Responses Of Nutrient Contents Of Different Organs To Nitrogen And Phosphorus Fertilization In Pinus Elliottii Plantation

The experimental site is located at Dahe forest farm(25°58'N,119°40'E),Fujian,South-Eastern China,where 23 yrs Pinus elliottii plantation was selected.We seted four treatments(CK,+N,+P,+NP)at forest.Every treatment had four repetitions,sixteen 30 mX30m plots were established at forest.Measuring nitrogen(N),phosphorus(P),calcium(Ca),magnesium(Mg)concentrations of the foliages(in different foliar ages),branches(in different branches ages),fine roots(in different orders),and soil from each plots in order to explore the response of different organs nutrient content to nitrogen and phosphorus fertilization and deepen the understanding of the relationship between forest plants and soil.The main findings were as follows.(1)Analyzing the effects of nitrogen and phosphorus fertilization on nutrient content of different organs of Pinus elliottii,we could know that fertilization significantly affected litter,old branches and fine roots N concentrations;different treatments had significant effects on P concentration of branches and fine roots.But nitrogen and phosphorus fertilization had no significant effects on Ca and Mg concentration of any organ.(2)Nitrogen and phosphorus fertilization greatly affected mineral N concentrations in soil,which effectively alleviate the situation of soil nitrogen deficiency,but fertilization had no significant effects on total N,P,exchangeable Ca and Mg of soil.(3)After 1-year field experiment of nitrogen and phosphorus fertilization,new leaves and fine roots ?15N showed a tendency to +N treatment>control treatment>+P treatment,but had no significant differences.The effect of different treatments on soil 815N was significant,the soil ?15N of nitrogen fertilization treatment was significantly higher than other treatments.(4)Nitrogen and phosphorus fertilization had significant effects on the C:N in new leaf,the N:P in litter,the C:N and N:P in old branches,the C:N in fibrous roots,the C:N,N:P and C:P in new pioneer roots,which shown that litter,branches,and new pioneer roots N:P ratios are more responsive indicators of soil nutrient availability than other organs.(5)During 1-year field experiment of nitrogen and phosphorus fertilization,N contents of old branches and fine roots which all had significantly positive correlations with soil total N content;P concentrations of old branches and fine roots both had significantly positive correlations with soil total phosphorus.Linear regression analysis showed that old branches N content is a more responsive indicator of soil total N content than new pioneer roots,and fibrous roots P content is a more responsive indicator of soil total P content than new pioneer roots and old branches.