Effects Of Functional Diversity And Functional Redundancy On The Stability Of Alpine Meadow Community

The potential effects of biodiversity loss on ecosystem functioning and services is a hot issue which has been concerned by ecologists persistently. Species diversity (SD) includes both functional diversity (FD) and functional redundancy (FR), which represent dissimilarity and similarity of traits among species, affecting ecosystem functioning by mechanisms of ecological complementary and insurance effect. So a decline in species diversity or species loss, which caused the loss of plant functional traits, the changes in the composition of functional traits, or the reducing dimensions of traits space, will inevitably lead to the changes in functional diversity and functional redundancy, thereby affect the stability of community. The researches indicate that species diversity (SD) has positive effect on the stability of community. As the two important components of species diversity, The researches indicate that species diversity (SD) has positive effect on the stability of community. However, as the two important components of species diversity, how differences of the strength and relative importance of effects of the two components on community stability remains poorly understood. In this study, a field manipulation experiment was conducted in an alpine Kobresia humilis meadow at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2012, with the aim of gaining insight into the relationship between community stability, functional diversity, and functional redundancy. The experiment used a split-plot design with three clipping levels (stubbled 1 cm,3 cm, and unclipped) used on the whole plot, and subplots were treated with or without fertilizer (12.75 g·m-2·a-1 urea +3.06 g·m-2·a-1 ammonium phosphate or unfertilized). Our main results as follows:(1) Clipping treatment increased consistently species diversity, functional diversity and community stability, whereas fertilizing treatment has an opposite effect. Clipping and fertilizing treatments have no significant effect on functional redundancy (p>0.05), and the interaction between clipping and fertilizing treatment have no significant effect on species diversity, functional diversity, community stability and functional redundancy (p>0.05).(2) Functional diversity and community stability kept synchronous changes among clipping treatments and among fertilizing treatments, and functional redundancy maintained relatively constant. At the same time, the average coefficient of variation of functional diversity and functional redundancy was respectively 9.10% and 2.26%. So functional diversity is more variable than the functional redundancy under the disturbance condition.(3) The degree of positive correlation between functional diversity and species diversity was stronger than that between functional redundancy and species diversity, i.e. changes in species diversity that induced by experimental treatment led to a more trait divergence relative to trait convergence among species. Therefore, maintaining community stability resulting from species diversity mainly depended on stronger functional complementary, while insurance effect had less influence on stability.(4) Association of community stability with functional diversity is also stronger than that with functional redundancy. Therefore, even though the insurance effect of functional redundancy can also promote the stability of community, but the role of the complementary effect of functional diversity is better. Under the treatments conditions of this study, complementary effect caused by differences in functional traits among species is just the main driving force to maintain the stability of alpine meadow community.(5) Correlations between the community stability and the functional diversity were different with vary traits that used to calculate functional diversity. There are total 13 traits in here, only functional diversity calculated by three traits, i.e. specific leaf area (FDsia), leaf dry weight (FDldw) and growth form (FDgf), had greater contribution to the stability of the community. If we want to predict the changes of ecosystem functioning precisely by means of functional diversity, it is crucial to make choice of optimal trait(s) for eliminating the co-linearity and/or blackout effect result from redundant traits.(6) The treatments for the functional diversity of different characters to effect showed that the functional diversity calculated by plant height (FDh), above ground weight (FDagw),leaf dry weight (FDldw), growth form (FDgf), life cycle (FDlc) had bigger response to clipping, the functional diversity calculated by plant height (FDh), above ground weight (FDagw), leaf area (FDa), photosynthetic pathway (FDpp), organ of vegetative propagation (FDovp) had bigger response to fertilizer treatments.(7) The functional diversity calculated by the life cycle (FDlc) and functional diversity calculated by other traits has significant negative correlation, as the same time, it has significant negative correlation with functional diversity calculated by multiple traits (FD). The rest of the functional diversity index was significantly positive correlation between them, show the same change trend, namely the differences exist between these traits of degeneration. Although the average calculation characteristics of interspecific character difference (FD) of functional diversity and community stability relationship has its rationality, but the function of the single trait diversity degree of influence on the stability of the community by stepwise regression analysis is necessary to eliminate redundant characters.As such, these results suggested that the relative strength of the effects of functional diversity and functional redundancy on community stability was positively correlated with the degree of variation in functional diversity and redundancy under the disturbance conditions, which confirmed our speculations. Meanwhile, functional diversity was more closely related to the community stability and could be a better predictor of ecosystem stability than species diversity or functional redundancy. Our study provides a critical insight into sustainable management of rangeland ecosystems.