| Plant functional traits can indicate the response of plants to environmental change and affect ecosystem functioning.Community functional composition is the trait composition at community level,which provides a unique insight into the response of plants to global change at the community scale.Global change factors can shift community functional composition by driving changes in community species composition(including species abundance and species occurrence)and intraspecific trait variability(phenotypic responses of individual plants and genotypic differentiation),thus affecting ecosystem functioning(e.g.,aboveground biomass).However,the role of intraspecific trait variability was often ignored in previous studies.More specifically,the relative importance of intraspecific trait variability and species composition change in determining community functional response to global change,especially under the interaction of multiple global change factors,remains still unclear.The Tibetan Plateau represents one of the biodiversity hot areas.Alpine meadow,one of the typical grassland types on the Tibetan Plateau,plays an important role in providing ecological service and functioning.As the "Third Pole" of the world,the Tibetan Plateau with a high average altitude is fragile and sensitive to climate change.It is undergoing global change caused by human activities,including nitrogen deposition,elevated temperature and altered precipitation,which may exert tremendous impacts on plant community and ecosystem functioning in the alpine meadow.We conducted a three-way factorial field experiment,including nitrogen addition,warming and altered precipitation,to examined the effects of global change on community functional composition by measuring seven plant functional traits(plant height,leaf area,SLA,LDMC,chlorophyll,LNC and LPC).Using the sum of squares decomposition,we quantified the relative contribution of intraspecific trait variability and species turnover in driving community functional response to global change.We explored the effects of community functional composition on ecosystem functioning by analyzing the relationship between aboveground biomass and functional composition.The main results of this study are as follows:1)Nitrogen addition and warming changed community functional composition while altered precipitation and interactions of global change factors had no significant effects.Compared with the control,nitrogen addition drove a shift in community function towards a more acquisitive resource-use strategy by increasing community-wide SLA,LNC,plant height and leaf area and decreasing LPC.Warming caused a shift of plants towards a more conservative strategy through decreasing SLA,LNC and LPC and increasing LDMC and plant height at the community level.2)The relative importance of species composition change and intraspecific trait variability in driving changes in community functional composition was different under nitrogen addition and warming.The nitrogen-induced functional shifts(changes in plant height,LA,SLA,LNC and LPC)were mainly explained by intraspecific trait variability,and the relative contribution of intraspecific variability(33.44%,8.57%,59.02%,89.21%,53.03%,respectively)was greater than that of species composition change(0.34%,1.75%,2.15%,0.5%,0.61%,respectively).Under warming,the relative contribution of species composition change(2.04%,4.11%;mainly species abundance)was greater than that of intraspecific variability(0.00%,0.71%)in determining the response of leaf morphological traits(SLA and LDMC),and the relative contribution of intraspecific variability(1.25%,1.77%,3.14%)was greater than that of species composition change(0.85%,0.00%,0.18%)in driving changes in plant height and leaf chemical traits(LNC and LPC).3)Community functional composition can predict aboveground biomass.Community mean height,leaf area,SLA,LNC and aboveground biomass were positively correlated.However,there was no significant correlation between aboveground biomass and LDMC,chlorophyll content and LPC.This study suggests that different global change factors would change community functional composition through distinct mechanisms in the alpine meadow.This finding provides theoretical support for better understanding and predicting the changes of plant community in the Tibetan alpine meadow under the scenario of global change in future. |
