Ecological Stoichiometric Characteristics Of Populus Davidiana Forest With Different Degrees Of Growth Decline

The southern part of Daxing'an Mountains is located in the ecological transition zone between forest and grassland.The structure,function and ecological process of the ecosystem are quite complex.Its biological communities are very sensitive to climate change and are vulnerable to global climate change.In recent years,a large area of forest patch like death or growth decline has occurred in Saihanwula area in the southern part of Daxinganling Mountains,which may be due to the nutrient limitation during the growth of trees.In order to verify the hypothesis that the growth decline phenomenon of Populus davidiana forest in Saihanwula area of Southern Daxing'an Mountains of Inner Mongolia has a greater probability correlation with the nutrient limitation in the growth process of Populus davidiana,the research tool of ecological stoichiometry was used to study the growth decline phenomenon of Populus davidiana in Saihanwula area The contents of C,N and P in leaves,trunk,root,root zone soil and litter of Populus davidiana with different growth decline degrees were compared and analyzed.The main results are as follows:1.Effects of soil organic C,total N,total P and their stoichiometric ratio on the growth of Populus davidiana:In the study area,the contents of total N and P in the root zone of severely declining Populus davidiana were significantly lower than those of normal growth Populus davidiana;the contents of soil organic C and total N were higher than the average level of forest soil in China,and the total P content of soil was lower than the average level of forest soil in China(the main lack of P element);the N and P elements in soil mainly existed in the form of organic matter(the ratio of soil C/N and C/P was higher than that of soil organic matter)The critical point of decomposition is not conducive to the release of N and P elements.2.Response of C,N,P nutrient contents and their stoichiometric ratios in Populus davidiana litter:The contents of C,N and P in the leaves of Populus davidiana in the study area were within the average level of most terrestrial plants in the world and in China.The C/N ratio in the leaves of Populus davidiana was significantly higher than the critical point of nutrient N release,which was not conducive to the decomposition and release of N element;the C/P ratio of the leaves of severe growth decline poplar was significantly higher than that of the critical point of P nutrient release,which was notconducive to the decomposition and release of P element,which was related to the P content in the litter leaves of normal growth Populus davidiana was significantly higher than that of the severe growth decline Populus davidiana.3.Reabsorption characteristics of N and P nutrients in Populus davidiana:In this study,n reabsorption rate(54%)was higher than p reabsorption rate(45%);P reabsorption rate of Populus davidiana leaves was adapted to P deficiency in plant root zone soil(helpful to improve plant drought resistance and adaptability to arid environment).P reabsorption rate of normal growth Populus davidiana in the study area was significantly higher than that of heavily growing Populus davidiana.4.Response of C,N,P and their stoichiometric ratios in different organs of Populus davidiana:The results showed that the N and P contents of Populus davidiana in the study area were lower than the average level of plant living leaves in the world and the average level of plant living leaves in China,which reflected the growth rate of plants/N.C/P index was higher than that of normal growth Populus davidiana.Therefore,the growth process of Populus davidiana was limited by nutrients,which was related to the existence of N and P elements in soil in the form of organic matter and the decomposition rate of litter leaves.