Investigation On Soil Carbon And Its Influence Factor In Different Developing Stages Of Chinese Fir Plantations

Soil organic carbon (SOC), soil respiration rate and soil properties in different developing stages of Chinese fir plantations were studied in Dagang mountain of Jiangxi Province and their variation characteristics of soil properties was investigated. Correlation analysis, stepwise regression analysis and path analysis were used to investigate the influence of soil factors on SOC content and soil respiration rate.The results were as follows:The entire developing process of Chinese fir plantations, the significant regular variation of SOC content, soil respiration rate and soil properties were found. SOC content decreased with increasing soil depth. Significant variation characteristics of SOC content were found in different soil layers, with coefficient variation in the order of 40-60 cm>20-40 cm> 0-20 cm, especially in the medium forest soil. With the growth and development of Chinese fir plantations, SOC content decreased from juvenile to medium, and then increased from medium to over-mature.Soil respiration rate ranged from 0.51μmol·m-2s-1 to 1.14μmol·m-2s-1, and it decreased first and then increased from juvenile to near-mature, slightly increased from near-mature to mature, and significantly decreased in the over-mature forest soil. Content of soil total nitrogen, alkali-hydrolyzable nitrogen, and readily available potassium, as well as the number of bacteria, fungi and actinomycetes showed higher values in the juvenile forest soil, a minimum in the near mature forest soil and significant increase in the mature forest soil and a maximum in the over mature forest soil. Soil available phosphorus content significantly increased from near mature to mature, but there were no changing regularity in other developing stages. With increasing stand age, annual litterfall amount and soil cellulase activity increased gradually, invertase activity decreased first and then increased, and amylase activity had no significant change.SOC content and the direction of decomposition and transformation were affected by direct and indirect effects of soil properties, but their influence mechanism are different. Alkali-hydrolyzable nitrogen content, the number of bacteria and fungi were determined largely by the variation of SOC content, and there are leading factors influencing SOC content variation. The positive direct effects of available phosphorus content and the number of actinomycetes were counteracted by the negative indirect effects on them, so showed less decisive degree of SOC content. Total porosity and readily available potassium also showed certain direct effects on SOC content, but influence degree was comparatively small. Soil respiration rate was affected by soil properties to different degree. Annual litterfall amount, soil organic carbon content and soil cellulase activity showed stronger direct and indirect effects on soil respiration rate.Compared with correlation analysis and stepwise regression analysis, path analysis can objectively and comprehensively assess the influences of soil properties on SOC content soil respiration rate.SOC content and soil respiration rate was affected by forest healthy condition to different degree. The pilot results were as follows:Juvenile was on the healthy condition, and SOC content and soil respiration rate were upper. With the variation of forest healthy condition, medium reached subhealthy condition, and SOC content and soil respiration decreased. Forest healthy condition recovered gradually from near-mature to mature, and SOC content and soil respiration rate increased gradually. Forest was on the health condition in over mature, and SOC content soil respiration rate reached to maximum, but soil respiration rate decreased to the level of medium.