The Relationship Between Species Diversity, Functional Diversity And Time Stability Of Alpine Meadow Communities

Since the loss of biodiversity affects the ability of ecosystems to provide reliable products and services to humans,the relationship between biodiversity and ecosystem stability is a long-standing issue in ecology.Although their relationship is still in dispute,most current studies support the diversity-stability hypothes is proposed by Mac Arthur(1955).Most of the previous studies on this relationship have been carried at the level of species diversity(SD)or functional group diversity(FGD).However,many scholars believe that research should not be limited to only one component of biodiversity(such as species diversity).It is necessary to comprehensively consider the effect of diversity on the ecosystem stability at different levels of biological organizations and at different levels of the same hierarchy.As an important component of biodiversity,functional diversity(FD)has received increasing attention in recent years and is considered to have a more immediate effect on ecosystem functions.However,there were few studies on the relationship between functional diversity and community temporal stability.The introduction of functional diversity to the study of diversity-stability relationships can expand researches in this field because it helps to more comprehensively illustrate the relationship between diversity and ecosystem functions and distinguishes the differences between species diversity based on species and functional diversity based on functional traits.This study was conducted in the natural grassland communities of alpine meadows with clipping(stubbled lcm(HC),3cm(MC)and non-clipping(NC))and fertilization(fertilization and non-fertilization)treatments from 2007 to 2017.The species abundance data were obtained through a community survey and five quantitative traits(plant height,individual aboveground weight,chlorophyll content,leaf area,and specific leaf area)of the plant were measured to calculate three species diversity indices(i.e.species richness(SR),Simpson index(D)and Shannon-Wiener index(H'))and three functional diversity indices(i.e.functional richness(FRic),functional evenness(FEve)and functional dispersion(FDis))and community temporal stability index.We studied the changes of species diversity,functional diversity and temporal stability of communities,the relationship between species diversity and temporal stability of communities and relationship between functional diversity and temporal stability of communities and the temporal stability mechanisms in the communities under disturbance of clipping and fertilization.The results show as follows:(1)Clipping had a positive effect on SR and H' and had no significant impact on D.The clipping treatment without fertilization significantly increased D,but the clipping with fertilization had no significant effect on D.Fertilization resulted in a significant reduction in SR,D and H'.Clipping and fertilization had opposite effects on species diversity and fertilization had a greater impact.SR,D and H' declined with the year,especially in the long-term fertilization communities.As a result,the difference of species diversity in these two communities increased.(2)Clipping significantly increased FRic and FEve and significantly reduced FDis.Fertilization significantly reduced FRic,FEve and FDis.FRic and FDis showed fluctuations between years in the non-fertilization communities,but decreased with time in the fertilization communities and the difference between fertilization and non-fertilization communities increased.FEve had no significant difference among years.Clipping and fertilization had the opposite effects on FRic and FEve,but had consistent negative effects on FDis.The effect of fertilization on functional diversity was greater than that of clipping.(3)Clipping had no significant effect on the temporal stability of communities,while fertilization significantly reduced the temporal stability of communities.This was directly related to the decrease of species diversity and functional diversity in fertilization communities,further confirming some studies on the prediction that nutrient enrichment may lead to community instability.In this study,the species diversity and functional diversity were positively correlated with temporal stability of communities in compound communities of clipping and fertilization treatments.The optimal models were all exponential functions.Therefore,studies on two aspects of biodiversity(species diversity and functional diversity)support the diversity-stability hypothesis.The optimal model was different from the saturated growth model predicted by the existing theoretical research,indicating that the species diversity and functional diversity of community of the study may not reach saturation.(4)Because the species diversity indices D and H' were more closely related to temporal stability of communities and the types of relationships of these two species diversity indices and the temporal stability of communities were the same in communities with same treatments.Thus,D and H' could better explain the changes of the temporal stability of communities.In functional diversity indices,FDis was most closely related to temporal stability of communities,and was the most effective functional diversity index to predict the changes of the temporal stability of communities.Therefore,in terms of functional diversity,the maintenance of temporal stability depends to a greater extent on the average distance between species in the functional trait space or the ability to buffer environmental changes resulting from differences in species traits.That's to say,the niche complementarity effect increases the temporal stability of the alpine meadow community under disturbance of clipping and fertilization.(5)Our study shows that the relationship of species diversity-temporal stability and functional diversity-temporal stability was dependent on disturbance.For the same species diversity index,the relationship between it and temporal stability of communities tends to vary with the level of clipping intensity or whether it was fertilized.Therefore,the saturation-increased relationships shown by the research conducted in a stable environment or conducted by theoretical predictions may overlook the potential impact of complex and variable environments in natural communities.The dependence of the relationships between functional diversity and temporal stability of communities on the environment was embodied in differences of the disturbance factors(mowing and fertilization)and differences of clipping intensity,but mainly depended on the differences of the levels of soil nutrients.(6)Our study indicates that there was asynchrony of species fluctuation in each community because the species synchronism values(?b)of all communities were all not more than 1.Clipping had no significant effect on ?b,while fertilization significantly increased it.Therefore,the degree of species asynchrony fluctuation in the different mowing treatment communities was same,but the asynchrony of fertilization communities was lower than that of non-fertilization communities.This was compliance with the impacts of clipping and fertilization on temporal stability of communities.Therefore,in each community of clipping treatment,the changes of species diversity and ?b caused by changes in soil nutrients leads to a significant negative correlation of them,that was,fertilization reduced diversity and also led to a decrease in asynchrony effect,which in turn reduced temporal stability of communities.The main driving force to change the asynchrony of alpine meadow species was the change of soil nutrients.Although mowing can increase species diversity,it had no effect on the temporal stability and ?b,so it had less effect on the asynchronous stabilization.Among three species diversity indices,D and H' were more effective indicators to predict the asynchrony change of species in the community.From the perspective of the relationship between functional diversity and species synchrony,the role of the changes of soil nutrient in driving asynchrony was also proved.Among three functional diversity indices,FDis was the most effective indicator to predict the asynchrony change of species in a community.This was consistent with the result that FDis was the most effective functional diversity index to predict temporal stability of communities.(7)There were portfolio effects in all treatment communities in our study and increased with the level of clipping.At the same time,the portfolio effect was also driven by the soil nutrient status.Another reason why fertilization reduced community temporal stability was that it reduced the species diversity,which in turn reduced the stabilization effect of portfolio effects.Compared with fertilization communities,portfolio effects were stronger in non-fertilization communities.Because of the lack of expected correlation between functional diversity and summed variance in most treatment compound communities in this study,it may indicate that functional richness,functional evenness,and functional dispersion were not effective predictors of changes in species summed variance.In other words,the strength of the community portfolio effect cannot be explained by the changes in functional diversity.In conclusion,mowing and fertilizing have different effects on species diversity,functional diversity and temporal stability of communities and their relationships.The positive effects of clipping on diversity and community stability cannot offset the negative effects of fertilization,mainly because fertilization reduced the species diversity and functional diversity of community and also reduced the asynchrony effects and portfolio effects.These two mechanisms were conductive to the stability of the communities.In our study,the relationships of species diversity-temporal stability and the relationships of functional diversity-temporal stability of the communities depend on the disturbance factors or disturbance intensity.At the same time,among the six diversity indices used in this study,Simpson index(D),Shannon-Wiener index(H')and functional dispersion index(FDis)were the most effective indicators to predict the variations of temporal stability of communities.These results were important supplements to previous theoretical researches.Therefore,when we study the diversity-stability relationship,we must fully consider the impact of external interference and focus on the choice of diversity indices so that the relationship between diversity and ecosystem function could be more comprehensive understanding.