Effects Of Afforestation Density On Distribution Of Nutrient Elements In Pinus Sylvestris Var.Mongolica Plantation

Pinus sylvestris var.mongolica is the most important evergreen coniferous tree species in three-north shelterbelt project in China.Stand density determines the spatial structure of stand and is an important factor affecting the growth of trees.Distribution pattern and accumulation law of nutrient elements are important aspects to maintain the stability of forest structure and function.Studying the distribution characteristics of nutrient elements in Pinus sylvestris var.mongolica plantations with different densities is helpful to understand the nutrient balance and circulation law of Pinus sylvestris var.mongolica plantations and provide reference for determining optimum afforestation density and sustainable management.In this study,P.sylvestris var.mongolica plantations with different densities(490,750,1110,1550,1930 and2560 plants·hm^-2)were selected as the research objects,the distribution of carbon（C）,nitrogen（N）,phosphorus（P）,potassium（K）,calcium（Ca）,magnesium（Mg）,iron（Fe）,zinc（Zn）,and manganese（Mn）in different organs（needle,stem,trunk and root）,litters and soil of Pinus sylvestris var.mongolica were analyzed,and the relationships among nutrient elements of plant-litter-soil were discussed.The main results were as follows:（1）With the increase of density,the contents of C,N and P in each organ firstly increased and then decreased.C content was highest at 1110-1550 plants·hm^-2,but the contents of N and P was highest at 1550 plants·hm^-2.K content in each organ was highest at 2560 plants·hm^-2,the contents of Ca,Mg and Fe were highest values at 750 plants·hm^-2,and the contents of Zn and Mn were highest values at 1930 plants·hm^-2.The contents of N,P,Ca,Mg and Mn followed the order of needle and stem>trunk and root,the contents of K and Zn followed the order of fine root>needle and stem>coarse root and trunk,and the content of Fe followed the order of root and trunk>needle and stem.（2）The contents of C,N and P in litter were highest at 1550 plants·hm^-2.K content in litter was highest at 2560 plants·hm^-2,the contents of Ca,Mg and Fe were highest at 750 plants·hm^-2,and the contents of Zn and Mn were highest at 1930 plants·hm^-2.With the increase of density,N resorption efficiency firstly increased and then decreased,it was highest at 750 plants·hm^-2.The resorption efficiencies of P and Mg firstly decreased and then increased,they were highest at 2560 plants·hm^-2.K resorption efficiency firstly increased and then decreased,it was highest at 1550 plants·hm^-2.Ca resorption efficiency decreased,it was highest at 490 plants·hm^-2.Fe resorption efficiency firstly decreased and then increased,it was highest at 450 plants·hm^-2.The resorption efficiencies of Zn and Mn firstly increased and then decreased,they were highest at 1110 plants·hm^-2.（3）With the increase of density,the contents of soil organic carbon（OC）,total nitrogen（TN）,total phosphorus（TP）,available nitrogen（AN）,available phosphorus（AP）and Ca in different soil layers firstly increased and then decreased,they were highest at 1550plant·hm^-2.The contents of K and Mg in 0-20 cm soil layer were highest at 1550 plants·hm^-2.The contents of Fe,Zn and Mn firstly decreased and then increased,they were lowest at 1110-1550plants·hm^-2.The contents of OC,TN,TP,AN,AP,Ca and Zn decreased with the deepening in the soil layer.（4）The relationships between needle and litter in contents of C,N,Ca,Mg,Fe,Zn and Mn were positively correlated.The contents of soil TN and AN were positively correlated with the contents of N in needle,litter and fine root,the content of soil TP was positively correlated with the content of P in needle,the content of soil AP was positively correlated with the content of P in litter and fine root,and the content of soil Zn was positively correlated with the content of Zn in needle,litter and fine root.