The Effects Of Mowing And Fertilization On The Relationship Between Species Diversity, Functional Diversity And Ecosystem Versatility In Alpine Meadows

Classical researches on the relationship of biodiversity and ecosystem function(BEF)showed that biodiversity could improve and stabilize ecosystem functions,but ignored the valuable feature that ecosystem can maintain multiple ecosystem functions simultaneously,namely ecosystem multifunctionality(EMF).Previous studies focused on ecosystem single functions have underestimated the effects of biodiversity.Recently,the studies of the relationships between biodiversity and ecosystem multifunctionality(BEMF)has gradually become one of the hotspots in ecology,and the important role of species diversity in EMF has been emphasized.However,compared with BEF researches,there are still many problems to be explored in the rapid developing of BEMF researches.For example,BEF studies have shown that functional diversity,as an important component of biodiversity,is more directly related to ecosystem functions.However,little is known about its relationship with EMF and the mechanisms of its effect.Compared with species diversity,it's unknown whether functional diversity has more direct relationship with EMF.In order to understand the relationships and mechanisms between biodiversity and ecosystem multifucntionality in alpine meadow ecosystem more comprehensively,a research based on a field simulation experiment of livestock grazing and nitrogen deposition control in alpine meadow of the Qinghai-Tibet Plateau was conducted to study the relationships of species diversity,functional diversity and EMF.In this study,the single function of ecosystem,i.e.aboveground net primary production(ANPP),temporal stability of community(Scom)and function of soil nutrient cycling(SNC)was estimated by using the data of community aboveground biomass and soil nutrient content measured from 2012 to 2017.Based on the number of species in the community,the relative abundance of species and the some key plant functional traits[such as plant height(H),aboveground weight per plant(AGW),leaf area(LA)and specific leaf area(SLA)],we calculated the species diversity[including species richness(SR),species evenness(SE)and Simpson's diversity index(D)]and the functional diversity[including functional richness(FRic),functional evenness(FEve),functional dispersion(FDis)and community weighted mean per trait(CWM)].According to the estimated single function of ecosystem,we employed the averaging approach and the single function approach to quantify the ecosystem multifunctionality.Some statistical methods,such as Univariate ANOVA,curve regression and structural equation modeling(SEM)were used to study related questions.The results are as follows:(1)Since EMF increased significantly after clipping and fertilizing,but was not significantly affected by their interaction,these two disturbance factors should independently improve the ability of ecosystem to maintain multiple functions.(2)The relationship between diversity and ecosystem function was strongly dependent on disturbance factors and the single ecosystem function considered,which was not as positive as many previous studies.Our study showed that the increase of ANPP and SNC was mainly determined by the increase of CWM.This is in line with the prediction of the mass ratio hypothesis.The increase of Scom depended entirely on the increase of species diversity and multidimensional multiple traits functional diversity,which is in line with the prediction of diversity hypothesis.The relationship between diversity and ecosystem multifunctionality was also dependent on disturbance and diversity components,and the proportion of positive correlation was still low.The increase of EMF mainly depends on CWM rather than species diversity or polyVictoria functional diversity.(3)The results of simple linear regression and stepwise linear regression showed that the best predictor of CG community all was functional dispersion(FDis)and the other communities all were CWM,and the former indicated CWMH was the best predictor of MC community,the latter was SE.The above results suggested that the best predictors of EMF in different treatment communities are different,and the selected indicators were closely related to EMF.(4)SEM analysis showed that among the potential disturbance and diversity factors(including clippng fertilizing,species diversity,multidimensional multiple trait functional diversity and community weighted mean),clipping had no direct effect on EMF(path coefficient=0.082),but fertilizer had a direct positive effect on it(path coefficient=0.905).At the same time,clipping and fertilizing can have positive and negative indirect effects on EMF through the community weighted mean(CWMLA)of leaf area,and CWMLA was the only diversity factor affecting EMF.(5)ANPP,Scom and SNC of the three single ecosystem functions significantly improved EMF,but the relative contribution of SNC was the largest(path coefficient=0.726),followed by ANPP(path coefficient=0.490),and the contribution of Scom was the lowest(path coefficient=0.362).This is consistent with the direct positive effect of fertilizer on EMF reflected in SEM analysis.In conclusions,clipping and fertilization can significantly enhance the ability of alpine meadow ecosystem to maintain net primary productivity,stability and soil nutrient cycling function at the same time.Species diversity and functional diversity both play important roles on EMF,similar to the results of BEF studies,but functional diversity is the best index to predict ecosystem multifunctionality in complex environments.The relationship between diversity and EMF was influenced by both the disturbance factor and the single ecosystem function used to measure the multifunctionality.Compared with biological factors,disturbance had a more direct and significant impact on EMF.Therefore,we should pay attention to the protection of species diversity in alpine meadow,and meanwhile reasonable grassland management measures should be taken to stabilize its multifunctionality.