| Pinus massoniana is the preferred tree species for timber forests in China.At present,the contradiction between supply and demand of large-diameter timber in China is becoming increasingly prominent.Directional transformation of existing Pinus massoniana forest is of great significance in alleviating the contradiction between supply and demand of large-diameter timber.The experiment uses 25-year-old Pinus massoniana forest as experiment material,use general rotational regression design with four factors and five levels as the experiment method.In order to provide certain basic datas and experimental references for the directional breeding of Pinus massoniana,the experiment measured the increase in breast diameter of Pinus massoniana and the change of fine roots,leaves and soil nutrients,studied the effects of fertilization and density regulation on breast diameter growth of Pinus massoniana,learned the response to different treatments and changing characteristics of fine roots,leaves and soil nutrients,explored the relationship between fine roots,leaves,soil nutrients and breast diameter growth of Pinus massoniana.The conclusions of this experiment are as follows:（1）Nitrogen application had a significant effect on the breast diameter growth of Pinus massoniana,and the breast diameter growth increased with the increase of N application;the amount of nitrogen and potassium had a significant effect on the total N and K content of the soil.The total N and K content of the soil increased with the increase of the amount of N and K applied.Nitrogen application had a significant effect on N content of fine root,it increased with increasing nitrogen application.Phosphorus and potassium application had a significant effect on P content of fine root.The P content of fine root increased with the increase of the amount of phosphorus application,and showed a trend of increasing first and then decreasing with the increase of the amount of potassium application.Density regulation had little effect on the fine root and needle leaf nutrient content of Pinus massoniana.（2）Among the four factors studied,the interaction between the amount of nitrogen and potassium,the amount of phosphorus and the amount of potassium had a significant effect on the growth of Pinus massoniana breast diameter.The interaction between nitrogen application,phosphorus application and potassium application had a significant effect on the N content of fine root.The interaction of nitrogen application and phosphorus application had a significant effect on the P content of fine root.There are significant regression relationships between the four factors and the breast diameter growth,total soil N,P,K content and fine root N,P content.The fit is high and can be used for actual production prediction.（3）The nutrient contents of fine roots,leaves,and understory of Pinus massoniana showed obvious seasonal changes during the growing season.The nutrient contents of soil and leaves were higher from July to September,and the fine root nutrient contents were lower at this time,and higher at the end of the growing season.（4）Pinus massoniana breast diameter growth has no significant correlation with soil nutrients and leaf nutrients.The nutrient contents of leaves may be inappropriate for reflecting the growth of Pinus massoniana.The N and P contents of fine roots were positively correlated with breast diameter growth of Pinus massoniana,that is,the changes of fine root nutrients may better reflect the growth status of the trees.However,since fine roots are sensitive to changes in the external environment,this conclusion should be further studied to verify.To sum up,after one year of fertilization and density control on the existing Pinus massoniana plantation,N,P2O5,K2O and retention density had a certain effect on the growth of breast diameter diameter and the nutrient content of soil,fine root and needle.The effect of fertilization and density regulation on promoting breast diameter growth was better than density treatment only.Breast diameter growth was significantly correlated with the N and P content of fine root.The changes of soil nutrients and needle nutrients were consistent during the growing season,fine root nutrients were higher at the end of the growing season.Under the experimental conditions,the best experimental schemes for the cultivation of large-diameter timber of Pinus massoniana are N 450g/plant,P2O5900 g/plant,K2O 300 g/plant,retention density of 1050-1200 plants/hm2,and the theoretical annual growth of breast diameter is 0.7375 cm,the N content of fine root is 13.43 g/kg,and the P content is 0.4445 g/kg. |
