Study On The Regulation Mechanism Of Different Grass-managements Practices To Soil Carbon Pool Behavior And The Response Of Plant Photosynthesis In Apple Orchard

This study was aimed to investigate the effect of wildly growing-grass with different fertilizers (nitrogen, phosphorus and potassium) activity and different treatments (trampling, pressing and mowing) on the characteristics changes of carbon pool behavior in wildly growing grass apple orchard of cold climate region, and to further illuminate the varying pattern and the mechanism of carbon cycle. For this purpose, the soil organic carbon (SOC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC), microbial biomass carbon (MBC) content combine with the soil enzyme activities which take part in the carbon cycle such as cellulase, β-glucosidase, invertase were measured at soil depths of 0-20 cm, 20-40 cm and 40-60 cm, respectively. Moreover, the functional diversity of soil microbial communities were cleared, and the photosynthetic physiological responses of apple plants were detected. The main results were as follow:1. In the fertilizers test and different grass managements, the soil organic carbon (SOC) content decreased gradually with the increase of soil depth, with the change of month, the soil organic carbon content displayed increase first and then decrease, July was the highest. In the fertilizers test, compared to wildly growing grass, fertilizers applying increased the SOC content significantly, and applied nitrogenous (N) fertilizer was more obvious. In the different grass managements test, the SOC content of each soil depth had increased significantly after mowing. From June to September, the SOC content of 0-20 cm soil depth were 12.73%, 16.05%,14.44% and 26.94% higher than that of control. The pressing treatment also increased the SOC content, but less effective than the mowing treatment, meanwhile the trampling treatment had no significant effect.2. In the treatment of two kinds of experiments, dissolved organic carbon (DOC), easily oxidized organic carbon (EOC), microbial biomass carbon (MBC) content had the same seasonal changes. The difference was the highest MBC content appeared in August, while the highest DOC and EOC content appeared in July. In the fertilizers test, applied nitrogenous (N) fertilizer increased the MBC and DOC content; the EOC content of shallow soil (0-20cm,20-40cm) was increased respectively by 9.84% and 7.40% than control only in July and August. In the different grass managements test, mowing treatment increased the MBC, DOC and EOC content significantly. The pressing treatment increased the DOC content of shallow soil, and lower than mowing treatment.3. During the whole test, soil enzyme activities of different treatment of experiments decreased gradually with the increasing of soil depth. Compared to control, various fertilizer treatments enhanced the soil enzyme of shallow soil clearly in July, August and September. Applied nitrogenous had obvious effects on soil invertase activity; soil cellulase activity and β-glucosidase of various fertilizer treatments significantly increased and the results showed nitrogen fertilizer>phosphorus fertilizer>potassium fertilizer. Mowing increased the three enzyme activities of 0-20 cm soil depth significantly, from July to September, soil invertase activity was increased by 12.49%,15.98% and 13.02% respectively compared to control. In July and August, pressing treatment increased β-glucosidase activity of 0-20 cm soil depth significantly.4. The results of Biologic micro plate analys is showed that the soil population diversity (AWCD), and the utilization of carbohydrates, amino acids and polymerid were significantly increased after fertilizers applying, compared to control, the nitrogen treatmentwas most obvious. Applied nitrogenous (N) fertilizer could also significantly increase Shannon richness index (S) and Shannon diversity index (H), while applied phosphorus (P) fertilizer increased Shannon diversity index (H) and Evenness index (E). Using Principal Component Analysis (PCA), this paper showed that fertilizers applying made the stability of soil microbial communities decreased. In the different grass treatments test, mowing treatment significantly increased the soil population diversity (AWCD), Shannon richness index (S) and Shannon diversity index (H), but pressing and trampling treatments made Evenness index (E) decreased of which the utilization of carbohydrates, phenolic acid and amines were higher only in mowing treatment. Other two treatments made the stability of soil microbial communities decreased.5. Various fertilizer treatments had no significant effects on soil respiration rate. The highest soil respiration rate of various fertilizer treatments appeared in August, soil respiration rate of applied nitrogenous (N) fertilizer was higher than control significantly, while other treatments were not. The trampling, pressing and mowing treatments had no obvious significance on soil respiration rate.6. During the whole test, various fertilizer treatments and trampling, pressing, mowing had no obvious effects on photosynthetic capacity of apple trees.7. Compared to control, applied nitrogenous (N) fertilizer and mowing treatment improved soil organic carbon content effectively, enhanced the several key enzymes activity involved in carbon cycle, and also increased the utilization of carbon source of soil microorganism. Therefore, applied nitrogenous (N) fertilizer and mowing treatment can be used as the feasible management measures of wildly growing grass orchard.