| Plant functional traits could not only objectively reflect the response of vegetation to environmental changes,but also build a good connection of environments,individuals and the structures and functioning of the ecosystem,so it has been an important research method to understand the relationship between biodiversity and ecosystem functioning(BEF)and its response mechanism to environmental changes.In this paper,we firstly focused on the following 2 questions during successional stages of broad-leaved Korean pine(Pinus koraiensis)mixed forest along the latitude in Northeast China:(1)Changes of community functional traits and functional diversit ies for some key plant traits along latitude and during community succession,and their relationships with environments,to explore the response and adaptation strategies of vegetation to environmental gradients.(2)Effects of environmental gradients,community functional traits and functional diversities on forest biomass and productivity,changes of their relative importance with climate and community succession,to test several key hypotheses for explaining BEF relationships.Then,we used forest data across China to test whether our findings in Northeast China could be extended to a larger scale,and focused on:(3)Effects of functional traits and diversities on forest biomass,and changes of their relative importance with climate across China.(4)How to use the core functional trait(tree height)to shape the forest biomass across China.The main results are:(1)Changes of community functional traits and functional diversities and their relationships with environments:① With the increase of latitude in Northeast China,the community functional traits of specific leaf area,seed mass,wood density and leaf nitrogen content decreased but leaf phosphorus content increased,and these changes along latitude were significant.Among all traits,only the Rao’s quadratic diversity of specific leaf area significantly decreased.② During successional stages of broad-leaved Korean pine(Pinus koraiensis)mixed forest in Northeast China,the middle stage of succession is the key stage for a transformation of community functional traits,except that the CWM value of the maximum tree height was the lowest(it reached the top in the late stage),CWM values of other 5 plant traits all reached the bottom in the middle stage of succession.The Rao’s quadratic diversity values of the maximum tree height,specific leaf area and leaf nitrogen content significantly increased with the development of community succession,and the Rao’s quadratic diversity value of leaf phosphorus content showed a remarkable pattern that the middle was high and the sides were low(it reached the top in the mid-late stage).③ All community functional traits and diversities were mainly influenced by the independent effect of climate or biological factors,suggesting that climate plays a decisive role in shaping the large-scale pattern of vegetation functional traits,and species presenting characteristics enable species to pass through environmental filters and establish in a given location,resulting from the associations and interactions between species.(2)Effects of biodiversity on ecosystem functioning along the latitudinal and successional gradients in Northeast China:① In addition to environments,"sampling effect" and"complementary effect" still revealed significant effects,in which "sampling effect" was dominant.②With more favorable climate,the independent effects of "sampling effect" and "complementary effect" decreased in explaining productivity variation,while the total effects and their respective shared effects with environments increased;the independent effects of both increased in explaining biomass variation,while the total effects and their respective shared effects with environments decreased.③ During community succession of broad-leaved Korean pine(Pinus koraiensis)mixed forest in Northeast China,the "sampling effect" weakened and the "complementary effect"strengthened,supporting the hypothesis that there would be a transformation from sampling effect to complementary effect over time.④ Relationships between different plant functional traits and environments,and their effects on ecosystem functioning were different,but they seemed to follow this pattern:functional diversity could be positively related with biomass and productivity;trait values that intensify resource conservation could be positively related with biomass but be negatively related with productivity,whereas trait values that intensify resource acquisition could be positively related with productivity.(3)Effects of biodiversity on forest ecosystem functioning across China:① Most of the’effects’ of richness and functional group identity(FGI)on forest biomass were shared with environments,but richness and FGI still revealed significant effects in addition to environments,suggesting that richness and FGI do have significant effects on ecosystem functioning but their effects change with environments.② Richness and FGI explained biomass mainly through their shared effects instead of independent effects,suggesting that the positive biodiversity effect is closely associated with a sampling effect ③ The relative effects of richness,FGI and environments varied latitudinally from boreal to subtropical forests;a)the independent effects of environments and richness decreased,whereas the total effect of FGI increased;b)the slope of richness-biomass relationship decreased monotonically,possibly because of decreasing complementarity and increasing competition with increasing productivity.Our results suggest that while species richness does have significant effects on forest biomass it is less important than environmental gradients and other biotic factors in shaping large-scale biomass patterns.(4)In predicting forest biomass across China with core functional trait(tree height),we found:forest height alone explained 62%of variation in forest biomass across China,but the relationship between biomass and forest height were signifcantly affected by climate,forest biome,leaf phenology and leaf form.Among which,the effect of climate was stronger than other factors.When the effects of climate and biotic factors were considered in the models,geographic biomass patterns could be well predicted from forest height with an r2 between 0.63 and 0.78.We provided the broad scale models to estimate biomass from forest height across China,which can be utilized by future LiDAR studies.In this study,we studied the patterns of plant functional traits and diversities and their effects on ecosystem functioning along climatic and successional gradients respectively,our results suggest that the climatic and successional gradients could not only directly affect the distribution of plant functional traits and biodiversity,also affect their effects on ecosystem functioning.While these patterns and effects varied regularly along environmental gradients.Although the response strategies of different plant functional traits to environmental gradients and their effects on ecosystem functioning are different,they follow a certain pattern.Understanding these patterns not only helps to understand the response of vegetation to global climate change,but also helps to understand the real effect of biodiversity in nature.At the same time,it would be a very important theoretical guiding for the management,ecological restoration,biodiversity protection and carbon sink monitoring of a large number of forests in China. |
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