[Effects of tillage managements on soil microbial community structure in soil aggregates of fluvo-aquic soil]

In order to explore the impacts of different tillage managements on the structure and diversity of microbial community in fluvo-aquic soil, the phospholipid fatty acid (PLFA) method was used to determine microbial community composition in soil aggregates. Four tillage treatments were set up in Qihe County, Shandong Province, including rotary tillage with straw return (RT), deep ploughing with straw return (DP), subsoiling with straw return (SS) and no-tillage with straw return (NT). Our results showed that DP treatment significantly increased the amount of fungal PLFAs and fungi/bacteria ratio in >5 mm soil aggregates compared with RT. DP could provide favorable conditions for fungi reproduction, facilitate soil organic matter storage and soil buffering capacity. DP increased the amount of PLFAs in 5-2 mm soil aggregates, reduced the gram-positive (G+) /gram-negative (G-) bacteria ratio in the soil, and improved soil nutritional status. In addition, DP improved the microbial abundance index in <0.25 mm soil aggregates. In general, DP could not only increase the abundance of bacteria and fungi in soil aggregates, but also improve the microbial community structure of soil aggregate, which help increase soil carbon sequestration capacity and keep soil microbial diversity to a certain extent. Results of the redundancy analysis showed that the total PLFAs, PLFAs of bacteria, G- bacteria and actinomycetes in soil aggregates are closely correlated with soil organic carbon, while PLFAs of G+ bacteria had a strong correlation with soil total nitrogen concentration. In each treatment, microbial communities in larger sizes of soil aggregates were mainly affected by the ratio of organic carbon to total nitrogen, soil moisture, pH, and mass fractions of soil aggregates, while the microbial communities in smaller sizes of soil aggregates were affected by the concentrations of organic carbon and total nitrogen.