Abstract
Fertilizer applications have important effects on soil microbial abundance and community structure. In this study, total soil microbial DNA and RNA were directly extracted from paddy soils of N0 (control treatment, no nitrogen fertilizer), NPK (balanced fertilization), NPK+LS (balanced fertilization with additional 3.0 t·hm-2 rice straw incorporation) and NPK+HS (balanced fertilization with additional 6.0 t·hm-2 rice straw incorporation) treatments in a long-term fertilization experiment of double rice cropping system in Changsha County, Hunan Province. Soil bacteria community structures were evaluated by analyzing the 16S rRNA gene fragments at DNA and cDNA levels with Terminal Restriction Fragment Length Polymorphism (T-RFLP) and quantitative PCR techniques. Balancing fertilization with chemical fertilizers and rice straw incorporation significantly changed the composition of bulk (DNA-based) and potentially active (mRNA-based) soil bacterial community as shown in T-RFLP profiles, and also reduced the bulk soil microbial diversity, but not the potentially active ones, as compared with the control treatment. The DNA-based abundance of 16S rRNA gene was on average 377 times as many as the m-RNA based population size. Compared to N0,balanced fertilization with rice straw incorporation (NPK+LS and NPK+HS) increased the bulk and active copy numbers of 16S rRNA gene, but not for balanced fertilization (NPK). The abundance and microbial community structure were not significantly different between the NPK+LS and NPK+HS treatments. Redundancy analysis (RDA) showed that soil ammonium was the key environmental factor determining the bulk and active soil microbial community structure among the treatments. In conclusion, the effect of fertilization on soil microbial abundance and community structure could be indicated at both DNA and cDNA levels; the cDNA information could better reflect the adaptability of bacterial community to the environmental stress.
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