The Variation Characteristics And Mechanisms Of Soil Cellulase Activity In Different Developing Stages Of Chinese Fir Plantations

Using young forest, middle-aged forest, mature forest, and over-mature forest fir plantations in Dagang Mountain of Jiangxi Province as objects; we studied the variation characteristics of soil cellulase activity at varying developmental stages. Mechanisms of changes in cellulase absolute activities were further explored using the specific enzymatic activity concept and kinetic methods. Results showed1) throughout the development process of fir plantations, soil organic carbon, and microbial biomass showed significant changes in the law. Including soil total N, available nitrogen content, available potassium content, microbial biomass, as well as the soil porosity, field capacity, soil pHysical and chemical properties show a higher status on the stage of young forest, and decreased on middle-aged forest, on the mature forest they were significantly improved, to over-mature forest stage reach the highest level of the entire growth and development stage. Soil available pHospHorus content only in middle-aged-mature forest stage shows a significant increase. The principal component analysis showed that the soil fertility of Chinese fir plantation and most of the soil pHysical and chemical and biological indicators of soil quality, showing a young forest to middle-aged forest declined, from the age of forest to mature forest increased significantly, to the mature forest soil fertility achieved the highest level. The activity of cellulose is one of the most important factors regarding the soil fertility of fir plantations.2) Soil cellulase catalytic enzymatic reaction rate is the fastest between0and4hours, thenreduced gradually. To24hours the reaction rate has been close to0. So0to4hours can be considered as the initial velocity pHase of the soil cellulase enzymatic reaction. During development stages of the Chinese fir plantation, soil cellulase activity showeda significant decline fromthe young forest to middle age forest. By mature stage, cellulase activityraised significantly. To over-mature forest, it continued to rise. Cellulase activity and other soil pHysical and chemical indicators except soil available potassium showed significant or highly significant correlation, and the number of microorganisms in the soil and the number of bacteria was correlated with cellulase activity significantly, reflecting the soil of Chinese fir plantation cellulase activity is very sensitive to changes in soil quality, as one of the indicators to measure soil quality of Chinese fir plantation soil.3) Mechanisms of the changes in cellulase absolute activities in Chinese fir plantations varied at different developmental stages:From the young to middle-aged stage, a significant decrease in cellulase amount led to a sharp reduction of cellulase absolute activity, despite an increase in cellulase-substrate affinity. In the middle-aged to mature stage, cellulase amount were the most important affecting factors of absolute activity. In the over-mature stage, cellulase amount and cellulase-substrate affinity both promoted the highest levels of absolute activity. During the entire growth period in Chinese fir plantations, soil microorganisms were the main sources of cellulose, and the microbial biomass determined cellulase amount. Soil clay content affected cellulase-substrate affinity by changing the existing state of cellulase in the soil.