Impacts Of Plant Functional Diversity On Leaf Litter Decomposition In Eastern Zhejiang Province

The relationship between biodiversity and ecosystem function is one of the hot issues in ecology over the past three decades.Currently,most studies focus on the relationship between plant diversity and ecosystem productivity,but with less attention on another important ecosystem functionality relevant to the biogeochemical processes.Litter decomposition is an important ecosystem process linking with material cycle and energy flow,thereby affects the composition of soil organic matter and the mineralization of nutrients in terrestrial ecosystems.Exploring the relationship between plant functional diversity and litter decomposition is crucial for a deeper understanding how plants with distinct functional strategies drive ecosystem function.In this study,eight tree species were selected from different locations on the plant economics spectrum,including Sapindus saponaria,Koelreuteria bipinnata,Liquidambar formosana,Sapium pleiocarpum,Neolitsea sericea,Machilus thunbergii and Schima Superba,Cyclobalanopsis glauca,to experimentally simulate a range of plant functional diversity by using the controlled high-density plantation.Species were ranked according to the variations in leaf longevity,leaf dry matter content,specific leaf area,leaf nitrogen content,mean leaf area and stem wood density.Then plant species were divided into four different spectral segments along the fast-slow growth spectrum(PC1 in trait axis)to set up different functional diversity treatments.Ten of the functional diversity treatments were selected in this study.I chosen leaf litter of Liquidambar formosana,Machilus thunbergii and Cyclobalanopsis glauca litter to conduct the decomposition experiment along a gradient of plant functional diversity.The periodic and cumulative litter mass loss rates and small-and medium-sized invertebrates in the litter bags were tracked across five decomposition stages over a one year.The main results detailed below:(1)With the increase of tree functional difference(i.e.,the Rao quadratic entropy),the cumulative weight loss rate of the three species litters increased significantly.However,there was no significant change of the litter weight loss rate with increase of tree functional composition(i.e.,the community-weighted mean values of tree traits).These results indicate that the effects of tree functional difference is more important than the effects of functional composition to drive variation in litter decomposition rate.(2)At the initial stage of decomposition,there was a significant positive relationship between litter decomposition rate and tree functional diversity for three species.However,with the decomposition proceeding,the positive effect of functional diversity on the litter decomposition weakened for Liquidambar formosana and Machilus thunbergii gradually,but amplified for Cyclobalanopsis glauca.These results indicate that the tree functional diversity mediated niche complementarity effects on litter decomposition depend not only on the time,but also species’ growth strategyspecific.(3)Acari and Collembola were the dominant species harvested from litter bags.At the initial stage of decomposition,individual abundance and group number of soil fauna in litter bags were significantly higher in Liquidambar formosana than in Machilus thunbergii and Cyclobalanopsis glauca.With the decomposition preceeding,these differences gradually disappeared.In addition,there were significant positive relationships between litter mass loss rate and individual abundance of soil fauna for Liquidambar formosana and Machilus thunbergii.These results indicate that the soil fauna mainly influence leaf litter decomposition at the early decomposition stage,and act strongly on the luxurious species.(4)There was no significant positive relationship between tree species diversity and soil fauna diversity,but tree functional diversity significantly affected soil fauna diversity.These results suggest that the differences in soil fauna involving in litter decomposition are mainly determined by tree functional diversity,instead of the number of tree species.(5)The structural equation model showed that the cumulative litter mass loss was affected by tree functional diversity and litter substrate difference.Comparably,the periodic litter mass loss was interactively influenced by the direct positive effects of tree functional diversity and the indirect negative effects of litter substrate difference via soil fauna abundance.These results imply that fauna diversity mediates leaf litter decomposition mainly through litter substrate decomposition,regardless of tree functional diversity.In conclusion,based on a plant functional diversity control experiment,this thesis studied on the relative contribution of tree functional diversity,soil fauna diversity and litter substrate difference on leaf litter decomposition rates over three functionally dissimilar woody plant species.The results demonstrate that,as compared to species diversity,the tree functional diversity-mediated niche complementarity effects benefit not only to soil fauna abundance,but also interactively facilitating litter decomposition.This findings are helpful for better understanding the mechanism of how plant diversity impacts ecosystem function with respect to the matter cycling.