The Patterns And Driving Mechanisms Of Community Phylogenetic And Functional Structures Over Forest Succession In Linggu Temple,Nanjing Province

Community succession is the key issue of ecological research and the theoretical basis for ecological restoration.In recent years,with the development of phylogenetic and functional traits-based community ecology,revealing how phylogenetic and functional traits structures vary with succession is an increasingly important area of community ecology.Some studies found that community phylogenetic structure and functional traits structure tended to overdispersion or clustering over long-term succession.In addition,it has also been found that there are opposite or inconsistent trends in the structure of phylogenetic and functional traits that may reflect the diversity of relative importance among ecological processes(competitive exclusion and environmental filtering,etc.).It is worth noting that the same ecological process,such as competitive exclusion,may lead to clustering or overdispersion of community structure,so the ecological process and community structure cannot correspond one by one.However,there is no unified conclusion so far.On the one hand,this may be due to the lack of long-term data on successional dynamics,most studies focus on shortterm communities.On the other hand,there is lacking the studies exploring the impact of species composition on community dynamics from the species colonization and extinction perspective.In this study,based on four surveys data in the Nanjing Linggu Temple Forest transects through 68 years,we explored the trend of community phylogenetic and functional traits structures of Linggu Temple forest,and further combined species colonization and extinction to explore the forest community assembly mechanism in Linggu Temple Forest.The results are as follows:(1)Over long-term succession of Linggu Temple Forest,the phylogenetic structure shifted from clustering to overdispersion,while the functional traits structure shifted from overdispersion to clustering.The phylogenetic structure is clustered in early community succession,which may imply that environmental filtering plays a dominant role during this period.Meanwhile,strong competitive exclusion among species with similar traits leaded to clustering of functional traits structure.In the later period of community succession,the phylogenetic structure tends to be overdispersion,which may be caused by the enhanced habitat heterogeneity.Meanwhile,the more clustering of functional traits may be due to the effect of environmental filtering.Consistent results were drawn based on different null models.Besides,we also explored the phylogenetic and functional traits structures change in the masson pine forest and broad-leaf forest communities respectively,and the results showed that the phylogenetic structure of the masson pine forest shifted from overdispersion to random over succession,and finally be overdispersion.However,the phylogenetic structure of broad-leaf forest shifted from random to clustering over succession,and finally be random.These may be due to the difference in the initial stand structure,which would lead to different relative importance of environmental filtering with competitive exclusion on the community structure of masson pine and broad-leaf forests in different succession periods.Furthermore,we found that functional traits in both masson pine forests and broadleaf forests tended to more cluster over succession,possibly driven by enhanced effects of environmental filtering.(2)By calculating the phylogenetic and functional traits distances between colonized/extinct species and resident species,as well as the within colonized/extinct species,we explored the relative contributions of species colonization and extinction at different successional stages to changes of community structure.The results show that in the early stage of Linggu Temple forest succession,the extinct species,which have closer phylogenetic relatedness than the resident species and have more dissimilar traits within them,drove the overdispersion of phylogenetic structure and the clustering of functional traits structure.In the later stage of succession,the colonized species,which have more distantly phylogenetic relatedness than the resident species and have more similar traits within them,and the extinct species which have more dissimilar traits within them,drove the overdispersion of phylogenetic structure and the clustering of functional traits.In addition,the impacts of species colonization and extinction on community structure were also found in masson pine forests and broadleaf forests.Especially in the later stage of succession,colonized species were more distantly related than the resident species in masson pine forest communities,driving the overdispersion of phylogenetic structure.For the broad-leaf forest community,at the later stage of succession,the extinct species were more closely related than the resident species,which driving the phylogenetic structure from clustering to random.For the change of functional traits,we found that the extinction of species with dissimilar traits may be the main driver for the clustering of functional traits structures in masson pine and broad-leaf forests,especially in the later stages of succession.In summary,this study found that the phylogenetic structure of the Linggu forest community became overdispersion over the succession,while the functional traits structure tended to be clustering.The results suggest that the extinction of closely related species with different functional traits caused by competitive exclusion may play a more important role in early succession.Over succession,the improvement of environmental quality and the effect of environmental filtering lead to the colonization of distantly related species with similar functional traits,which driving community structures tended to be phylogenetic overdispersion and functional clustering.Linggu Temple forest has already completely transitioned from a mixed coniferous and broadleaved forest to a deciduous evergreen broad-leaved mixed forest.In the next two decades,the main driving force may be the extinction of species with similar functional traits and phylogeny,driving the overdispersion of the community structure.In the future,predicting changes in community dynamics may be more important by focusing on species extinctions.Therefore,our results provide the useful guidance for ecological restoration.In the early stage of succession,we should focus on the species extinction;in the later stage of succession,we should pay more attention to the phylogenetic and functional difference between colonized species and resident species.