Effects Of Conspecific Leaf Litter On Offspring Regeneration Of Dominant Species In Tiantong,zhejiang

Community regeneration is a key process for maintaining the coexistence of community species.Exploring the influencing factors on community regeneration can better explain the mechanism of community species coexistence.Litter layer is the first environmental medium for seed after their falling.Meanwhile,litter is a important factor affecting seed germination and seedling regeneration.Especially the conspecific leaf litter as the main component of litter layer around focal tree,can affects seed germination and seedling regeneration through physical,chemical and biological way respectively.But few experimental studies focals on the mechanism of conspecific leaf litter influencing offspring regeneration.Therefore,this study selected five dominant species in subtropical evergreen broad-leaved forest in Tiantong,Zhejiang province as the research objects.We set up five different treatments in the greenhouse(none sterilized soil;sterilized soil;none sterilized conspecific leaf litter+ sterilized soil;sterilized conspecific leaf Litter+ sterilized soil;leaching solution + sterilized soil)and monitored seed germination and seedling growth.Then we designed the Generalized Linear Mixed Models and Linear Mixed Models to analyze the effect of the conspecific leaf litter on seed germination and seedling growth,and compare with the soil effect.This study aim to reveal the effect mechanism and temporal differentiation characteristics of the conspecific leaf litter on offspring regeneration.The main research results are as followings:At the seed germination stage,leaf litter of Daphniphyllum oldhami and Neolitsea aurata var.chekiangensis hampered the conspecific seed germination by forming physical barrier;in addition,Daphniphyllum oldhami leaf litter also inhibited seed germination by mediating host-specific phyllospheric pathogenic microorganisms.However,the soil mycorrhizal fungi surrounding the adult trees of Daphniphyllum oldhami and Cyclobalanopsis sessilifolia promoted the conspecific seed germination by breaking seed dormancy and efficiently transferring nutrients from the soil to the seeds.At the seedling stage,the steriled leaf litter of Daphniphyllum oldhami and Machilus thunbergii could release necessary nutrients for the conspecific seedling growth during the rapid decomposition process.At the same time,it would also release a large number of secondary chemicals to help seedlings resist pests and diseases,then promoted the seedling survival.On the contrary,the secondary chemicals from Neolitsea aurata var.chekiangensis decaying leaf litter inhibited the conspecific seedling growth and showed obvious autotoxicity effect.In addition,the Cyclobalanopsis sessilifolia leaf litter was hard and had a high lignin content,which led to a slower decomposition rate.Therefore,a large amount of Cyclobalanopsis sessilifolia leaf litter covering the soil surface would affect the soil breathability,reduce the seedling roots respiration,and thus inhibit seedling survival.The Daphniphyllum oldhami leaf litter mediated host-specific phyllospheric pathogenic microorganisms and inhibited the conspecific seedling survival.Compared with the multi-pathway effects of conspecific leaf litter,the ectomycorrhizal fungi in the soil surrounding the adult trees of Daphniphyllum oldhami,Neolitsea aurata var.chekiangensis and Machilus thunbergii promoted the seedlings growth because of their defense against the invasion of the protobacteria.Synthesis: Compared with the soil,the conspecific leaf litter effects on seed germination and seedling growth stage,not only had diversity,but also could reflect certain temporal differentiation characteristics.At the seed germination stage,Daphniphyllum oldhami leaf litter mainly inhibited the conspecific seed germination by mediating phyllospheric pathogens,but in the late seedling growth stage,leaf litter mainly release nutrients through rapid decomposition to promote seedling growth.However,at the Neolitsea aurata var.chekiangensis seed germination stage,the seed germination was mainly inhibited by physical covering of the conspecific leaf litter,but when the seed germinated and formed a seedling,it was higher than the leaf litter layer,and the conspecific leaf litter released secondary chemicals,which inhibited the seedling growth by autotoxicity.Clarifying the diversity and temporal differentiation characteristics of conspecific leaf litter on offspring regeneration can explain the importance of conspecific leaf litter in community regeneration on mechanistic level.