Abstract: Soil samples were collected from the plow layers at two long-term experiment sites in Xinhua and Ningxiang counties of Hunan Province, China to study the effects of long-term fertilization on  organic nitrogen, microbial biomass, and microbial functional diversity of paddy soils. Long-term fertilization showed great effects on the soil N content. Compared with CK, treatments NPK plus manure or straw increased the contents of soil total acid-hydrolysable N and its fractions amino sugar N, amino acid N, and ammonium N. Treatment NPK had no significant effects on soil microbial biomass C and N, but trea tments NPK plus manure  increased the contents of soil microbial biomass C and N significantly. BIOLOG test showed that treatments NPK plus manure  enhanced the carbon utilization efficiency of soil microbes, and improved the  functional diversity of soil microbial communities, compared with CK. Long-term different fertilizer treatments resulted in the differences of carbon substrate utilization patterns of soil microbial communities.

Key words: long-term fertilization, paddy soil, organic nitrogen, microbial biomass, functional diversity, Haloxylon ammodendron, H. persicum,  chlorophyll fluorescence, dehydration stress, diurnal variation.