Changes of soil microbial characteristics under long-term different land use patterns on an anthropogenic loess soil

【Objective】 As an important part of soil ecosystem, soil microbes could be influenced profoundly by different long-term land use patterns. 【Methods】 This research was based on the long-term trial of National Monitoring Base of Soil Fertility and Fertilizer Efficiency on Loess Soil in Yangling City, Shaanxi Province. Four treatments were chosen: farmland without fertilization(CK), farmland with N, P and K chemical fertilizer(NPK), abandoned land(AL) and fallow land(FL). The effects of long-term different land use patterns on soil microbial characteristics were studied by Biolog and routine analyses for the choice of rational landuse patterns and soil sustainable utilization in loess area, such as soil microbial biomass, soil respiration and soil microbial community functional diversity. 【Results】 The soil microbial biomass carbon(SMBC) and soil microbial biomass nitrogen(SMBN) in NPK and AL were higher than those in CK and FL significantly; There was no significant difference between NPK and AL in SMBC and SMBN, neither between the CK and FL. The highest ratio of SMBC to SMBN(SMBC/SMBN) was in NPK, and the lowest both in CK and FL; That was middle in AL, but no significant lower than NPK, neither not significant higher than CK and FL. The soil base respiration rate was in order of ALFLNPKCK, and the cumulative respiration was in order of ALNPKFLCK, which indicated that the soil microbial activity was the highest in AL, secondly in NPK, then in FL, and the lowest in CK. The results of Biolog analysis showed that the average well color development(AWCD) did no change significantly in AL, NPK and CK at the beginning of 24 h, then went up rapidly, while that in FL went up rapidly after 72 h. AWCD was the greatest in NPK and AL, then in CK, and the lowest in FL at the end of incubation. Shannon-Wiener richness index(H), carbon source utilization richness index(S) and Simpson index(Ds) were all the highest in NPK and AL, then in CK, and the lowest in FL. There was no difference in Shannon-Wiener evenness index(E) between treatments. Compared with CK, NPK and AL could significantly improve soil microbial structural and functional diversity, while FL had a negative impact on it. Five principal components were extracted from the principal component analysis, and their cumulative contribution of variance accounted for 87.7%, in which the variance contribution rates of the first principal component(PC1) and the second principal component(PC2) were 52.0% and 11.6%, respectively. NPK and AL were similar in carbon source utilization character by soil microbial communities, but significantly different with CK and FL, which means there was a significant differentiation on soil microbial community structure and function under different land use patterns. The carbon sources mostly used by soil microbes were carbohydrates, carboxylic acids and amino acids, which were the main carbon sources to distinguish different treatments. 【Conclusions】 Both abandoned land and farmland with rational fertilization could improve soil microbial biomass, soil respiration and soil microbial structural and functional diversity, while long-term absolute fallow land(No fertilizer, same tillage with farmland, weed control, and almost no vegetation) had a negative impact on soil microbial structural and functional diversity. Farmland with rational fertilization didnt cause the decline of soil microbial biomass and the deterioration of soil microbial structural and functional diversity. On the contrary, it had a positive effect to maintain soil microbial biomass and soil microbial structural and functional diversity.