Abstract: In order to compare the change of soil aggregate stability and organic matter in different development stages of Chinese fir, three stands in youngaged, middleaged and mature stages were selected to measure soil total carbon, total nitrogen, dissolved organic matter, microbial biomass, aggregate size distribution and aggregate stability. The results showed that soil carbon content in topsoil decreased first and then increased from middleaged to mature development stage, and total nitrogen content in topsoil increased with development of Chinese fir plantation, however, total soil carbon content in 20-100 cm soil layer remained unchanged in all three development stages. Dissolved organic matter and microbial biomass decreased significantly with soil depth. Dissolved organic carbon (DOC) content in 0-20 cm soil layer decreased with the increasing stand age. Microbial biomass carbon (MBC) in middleaged stand in each soil layer was significantly lower than in youngaged and mature stands. There was a significant correlation between active organic matter and total carbon, total nitrogen, bulk density, pH and water content, to some extent, which suggested that soil active organic matter of Chinese fir plantation was affected by multiple soil factors. With development of Chinese fir plantation, macroaggregate of >5 mm and mean weight diameter (MWD) in each soil layer increased and aggregatedamaging rate decreased. The stability of aggregates declined with soil depth. The proportion of >0.25 mm waterstable aggregate, mean weight diameter and geometry weight diameter of deep soil in middleaged and mature stands were less than in youngaged stand, which indicated that the development of Chinese fir plantation promoted the stability of soil aggregates in subsoil. A significant positive correlation between soil aggregate stability and silt particle content, active organic carbon fractions, total carbon and total nitrogen was found. In conclusion, soil carbon and nitrogen were accumulated and soil structure was improved when Chinese fir plantation developed to mature stage.

Key words: isotonic salt stress, drought stress, photosynthetic characteristic, tomato, chloroplast ultrastructure.,