Ecological Stoichiometry Characteristics Of Pinus Sylvestris Var. Mongolica Plantation In Sandy Land Under Different Densities

Pinus sylvestris var.mongolica was the main shelter forest species in China.With the growing area of Pinus sylvestris var.mongolica plantation,some large density Pinus sylvestris var.mongolica plantations had declined and died.In order to explore the effect of density on Pinus sylvestris var.mongolica plantation.In this study,six densities(490 stems·hm^-2,750stems·hm^-2,1110 stems·hm^-2,1550 stems·hm^-2,1930 stems·hm^-2,2560 stems·hm^-2)of Pinus sylvestris var.mongolica plantation in Horqin sandy land were used as the research objects.The stoichiometric characteristics of C,N and P in plant?leaf,branch and root?-litter-soil were studied.The seasonal dynamics of C,N and P contents and their stoichiometric ratios were analyzed.The correlations between the stoichiometry of C,N and P in soil and leaf,branch,root and litter were discussed.The main results were as follows:.?1?Stand density had a significant effect on C,N and P contents and their ratios of Pinus sylvestris var.mongolica plant-litter-soil.When stand density was 1100-1550 stems·hm^-2,the C:P and N:P of plants were lower,which indicated that the growth of trees was good.The contents of organic carbon,total nitrogen and total phosphorus in the soil were higher,which indicated that the soil had a certain improvement effect.The litter needles havd high nutrient content and good illumination conditions,which was beneficial to the synthesis and transformation of plant and soil nutrients.The stand density was suitable for the growth of Pinus sylvestris var.mongolica.?2?The changes of C,N and P contents and their ratios with density of Pinus sylvestris var.mongolica plants and soils were different in different seasons.With the increase of stand density,the contents of nitrogen and phosphorus in plant organs increased first and then decreased in April and June,while C:N and C:P decreased first and then increased,and the contents of soil nutrients increased first and then decreased.In August,the nitrogen content in branches of all ages decreased first and then increased,the phosphorus content in plant organs increased first and then decreased,and the soil nutrient content increased first and then decreased.In October,the contents of carbon,nitrogen and phosphorus in current-year and one-year-old branches increased first and then decreased.Soil organic carbon and total phosphorus decreased first,then increased and then decreased,while soil total phosphorus,available nitrogen and available phosphorus increased first and then decreased.?3?There is a significant correlation between C,N,P contents and their ratios in the plant-litter-soil system of Pinus sylvestris var.mongolica,which indicates that there is a transport transformation among the three pools of plant,litter-leaf and soil in the ecosystem of Pinus sylvestris var.mongolica under different densities.