Evolution Of Biogeochemical Niche Of Forest Plants At Different Successional Stages In The Mao’er Mountain Of Guangxi

In this paper,we collected leaves of dominant and common species from three different successional forests in the Cat’er Mountain Nature Reserve in Guangxi,and measured the contents of carbon(C),nitrogen(N),phosphorus(P),potassium(K),calcium(Ca),and magnesium(Mg)in leaves and soils during the peak growing season in July 2022.The leaf and soil elements were analyzed by phylogenetic conservatism and ecological stoichiometry,aiming to understand the evolutionary mechanisms of forests at different successional stages from the perspective of plant biogeochemical niches.The main results of the study are as follows:(1)There are differences in the systematic signals and evolutionary rates of element contents in leaves of forest plants at different successional stages,and the optimal evolutionary models are all Ornstein-Uhlenbeck(OU)models.No significant systematic phylogenetic signal was detected in the six elements of needle and broad-leaved mixed forest plants;Significant systematic phylogenetic signals were found in the five elements(C,N,P,K,Ca)of evergreen and deciduous broad-leaved mixed forest plants,and in the four elements(C,N,P,Mg)of evergreen broad-leaved forest plants.The results indicate that the six elements of needle and broad-leaved mixed forest plants are less affected by historical factors and more responsive to environmental changes.In contrast,the five elements(C,N,P,K,Ca)of evergreen and deciduous broad-leaved mixed forest plants and the four elements(C,N,P,Mg)of evergreen broad-leaved forest plants show the opposite pattern.(2)There were significant differences in the soil nutrient contents and the synergistic effect of plant leaf nutrients at different successional stages of forests,which jointly influenced the leaf element content of forest plants.For leaf C element,it was significantly higher in needle and broad-leaved mixed forest than in evergreen and deciduous broad-leaved mixed forest and evergreen broad-leaved forest(P <0.05);For leaf N element,it was significantly higher in evergreen and deciduous broad-leaved mixed forest than in evergreen broad-leaved forest and needle and broad-leaved mixed forest(P < 0.05);For leaf P element,it was significantly higher in evergreen and deciduous broad-leaved mixed forest than in evergreen broad-leaved forest,and significantly higher in evergreen broad-leaved forest than in needle and broad-leaved mixed forest(P < 0.05);For leaf K element,it was significantly higher in evergreen broad-leaved forest and evergreen and deciduous broad-leaved mixed forest than in needle and broad-leaved mixed forest(P < 0.05),and the same pattern was observed for leaf Ca element;For leaf Mg element,it was significantly higher in evergreen broad-leaved forest than in evergreen and deciduous broad-leaved mixed forest and needle and broad-leaved mixed forest(P <0.05).(3)Principal component analysis showed that principal component 1 explained50.1% of the variance and principal component 2 explained 15.8% of the variance.Leaf C,N,K,and Mg contents constituted principal component 1,while leaf P and Ca contents constituted principal component 2.Only the score of principal component 1 showed a significant difference,with evergreen and deciduous broad-leaved mixed forest and evergreen broad-leaved forest having significantly higher scores than needle and broad-leaved mixed forest(P < 0.05).This indicates that the differentiation of biogeochemical niches is mainly driven by the leaf element contents of C,N,K,and Mg.(4)Finally,the phylogenetic relationships of forest plants at different successional stages were further analyzed for their conservatism and plasticity in biogeochemical niches.The results showed that with the progression of succession,evergreen and deciduous broad-leaved mixed forest and evergreen broad-leaved forest had stronger conservative biogeochemical niches.In addition,the degree of biogeochemical niche separation for species in different habitats also varied,and some species had more "flexible" biogeochemical niches.