| Rapid land degradation and desertification have taken place in grassland and meadow of many sites in the world,by overgrazing due to very high stocking rates to sustain development of production and economy of human.As a result,there is degradation and desertification in some places of Alpine meadow ecosystem in China. Hence it is key problem that understand the degradation progress and restoration mechanism of an ecosystem.Therefore,the study of degradation and restoration on grassland or meadow is one of the hot issues in ecology.Our study was to understand the effect of grazing on aboveground biomass allocation,productive,productive allocation of different functional group and community structure with three levels, which was species,functional group and community.We compared the effect of grazing on biomass allocation of 26 species of plants in alpine meadows of the Tibetan Plateau,to address the following questions.1)Does grazing significantly affect biomass allocation of these species? 2)If so,what are the general patterns of response? 3)Does this effect differ among species and functional groups within same community? 4)Does grazing affect the biomass allocation of the plant community? 5) Does grazing affect the productive and productive allocation of different functional group of the plant community? 6)Does grazing affect the structure of the community? From June to September in 2005 to 2007,we sampled 25-30 individuals (above-ground parts)of each species from ten random plots of each of two treatments—long-term grazing and grazing exclusion for 7 years.When sampling,we considered the fruiting phenology of each species.We divided species into four functional groups—legumes,unpalatable forbs,palatable forbs and graminoids.Each individual was dissected into reproductive organs,stems,and leaves,dried to constant weight for 48h at 80℃,and weighed with a Sartorius Balance(10-4g).Individual biomass(IB)was calculated as the sum of these biomass components.We then calculated reproductive allocation(RA)=reproductive organ biomass/IB,stem allocation(SA)=stem biomass/IB,and leaf allocation(LA)=leaf biomass/IB.We used independent-samples t-tests to test the difference of IB(RA,SA and LA) between two grazing treatments for each species.We also determined above-ground biomass and biomass allocation for both grazed and grazing exclusion treatments.We sampled ten square(0.5m×0.5m)in ten randomly plots of each treatments—long-term grazing and grazing exclusion for 6 years.We divided species into five functional groups—legumes,cyperaceous,unpalatable forbs,palatable forbs and grasses.We measured species richness,abundance(number of individual),community height and cover in each square,and above-ground biomass according to function groups. Sampled were dried at 80℃,and weighed with a Sartorius Balance at the nearest 10-3 g.The result showed as following,ⅰ)Grazing significantly affected individual biomass and biomass allocation of the study species,ⅱ)Generally,grazing decreased average individual biomass while increasing reproductive allocation for most species. Average stem allocation tended to decrease in response to grazing for most species,ⅲ) The effect of grazing on biomass and biomass allocation differed among species and functional groups.Reproduction allocation tended to increase for all functional group. Stem allocation tended to decrease all functional group.Leaf allocation tended to increase for unpalatable forbs and decrease for palatable forbs,legumes and graminoids,ⅳ)At the community level,reproductive allocation and leaf allocation increase because of grazing,and stem allocation decreased,ⅴ)Grazing results for significant reduce in community productivity.Functional groups are different in responses to grazing,graminoids(cyperaceous and grasses)biomass significant reduced from average 76.6%to 57.4%,while legumes,palatable forbs and unpalatable forbs,ⅵ)The highest of plant community reduced from 46.8 to 22.4. Biodiversity and individual density increased,biodiversity was increased from average 26.5 species each square to 30.9 and abundance was increased from average 215.7 each square to 304.6.Total percentage coverage did not significant difference between grazing and non-grazing plots. |
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