| In this paper, we used three paddy soils with different nitrogen status to investigatethe effect of fertilization on ecological characteristics of soil microorganism. The fourdifferent fertilization treatments, included control (CK), inorganic fertilizer (CF), pigmanure in combination with inorganic fertilizer (PM) and straw manure in combinationwith inorganic fertilizer (RS). Information provided in this work might contribute to abetter understanding of soil fertility in paddy environment. Main original conclusions wereshown as follows.①The laboratory incubation experiment was carried out to elucidate the effects offertilization on soil microbial biomass. The results showed that fertilization caused asignificant ascendance in soil microbial biomass carbon (Cmic). Cmic were significantlyhigher in RS and PM treatments compared to the CF or CK (P＜0.05). During the 14-42days incubation, the microbial biomass reached their maximum values in the fourtreatments separately and then started to decline. Obviously, these results showed thatorganic manures had longer effects on microbial biomass than inorganic fertilizers, wefound that the Cmic were closely correlated to total nitrogen of the soils. Meanwhile, platecounts also supported that there were more microorganisms in organic manure treatmentsthan that in CF and CK treatments. These were similar trend with diversification ofmicrobial biomass. The amount of the Bacteria and Fungi were greater in RS and PM thanCK and CF, whereas the Actinomycetes were greater in CK and CF. Soil microbialbiomass carbon might be a sensitive indicator reflecting soil fertility level.②Enzymatic activities of the three soils with different fertilization were investigated.The results indicated that the enzymatic activities of urease in PM,RS and CF were higherthan in CK (P＜0.05) at any time during incubation, fertilization appeared to enhance theenzymatic activities of urease. During the five weeks incubation, the enzymatic activitiesof urease reached maximum values in the four treatments simultaneously; this was notconsistent with microbial biomass. We also found that the enzymatic activities of ureaseclosely correlated to soil total nitrogen. The enzymatic activities of acid phophatase weresimilar with the urease, but the former were steadier. It suggested that the fertilization hadless influence on acid phophatase than urease. These results showed that the enzymaticactivities of urease and acid phophatase were sensitive biological indicators to reflect soilfertility. The enzymatic activities measured using fresh soil were generally higher than that measured using air-dried sample. It seemed that soil fertility indices were more closelyrelated to enzymatic activities in the fresh soil than in the air-dried sample.③Two measurements based on microbiological community, namely, communitylevel physiological profiling (CLPP) using Biolog sole C source utilization tests andphospholipid fatty acid (PLFA) profiles were used to investigated the diversity ofmicrobial community of soils with different fertilization. The results of the functionaldiversity of soil microbial community indicated by BIOLOG ECO plates showed that soilmicrobial metabolism quotient (AWCD), Shannon index and McIntonch index allincreased significantly in RS and PM compared with CK, while the former reduced thenumber of utilized carbon resources. Soil microbial population and functional diversities ofmicrobial community have changed to some extent under different fertilization. Principlecomponent analysis of sole carbon source utilization pattern also demonstrated thatfertilization had significantly affected soil microbial community structure and changed theprofiles of C source utilization. The results of phospholipid fatty acid (PLFA) analysis alsorevealed changes in the composition of the microbial communities after differentfertilization. The profiles of 30 phospholipid fatty acids (PLFAs) were used to assesswhether observed changes in composition microbial parameters were accompanied bychanges in the composition of the microbial communities after different fertilization. Theresults showed that the relative amounts of PLFAs were obviously different among thefour different fertilization treatments, and fertilization might increase the PLFA biomarkersfor Bacteria and Fungi, while reduced Actinomycetes and the ratio of Gram-positive toGram-negative bacteria. The ratio of G~+/G~- was significantly higher in CK and CFcompared to the RS and PM (P＜0.05). The results of principal component analyses(PCA) indicated that the composition of the microbial community was also altered bydifferent fertilization, However, further studies will be needed to better understand howthese changes in microbial community structure might actually impact soil microbialcommunity function.
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