Studies On Dynamics Of Nutrient And Defense Material In The Process Of Leaf-expansion In Subtropical Evergreen Broad-leaved Forest

Plants and insect herbivores are integral to the forest ecosystem,playing important roles in food webs,nutrient cycling and energy transfer.Herbivory on leaves by insect is common in the forest,and plants have consequently developed multiple strategies against insect herbivores.The evolutionary relationship between herbivores and plants has resulted in an impressive variety of adaptations and interactions,and studies of that relationship have become a most interesting focus in evolutionary biology and ecology.Evergreen broad-leaved forest is the regional vegetation in eastern China,and differs from tropical and temperate forest in both species diversity and community structure.Although research into subtropical evergreen broad-leaved forest had been conducted from many perspectives,study of the interaction between plant and insect herbivores is rare.However,the interaction between plants and herbivores is very important for maintaining and restoring evergreen broad-leaved forest.In this study, plants in Mt.Meihuashan of Fujian province and the Tiantong region of Zhejiang province were investigated.Through field research,monitoring and data analyses in the lab,herbivory pattern diversity,leaf phenology,leaf traits,temporal and spatial patterns of herbivory were researched into.And the strategies plants used to battle herbivores were summarized according to the results,which are as follows:1 The study is on the 10 species grown in Mt.Meihua broad-leaved evergreen forest.Nitrogen content of leaf's dynamic characteristics are as follows:Vaccinium braeteatum Thumb.var.chinense,Adinandra millettii,Rhododendron latoucheae three plants leaf nitrogen content continue to fall as the time changes.Nitrogen content of Eurya weissiae,Eurya murieala leaves in the process of the leaf-expansion continue to increase.Camellia fraterna and Cyclobalanopsis myrsinaefolia leaf's nitrogen content in the process of the leaf-expansion,at first decrease and then reduce;some plant's nitrogen content leaves increase stable, including Dendrobenthamia angustata and Schima superba;and Cinnamomum porrectum leaf's nitrogen content fluctuate with the time. According to leaf phosphorus content dynamic changes characteristics,it can be divided into the following categories:the first category,three kinds of plant leaves including Vaccinium bracteatum Thumb.var.chinense,Adinandra millettii,Rhododendron latoueheae phosphorus content in the process of the leaf-expansion,keep reducing;the second category,in the process of the leaf-expansion,leaf phosphorus content continue to rise,Eurya weissiae is the representing plant;the third category,phosphorus content to increase and then reduced,including Camellia fraterna and Eurya muricala;the fourth category, Dendrobenthamia angustata and Cinnamomum porreetum,the phosphorus content fall at the beginning and then increased;the fifth category,leaves phosphorus content changes volatile,Schima superba and Cyelobalanopsis myrsinaefolia are the representations.In the process of the leaf-expansion,characteristics of dynamic changes of soluble sugar content are:First of all,as time changes,Eurya weissiae's leaf's soluble sugar content continue to reduce;Second,as time changes,the soluble sugar content continues to rise,including Vaccinium braeteatum Thumb.var.chinense, Rhododendron latoueheae;but as time changes,leaves soluble sugar content to rise further reduced,Dendrobenthamia angustata is this type;fourth category,as time changes,soluble sugar content of Schima superba leaves to reduce further increase; Finally,the leaves of soluble sugar content volatility changes,including Cinnamomum porrectum,Eurya muricala,Adinandra millettii,Cyclobalanopsis myrsinaefolia,Camellia fraterna.Leaf's soluble sugar content further reduce the rising trend in the completion of the leaf-expansion,that is a turning point,this is the adaptation theory of these plants according to the insects or temperature,moisture changes.2 The study on the 10 species of Mt.Meihua evergreen broad-leaved evergreen forest leaf defense material(tannin)indicate:Schima superba,Adinandra millettii,Dendrobenthamia angustata,in the process of the leaf-expansion,leaves continued lower tannin content;The second category,Cinnamomum porrectum and Cyclobalanopsis myrsinaefolia leaves tannin content at first increase and then declare in the process of the leaf-expansion;the third category,Vaccinium bracteatum Thumb.var.chinense and Eurya weissiae the tannin content increase and maintain stability in the process of the leaf-expansion;the last,three plants including Eurya muricala,Camellia fraterna,Rhododendron latoucheae,tannin content have volatile changes.3 In the process of the leaf-expansion,the 10 species' nitrogen content of Mt.Meihua evergreen broad-leaved evergreen forest range from 4.012mg/g to 9.876mg/g,it is lower than Tiantong evergreen broad-leaved plants nitrogen content (6.49-14.69 mg/g).Mt.Meihua evergreen broad-leaved forest leaves 10 species in the process of the leaf-expansion,the phosphorus content in the 1.046mg/g to 2.556mg/g, and higher than the Tiantong leaf evergreen broad-leaved plants phosphorus content (0.66—1.13 mg/g).Leaf nutrogen content is lower than the country's 14.1mg/g,as well as the global level 20.6 mg/g;leaves phosphorus content is higher than the global level.Soluble sugar content of 10 species in evergreen broad-leaved forest in the process of leaf-expansion is between 0,30mg/g to 1.235mg/g.4 Mt.Meihua 10 kinds of leaves of evergreen broad-leaved plants in the process of the leaf-expansion,the tannin content range from 0.281mg/g to 2.569mg/g.The average is 0.6586mg/g,and is the same with temperate,tropical dry forest,tropical moist forest 282 kinds of plant leaves.5 According to this study in the process of the leaf-expansion,the nutrient content and defense material is inversely proportional,The end of the leaf-expansion was a turning point.When the nitrogen content and tannin content is a negative correlation,soluble sugar and tannin are positively correlated,and the phosphorus content and tannin always have a positive correlation.6 Four strategies were identified according to the results mentioned above.(1) The species that leafed out earlier with lower leaf nutrients content,higher defense material and lower leaf expansion rate,might employ 'defense' strategy to reduce leaf losses.(2)The species that leafed out earlier with lower leaf nutrients content, higher defense material and lower leaf expansion rate might employ 'escape' strategy to reduce herbivory.(3)The species that leafed out with higher leaf nutrients content,higher defense material and lower leaf expansion rate,might employ 'defense' strategy to reduce leaf losses.(4)The species that leafed out earlier with higher leaf nutrients content,lowerer defense material and lower leaf expansion rate. Higher leaves nutrients can attract more insects,and their chemical defense material failed or inadequate to turn to physical defense.Turn to using rapid growth or other ways to avoid herbivory.