| Soil microorganisms are major participant in many soil ecological processes, such as governing the organic matter decomposition and nutrient cycling. Meanwhile, soil microorganisms are sensitive to the changes of soil environment. Changes in soil physiochemical properties would induce a rapid response in soil microbial biomass, activity and community structure. Hence, the changes in soil microbial properties were often used as an effective index of measuring the soil quality. The present study was conducted based on in a long-term tillage trial in black soil, in Northeast Institute of Geography and Agroecology, ChineseAcademy of Sciences, in Dehui County, Jilin Province, China. Field experiment, lab analysis and field in-situ incubation with stable isotope method were conducted to study. 1) the effects of sampling time, tillage managements and crop rotation on soil organic carbon fraction, soil physical properties and microbial properties and 2) the relationship between soil physichemical properties and microbial properties.We also analyzed the response of soil microbial community to residue managements and contents of new carbon flowing into different microbial communities in no tillage and moldboard plough. The present study is helpful for revealing the impacting mechanism of soil microorganism on C turnover in black soils.We obtained the following results:(1) Conservation tillage significantly increased soil organic carbon(SOC) content in surface soil(0-5 cm). The SOC in no tillage(NT) was 8.3 % and 28.2 % higher, respectively, than ridge tillage(RT) and mouldboard plow(MP) in 0-5 cm depth soil. However, the SOC was higher in MP and RT than in NT in 5-10 depth soil. This suggested that NT has the potential to accumulate carbon in surface 5 cm soil, and cause a decrease in sub-surface(<5 cm) soil.(2) Long-term conservation tillage significantly increased the soil microbial biomass carbon(MBC) content in surface soil(0-5 cm).(3) The temporal variation of MBC in conservation tillage was distinct from that in conventional tillage. The highest MBC content generally occured in August in NT and RT, while in June in MP.(4) Principal response curve(PRC) analysis revealed the magnitude of the effect of sampling date on the PLFA relative abundance decreasedwith depth within the tilled layer, whereas increased with depth for tillage practice. NT and RT imcreased microbial abundance(total, fungal and bacterial abundance) in the 0-5 cm depth soil, but they did not contribute to a higher F/B ratio in the 0-5 cm depth soil, and even contributed a lower F/B ratio than MP in soils below 5 cm depth. These results demonstrated that long-termconservation tillage practice has the potential to improve microbial properties in surface soil, but do not have to cause a shift of microbial community structure in black soils.(5) Soil microbial metabolism ability was significantly affected by both tillage management and crop rotation, with crop rotation had the dominant influence. Amines/amides and amino acids which contain nitrogen in chemical formula are the main sensitivecarbon source in maize-soybean rotation, while carbohydrates are the main sensitive carbon source inmonoculture maize management. No tillage and maize-soybean rotation improved surface(0-5 cm) soil microbial metabolism activity, substrate richness and evenness, which revealed that no tillage combined with crop rotation could improve soil biological quality and make agricultural systemsmore sustainable.(6) In the present study, soil water content and temperature had no significant effect on microbial community structure. The variation of soil pore distribution might be one of the major factors inducing the changes of microbial community. NT promoted the formation of large macropores in 0-5 cm depth soil. The large macropores had highly significantly positive relationship with the relative abundance of saprophytic fungi, and bacteria had positive relationship with both large macropores and micropores.(7) The in-situ incubation of maize residue revealed that the microbial abundance increased with time in NT, and the highest microbial abundance occurred in the second stage of incubation in MP. Compared with MP, NT increased the microbial abundance in surface soil(0-5 cm) and promoted the fungal dominant role in microbial community.(8) The accumulation time of 13 C in fungi was longer than in bacteria in NT; the content of 13 C in fungi, actinomycetes and gram negative bacteria in NT was significantly higher in NT than in MP, on the contraty, it is higher in MP than in NT for bacteria and gram positive bacteria.In conclusion, conservation tillage practice has potential for increasing organic carbon in surface soil and enhancing microbial metabolic activity. Meanwhile, it drives changes in microbial community structure, which is benefitial for soil microbial accumulation. Hence, conservation tillage is an effective strategy for the sustability of agricultural system. |
PDF Full Text Request