Characteristics Of Soil C,N,P Changes In Pinus Sylvestris Var.mongolica Plantation Of Different Stand Ages In Zhanggutai Sandy Land

Pinus sylvestris var.mongolica is the main tree species for constructing protective plantations in“Three North”?Northwest,North and Northeast of China?area.The effects of the growth and development process of Pinus sylvestris var.mongolica on soil C,N,P changes should be clarified,which can provide a theoretical basis for the management and sustainable development of plantations.In this paper,20 plots of Pinus sylvestris var.mongolica plantation?including young forest,middle-aged forest,mature forest and over mature forest?and 4 natural control grasslands in Zhanggutai area of Liaoning Province were used as the research objects to study the different growth stages of Pinus sylvestris var.mongolica plantation in sandy grassland.Using a combination of field surveys and laboratory analysis,the change of soil C,N,P and their influencing factors were studied in 0-100 cm soil layers of different growth stages after sandy grassland afforestation with Pinus sylvestris var.mongolica.The results showed that after sandy grassland afforestation,the soil organic carbon of middle-aged forest decreased,while other stand increased.The soil total nitrogen in 0-20 cm soil layers before the middle-aged forest was significantly lower than that of the grassland,and 0-10cm soil layer of the stand was significantly higher than that of the grassland after maturity,soil available nitrogen increased significantly in 0-40 cm soil layers.The content of total phosphorus recovered to the grassland level in the middle-age forest,and then increased slowly with the increase of stand age,and the increment of 10-100 cm soil layers is about 0.06-0.07 g·kg^-1.The content of available phosphorus in 0-100 cm soil layers of young and middle-age forest was significantly higher than that of grassland,and the increment of available phosphorus decreased with the increase of stand age.When Pinus sylvestris var.mongolica stands mature,the supply of available phosphorus in soil is less than the demand of trees,and the growth of trees is limited by phosphorus.The changes of soil organic carbon were mainly affected by soil phosphorus?total phosphorus and available phosphorus?and potassium?total potassium and available potassium?after establishing Pinus sylvestris var.mongolica is plantation in sandy grassland,and soil organic carbon were affected by soil fine particles,soil moisture content and bulk density in20-40 cm and 60-80 cm layers.The main influencing factors of soil nitrogen change were soil phosphorus and potassium,but the influence of soil physical properties was relatively small,the change of soil total nitrogen was only affected by soil fine particles and soil bulk density in 0-20cm and 80-100 cm soil layers respectively,and the change of soil available nitrogen was only affected by soil water content in 20-40 cm soil layer.The soil total phosphorus were mainly affected by soil bulk density and available nitrogen,and soil available phosphorus were mainly affected by soil organic carbon and p H.In a word,Pinus sylvestris var.mongolica plantation can significantly increase the content of soil organic carbon.The growth of Pinus sylvestris var.mongolica plantation in the middle and young stage is limited by nitrogen,and that in the mature and over mature stage is limited by phosphorus.The soil C,N,P change greatly in different soil depths.In the growth period of Pinus sylvestris var.mongolica stand,the artificial management measures should be taken properly to avoid the decline of the growth and development of Pinus sylvestris var.mongolica due to the restriction of nutrient conditions,so as to ensure the sustainable development of Pinus sylvestris var.mongolica plantation.