Variation Of Plant Functional Characters In Tropical Cloud Forest

Due to the increasing uncertainty of global change,the impact of forest environment change on community construction is an urgent problem to be solved in forestry.Functional traits are the adaptive performance of plants in the process of growth,reproduction and survival that reflect the adaptive strategies of plants to the environment.How do the adaptive strategies of forest plants adjust to environmental changes and with the scale of a community organization? To answer this question,very little information was found in the literature and future research is needed to fill this research gap.Tropical cloud forest(TCF)has a unique community structure,environmental conditions and rich species diversity.The plant adaptation strategies to the environment may be different from other forests.In 2011,21(20×20 m)plots were constructed in Bawangling tropical cloud forest,Hainan Island.The species diversity of woody plants with DBH above 1cm in all plots was investigated.Plant functional traits,air temperature,humidity and soil nutrient contents were measured at individual and species levels.To observe variation in species diversity in TCF,we study the changes in plant functional traits along with environmental conditions.Moreover,we also explore the plant’s adaptation strategies in tropical cloud forests with environmental changes.The main results are as follows:(1)The species richness in the tropical cloud forest of Bawangling in two different years was shown with a sequence of Sapling > Adult tree > Large tree and the number of individuals was shown with a sequence of Sapling > Adult tree > Large tree.The Shannon-Wiener index of all plant species diversity increased in 2021 as compared to2011,while the highest change was found in different diameter classes in the young trees.The Simpson diversity index of all plant species was unchanged overall,but the highest change was found in different diameter classes in the large-size trees.The Pielous evenness index of all plants showed a decreasing trend,among them the highest change was found in different diameter classes in the mature trees.Furthermore,the number of species increased but the number of individuals decreased in 2021 as compared to 2011.The study on the supplementation,mortality and growth rate of plants in 2011 and 2021 showed that the supplementation and mortality rate of young trees and the growth rate of adult trees were found highest between two years.The addition,mortality and growth rate of large trees were the smallest,but the number of species and individuals increased.(2)The soil total nitrogen(TN)and available nitrogen(AN)in tropical cloud forests increased significantly in 2021 as compared to 2011 by using ANOVA analysis,while the soil organic matter(SOM),total phosphorus(TP)and available phosphorus(AP)decreased significantly.The Mann-Kendall test showed that the maximum air temperature showed an increasing trend,while the average air relative humidity and minimum air relative humidity showed a decreasing trend.Based on the principal component analysis(PCA),the environmental factors with maximum loading values were TN,TP,AN and minimum air relative humidity in 2011.Similarly,the environmental factors with maximum loading values were the soil OM,TP,maximum air temperature and minimum air relative humidity in 2021.The chlorophyll content and leaf thickness at the individual level increased significantly in 2021 as compared with 2011 by using a Wilcoxon test,while specific leaf area decreased significantly.At the species level,leaf thickness(LT),leaf chlorophyll(LC),stem total nitrogen(STN)and leaf total nitrogen(LTN)contents increased significantly in 2021 as compared with 2011,while stem soluble sugar content and leaf total phosphorus(LTP)contents decreased significantly.At the community level,LC,LT,STN,STP and LTN content increased significantly in 2021 as compared with 2011,while stem density,stem soluble sugar and leaf total phosphorus content decreased significantly.Multivariate regression analysis showed that soil nutrient content(such as soil OM,TP,AN content,etc.)and climate factors(maximum air temperature,minimum air relative humidity)jointly affected the changes of plant individual,species and community functional traits,and soil nutrient factors played a significant role.The intensification of soil P stress was the key factor affecting the functional traits of the community organization level.(3)Traits reflecting water use,rapid growth,photosynthesis,and environmental stress defense were combined and found by standard spindle regression(SMA)analysis.Six functional traits combinations of SLA-DBH(Specific leaf area,SLA;Diameter at breast height,DBH),SLA-LTh(Leaf thickness,LTh),SLA-WD(Wood density,WD),LTh-WD,LTh-DBH and WD-DBH in 2011 and 2021 have significant relevance at each community level.The plants in 2021 tend to allocate limited resources to traits related to photosynthesis(SLA),rapid growth(DBH)and environmental stress defense(WD)as compared with 2011.Similarly,SLA-DBH,SLA-LTh and LTh-WD showed a significant correlation at the individual,species and community level,without scale dependence,and the slope was significantly different from 1,showing an allometric growth strategy.However,SLA-WD,LTh-DBH,WD-DBH,LTP-WTP(Leaf total phosphorus,LTP;Wood total phosphorus,WTP),and LSS-WSS(Leaf soluble sugar,LSS;Wood soluble sugar,WSS)changed with the change of community organization level,reflecting the scale dependence of these functional traits.In addition,the individual-level traits were sensitive to the environment.