Distribution Characteristics Of Nutrient Elements In Pinus Sylvestris Var. Mongolica Plantations With Different Stand Ages

Pinus sylvestris var.mongolica is the main forestation tree species of protective forest in China.However,some introduced P.sylvestris var.mongolica has declined and died with the development of forest plantations.Nutrient elements are the main limiting factors for plant growth,and their distribution pattern is an important factor for maintaining the forest structure and function stability.In this study,the distribution characteristics of carbon,nitrogen,phosphorus,potassium,calcium,magnesium,iron,zinc and manganese in different organs(needles,branches,trunks,coarse roots and fine roots)and soils in 15-,25-,34-,47-,55-and62-year-old P.sylvestris var.mongolica plantations were analyzed,and the relationships of nutrient elements between plants and soil were explored.The main research results are as follows:(1)With increase of stand age,the carbon contents in trunks and coarse roots,phosphorus content in current year branches,and calcium content in fine roots decreased,while the nitrogen content in one-year-old branches and calcium content in two-year-old branches increased;The phosphorus contents in two-year-old branches and fine roots,and potassium contents in current year branches and fine roots firstly decreased and then increased,the calcium contents in current year and one-year-old needles,magnesium content in needles,iron contents in two-year-old needles and fine roots,and zinc contents in two-year-old needles and one-year-old branches,manganese contents in current year and two-year-old needles and branches,and coarse roots firstly increased and then decreased.The carbon content was the highest in the needles,and the iron content was the highest in the fine roots.The phosphorus content was the highest in the current year needles of 25-,34-,47-and 55-year-old P.sylvestris var.mongolica.The calcium content was the lowest in the trunks of 15-,25-,34-and 55-year-old P.sylvestris var.mongolica.The magnesium content was the lowest in the trunks of 15-,25-,34-,55-and 62-year-old P.sylvestris var.mongolica.The zinc content was the lowest in the trunks of 15-,34-,47-,55-and62-year-old P.sylvestris var.mongolica.Manganese content was the lowest in the trunks of 15-,25-,47-and 62-year-old P.sylvestris var.mongolica.(2)With increasing stand age,the contents of organic carbon,total nitrogen,total phosphorus,potassium,calcium,magnesium and manganese in 0–10 cm soil layer firstly increased and then decreased.With the increase of stand age,the total nitrogen content in the10–20 cm soil layer decreased,while the contents of total nitrogen,total phosphorus,iron and manganese in the 20–40 cm soil layer firstly increased and then decreased,but the zinc content firstly decreased and then increased.Soil organic carbon content decreased with the soil layer in the 47-and 62-year-old P.sylvestris var.mongolica plantations.Soil total nitrogen content decreased with the soil layer in 15-,25-,34-,47-and 55-year-old P.sylvestris var.mongolica plantations.Soil available phosphorus content decreased with the soil layer in 25-year-old P.sylvestris var.mongolica plantations.Soil calcium content decreased with the soil layer in47-year-old P.sylvestris var.mongolica plantations.(3)Soil organic carbon content was positively correlated with needle phosphorus content,but negatively correlated with fine root phosphorus content in P.sylvestris var.mongolica plantations.Soil total nitrogen content was positively correlated with needle nitrogen and phosphorus contents and branch nitrogen and phosphorus contents.Soil calcium content was positively correlated with needle and coarse root manganese content.Soil magnesium content was positively correlated with needle manganese content and branch and fine root magnesium content.Soil iron content was positively correlated with needle,coarse root and fine root magnesium content,and branch and fine root zinc content.Manganese content in soil was positively correlated with manganese content in needles,branches and coarse roots.