Effects Of Different Forest Types On Plant Community Structure,Plant,Litter And Soil Ecological Stoichiometry

The Qinghai-Tibet Plateau,located in the southwest of China,is an important ecological security barrier in China and even Asia.There is a large area of forest in this region.However,due to climate change and irrational human activities,the area of primary forest decreased gradually,while the area of secondary forest and plantation increased gradually.This change will inevitably affect the nutrient cycling of its ecosystem,and then affect its stoichiometric characteristics.Therefore,to study the effects of different forest types on plant community structure,plant,litter and soil ecological stoichiometry in the Tibetan Plateau,and to lay a foundation for revealing the nutrient cycling mechanism of different forest types on the Tibetan Plateau,and to provide theoretical guidance for formulating effective forest management strategies.Based on this,we selected typical plots of three different forest types: primary forest(PF),secondary forest(SF)and artificial forest(AF),and analyzed the understory plant community structure,the C,N and P stoichiometry characteristics of leaf,litter and soil,soil enzyme activities and their relationships.The main results were as follows:(1)The characteristics of understory plant community structure: the species richness of shrub layer was highest in SF.Species richness of herb layer was highest in PF.The species abundance of both shrub and herb layer was highest in SF.The aboveground biomass of shrub and herb layer was consistent,and the SF had the highest biomass.The results showing the natural forest had a higher species diversity than the artificial forest.(2)Leaf,litter and soil ecological stoichiometry: the change trend of plant and soil C content was the highest in PF,but the highest of litter was SF.The change trend of N and P contents was consistent in plant,litter and soil,showing that highest in AF.Regardless of C:N,C:P and N:P,the change trend of plant and litter was consistent,showing the highest in PF and the lowest in AF.In addition,different forest types from PF to SF and AF,leaf N:P decreased gradually from 19.76 to 8.84.Soil C:N was the highest in SF,while C:P and N:P were the highest in PF.N recovery efficiency(NRE)and P recovery efficiency(PRE)were the highest in SF and PF,respectively.(3)Leaf stoichiometric homeostasis: for N content,PF and SF was ‘strictly homeostatic’,while that in AF was ‘weakly homeostatic’.For P content,no matter in PF,SF or AF,it was ‘strictly homeostatic’.For N:P,the PF and SF were ‘homeostatic’,while the AF was ‘strictly homeostatic’.The results showing compared with AF,PF and SF have better adaptability to environment.(4)The characteristics and influencing factors of enzyme activity: the invertase activity was highest in SF,the urease activity was not significant in different forests(P >0.05),and the phosphatase activity was highest in SF.Invertase activity was negatively correlated with urease,positively correlated with phosphatase,and positively correlated with urease and phosphatase activities.The results indicating forest types were important factors affecting enzyme activity.In conclusion,the community structure of understory shrub and herb plants,the contents of C,N,P and their ecological stoichiometric homeostasis and soil enzyme activities were significantly different in plant leaves,litter and soil in PF,SF and AF on Tibetan Plateau.Compared with AF,species abundance,species richness and aboveground biomass of understory shrub and herb communities were higher in PF and SF.Plant and soil C content was high,N recovery efficiency(NRE)and P recovery efficiency(PRE)were also high,soil invertase(INV)and soil phosphatase(ALP)activities were high.The plant growth of PF is restricted by P,and that of SF and AF is restricted by N.Therefore,the management and protection of PF and SF on the Tibet Plateau should be strengthened.