Abstract: In order to approach the seasonal dynamics of soil microbial biomass and enzyme activities in different sand-fixation plantations on Horqin sandy land, 25-year old Caragana microphylla, Hedysarum fruticosum, Artemisia halodendron and Pinus sylvestris var. mongolica plantations were selected, with the seasonal variations of the protease, urease, saccharase, phosphomonoesterase, polyphenol oxidase, nitrate reductase, and dehydrogenase activities as well as the microbial biomass C, N and P in 0-30 cm soil layer studied. The results showed that the activities of the seven enzymes in the four plantations varied significantly with season, i.e., increased gradually in spring, reached the maximum in summer, and decreasing in autumn and winter, with the variation degree being more significant in 0-10 cm soil layer than in other soil layers. The enzyme activities and microbial biomass were the highest in 0-10 cm soil layer, and decreased down the profile. Among the four plantations, C. microphylla had the highest soil enzyme activities and microbial biomass, with the highest capability in improving the biological activity of sandy soil.

Key words: Long term nitrogen fertilization, Chlorophyll fluorescence, Winter wheat, Dryland