Characteristics Of Vegetation Community And Soil Nutrient Changes During Secondary Succession Of Tropical Lowland Rain Forest In Hainan

It is of great scientific significance to study the vegetation characteristics and soil environment of secondary forests at different succession stages in tropical regions for mitigating climate change,protecting biodiversity and restoring and protecting rare species.Ganshiling is a typical tropical lowland rain forest with rare species as Hopeareticulata.The plant species and distribution have their particularity,which provides a favorable condition for the study of tropical vegetation.However,due to the impact of climate change and human activities in the past,large areas of tropical lowland rain forests in the protected areas have been cut and destroyed to varying degrees,endangering endangered species and facing severe tests of biodiversity.In order to better promote the restoration of vegetation and rare species in the protected area,this study plans to choose the Ganshiling Ecological Station to study the vegetation and soil of tropical lowland rain forest.Four vegetation communities at different restoration stages(herb community,shrub community,secondary forest with40 years,secondary forest with 60 years)were selected in Ganshiling Natural Reserve.Through field vegetation investigation,root biomass(0?10 cm)and soil sample collection(0?60 cm)at different depths,and combined with laboratory experiments on soil physical and chemical properties and soil enzyme activity,the method of space instead of time was adopted to mainly study:(1)Changes in species composition and diversity at different succession stages after human disturbance and their effects on rare and protected species;(2)The variation characteristics of root biomass of tropical lowland rain forests in different succession stages;(3)Characteristics of soil physicochemical properties and microbial changes during secondary succession in tropical lowland rain forests and their influencing factors.The aim is to provide an important basis for the protection and restoration of the rainforest ecosystem and the rare species,as well as the scientific management in the future.The main research results are as follows:(1)A total of 205 species of vascular plants,belonging to 176 genera and 93families,were recorded in this study.Forest succession significantly changed the species composition and vegetation characteristics of the community.In the early stage of succession,it was mainly composed of perennial herbs and ferns,while in the late stage of succession,the importance value of dominant species in the community decreased gradually,but the species distribution was more uniform.Along the species succession gradient,the species substitution increased firstly and then decreased among the adjacent communities,and developed from extremely dissimilar in the early stage of succession to moderate similarity in the later stage of succession and the community structure tended to be stable.In addition,the number of species,species richness(S),biodiversity index increased with the positive succession of the community,and there were significant differences among different succession stages.There was a positive correlation between species diversity(?)and the abundance of rare and protected species.Rare and protected species generally distributed in the middle and late stages of high biodiversity succession,and the rare and protected species also had a higher contribution to biodiversity.(2)The total biomass in the root system of 0?100 cm at different succession stages in the tropical lowland rainforest of Ganshiling ranged from 5.23 to 28.98 t·hm^-2.Vegetation succession significantly increased root biomass and changed root structure.With the increase of soil profile depth(0?100 cm),the root biomass of the herbaceous community decreased significantly.The vertical variation of root biomass in the soil profile showed exponential regression,while the other stages of restoration and succession showed power regression.In the root biomass model,tree height and D²H had a higher degree of fitting with root biomass,while DBH and tree height were the main factors affecting root biomass.In practice,the root biomass of vegetation can be estimated according to tree height and D²H in Ganshiling region,which can provide underground data support for the ecological restoration of communities at different succession stages and the development,change and protection of rare and protected species in the region.(3)The restoration and succession of tropical lowland rain forest in Ganshiling significantly affected the contents of SOC,TN,TP,extracellular enzyme activities and their stoichiometric characteristics in the topsoil(0?10 cm).With the progression of succession(positive),the overall SOC and TN of different soil depth at each succession stage showed an upward trend,while the overall TP showed a downward trend.Soil extracellular enzymes AP and NAG+LAP also showed an increasing trend,while BG showed a decreasing trend at first and then an increasing trend.Soil stoichiometry showed an increasing trend in general and reached the maximum value in the later stage of succession.With the deepening of soil layer,soil C,N and P contents and stoichiometry both showed a decreasing trend,and the differences between different stages of succession gradually decreased.The results showed that root biomass and soil depth were the main factors regulating the soil C,N,P and stoichiometric characteristics at different depths in this region.The changes of soil extracellular enzyme activities and their stoichiometry were mainly affected by the changes of biological factors and abiotic factors,soil C:P,N:P,moisture content,root biomass,DBH and litter were the main influencing factors of soil enzyme activities in different succession stages.The comprehensive contribution rate of abiotic factors was higher than that of biological factors,and the changes of soil extracellular enzyme activities and stoichiometric characteristics in different succession stages were more easily explained by abiotic factors directly.(4)Soil stoichiometry showed that topsoil(0?10 cm)was mainly restricted by N and P,limiting factors would change with the succession.The succession of tropical forest further aggravated the P limitation of topsoil,but alleviated the N limitation to some extent.It was mainly restricted by N in the early and middle stages of succession,but with the progression of succession,N limitation gradually decreased and P limitation gradually increased,and P eventually became the main limiting factor in the late stage of succession.In addition,the soil extracellular enzyme stoichiometric ratio showed a general downward trend.The average ratio of Ln(BG):Ln(NAG+LAP):Ln(AP)was 1:1.25:1.05,it deviated from the mean value of 1:1:1 in the global forest ecosystem and China.There was an imbalance between resource supply and production,and soil microorganisms were restricted by obvious N and P.The N restriction was greater than the P restriction,which was the main limiting factor.The succession alleviated the C and N restriction of microorganisms,but intensified the P restriction,which was basically consistent with the nutrient restriction in soil stoichiometry.