Response Of Plant Diversity And Ecosystem Function To Plant Species Removal In An Alpine Meadow

The topic of biodiversity and ecosystem functioning is the center of community ecology.Based on field observational studies and artificial grassland experiment started from 1980 s,a large number of studies documented the importance of biodiversity in promoting ecosystem functioning and raised various hypotheses to explore the underlying mechanisms,which resulted a common sense conclusion that the loss of species diversity will significant impact on ecosystem functioning and services.However,whether the response of biodiversity and ecosystem functioning to realistic loss of plant species diversity consistent with this prediction remains larger uncertainty,because: i)observational studies cannot distinguishing effect of diversity loss from effect of co-varied abiotic factors on ecosystem functioning;ii)process and pattern of artificial assembled community inconsistent with that of natural community,which dominated by few species companied with large number of infrequent species;and ii)the effect of species addition did not necessarily consistent with species loss on ecosystem functioning.Considering on these inconsistency,there is a need to rethinking and test whether and how plant diversity and ecosystem functioning in response to realistic loss of plant species,especially in the light of advance in trait ecology that highlights importance of species attributes as well as intraspecific trait variability in community assembly and ecosystem functioning.With very high diversity within plant community and low variation in diversity and soil factors between plots as well as sensitively response to climate change,the alpine meadows in Tibetan Plateau provide ideal natural laboratory to test how realistic loss of plant species diversity impacting ecosystem functioning.Based on these background and plant species loss in response to climate change and grazing,in this thesis,I reported the results from my six-year's experiment of plant species removal.Briefly,we conducted a set of plant species removal experiment,which removal of dominated sedge species,tall grass species,tall forb species,mediate-height forb species and short forbs species in a typical design of randomized block experiment started from 2013 and lasted until 2018.We aim to reveal the response of plant diversity and ecosystem functioning to realistic loss of plant species by answering a set of fundamental questions in community ecology,such as the importance of niche differentiation,biodiversity and productivity stability,plant-soil feedback,in response to removal of different species.Comparing to relevant studies,our preliminary results highlighted four novel points.Firstly,species removal generally increased the intraspecific trait variability(ITV)in all measured traits.The difference in plant trait diversity between plots attribute mostly to ITV rather than to species turnover,with ITV pronouncedly contribution to trait variation between plots for plant height,leaf N and P but less important to specific leaf area and leaf dry matter content.Secondly,removal of dominant sedge species and high-height grasses species pronouncedly decreased the standing biomass,but did not significantly impact on plant species diversity;contrastingly,plant diversity pronouncedly decreased but standing biomass did not remarkably decrease in response to removal forb species.The standing biomass positively correlated with remaining species diversity in later years of removal but not in the early three years of plant species removal.Thirdly,the temporal stability of standing biomass trend to decline with removal of more species,especially in removal of many moderate-height forb species,resulted from the fact that species removal not only decrease mean biomass but also increase the variation of biomass over years.Plots with more remaining species tends to have higher temporal stability due to higher diversity in conjunction with higher mean of biomass while lower variance of the biomass over years.Additionally,the temporal stability of the biomass also associated with species evenness and asynchrony.Finally,Plant species removal not only significantly decreased soil organic matter in all treatment but also tend to decrease soil nutrients,especially decrease soil P in response to removal of forb and grass species.the Bayesian network revealed that the loss of species diversity rather than standing biomass was directly associated with the decline in the soil quality,especially a decrease in soil available P.Taking together,we conduced following two novel insights.Firstly,the increase of ITV supports the importance of niche differentiation in maintaining plant diversity in this alpine meadow.However,the increase of ITV following species removal indicates that increasing ITV can partly buffer decrease of plant diversity induced by species loss,suggesting functional significance of plant plastic response and adaption in maintaining trait diversity and ecosystem functioning,which was been underestimated in previous experiment of biodiversity-ecosystem functioning.Secondly,our results show either species diversity nor temporal stability of standing biomass pronouncedly decrease following removal of grass or sedge species,but removal of common forb species not only significantly decrease the biomass stability but also pronouncedly decrease soil quality,especially a decrease in soil available P,which results from irreplaceable niche of forb species.Based on these results,we discussed the functional significance of plant plastic response and adaption in maintaining trait diversity and ecosystem functioning in response of plant meadows to climate change and grazing.Moreover,we highlighted the importance of forb plant in maintaining sustainability of ecosystem services on the rangeland of Tibetan Plateau.