhanced by using open-top chambers（OTCs） with two heights.The air temperature was clearly increased by 2.98℃ in 40cm high OTCs（OTC1） and 5.52℃ in 80cm high OTCs（OTC2） in alpine swamp meadow,and the soil water content decreased by 2.45%（OTC1） and 3.44%（OTC2）,respectively.While the air temperature was increased by 2.59℃（OTC1） and 5.16℃（OTC2） in alpine meadow,and the soil water content decreased by 1.83%（OTC1） and 7.71%（OTC2）,respectively.With the warming and drying effects,some changes in the vegetation community structure were observed.The population height,density,coverage,relativity,and important value of each plant community responded differently to warming.In alpine meadow,important values of three species in OTC1 were increased,and five species decreased.The importance values of Saussurea eopygmaea and Primula forbesii decreased significantly,while the values of Kobresia pygmaea and Littledalea racemose increased significantly.The warming effects in OTC2 accelerate the development of singularity,the important values of Kobresia pygmaea and Primula forbesii decreased significantly,while the values of Halerpestes tricuspis and Carex atrofusca increased significantly.In alpine swamp meadow,important values of Kobresia tibetica and Kobresia humilis in OTC1 were increased,while the values of Ranunculus decreased significantly.The warming effects in OTC2 accelerate the dominances of Kobresia tibetica and Kobresia humilis,and the important value of Ranunculus also increased.Compared to each control plots,warming in alpine meadow caused the coverage of graminoid and sedge decreased,coverage of forbs increased;while in alpine swamp meadow were the reverse.Warming caused the biomass of standing dead and litter in the OTCs were lower than that in the control plots,this means that the warming delayed the senescence and death of plants,and biomass of standing dead and litter in higher warming conditions in OTC2 plots were even less than that in OTC1 plots.The coverage of alpine graminoid and sedge in alpine meadow significantly decreased,while the coverage of forbs increased.In alpine swamp meadow,the coverage of graminoid and sedge increased,while the coverage of forbs decreased.Warming increased the total biomass of both meadows,and higher warming in OTC2 accelerated and prohibited this trend in swamp meadow and alpine meadow,respectively.Warming made the biomass allocation in two meadows transferred to the deeper soil layer to adjust the warming and drying conditions.The four typical species in two meadows further illustrated the community structure and plant growth in response to artificial warming.