连作对芝麻根际土壤微生物群落的影响

采用稀释平板计数法研究了不同连作年限处理芝麻根际土壤细菌、真菌、放线菌、芽孢杆菌、尖孢镰刀菌(FO)和青枯劳尔氏菌(RS)数量的变化情况。结果表明,随着连作年限的增加,芝麻根际土壤中细菌和放线菌的数量下降,而真菌的数量则呈上升趋势。新种芝麻地根际土壤芽孢杆菌数量显著高于连作2a处理和连作5a处理,而连作2a处理又显著高于连作5a处理;连作5a芝麻根际土壤尖孢镰刀菌数量显著高于新种地、轮作1a和连作2a等3个处理;轮作1a、连作2a及连作5a等3个处理青枯劳尔氏菌数量显著高于新种地处理。说明连作导致土壤微生物环境恶化,引起根际微生物区系结构发生定向改变。连作2a与轮作1a相比,各菌群(类群)数量差异均不显著。

Effect of continuous cropping of sesame on rhizospheric microbial communities

China is one of four main sesame producing countries in the world, with approximately 600000 hectares planted annually. When sesame is grown continuously in the same field over several years, yield is reduced due to declining soil health. This phenomenon is called the continuous cropping obstacle. In 2010, the area of continuous cropping of sesame was over 1500 hectares in Jiangxi Province alone. The latest hypothesis for the decline in soil health focuses on shifts in the soil microbial community under continuous cropping. Bacteria, fungi, and actinomycetes are the three main microbial groups in the soil. Their variation in abundance and diversity reflect the level of biological activity in the soil. Soil with abundant bacteria and actinomycetes is more biologically active. When the fungal abundance of soil increases, this usually means a decrease in soil fertility. Bacillus bacteria have vital functions in soil improvement and pest control. Sesame wilt caused by Fusarium oxysporum (FO), and sesame bacterial wilt caused by Ralstonia solanacearum (RS), are serious diseases. We examined changes in abundance of bacteria, actinomycetes, fungi, Bacillus, Fusarium oxysporum, and Ralstonia solanacearum, in sesame rhizospheric soil under four treatments; using dilution plate counting to investigate effects of continuous cropping on the microbes present. The four treatments were: normal rotation with vegetable crop (vegetable-vegetable-vegetable-sesame, VVVS), alternation of sesame with peanut (sesame-peanut-sesame, SPS), 2 year continuous sesame (CS2), and 5 year continuous sesame (CS5). Bacteria, actinomycetes, and Bacillus, decreased in abundance, while fungi, Fusarium oxysporum, and Ralstonia solanacearum increased in abundance, with increasing length of continuous cropping. Bacterial abundance under VVVS, SPS, and CS2 was significantly higher than under CS5, and bacterial abundance under VVVS was significantly higher than under CS2. Actinomycete abundance under VVVS, SPS, and CS2 was significantly higher than under CS5. Fungal abundance under CS5 was significantly higher than under VVVS, SPS or CS2, and fungal abundance under CS2 was significantly higher than under VVVS. Bacillus abundance under VVVS was significantly higher than under CS2 or CS5, and Bacillus abundance was significantly higher under CS2 than under CS5. Fusarium oxysporum abundance under CS5 was significantly higher than under VVVS, SPS or CS2. Ralstonia solanacearum abundance under SPS, CS2 and CS5 was significantly higher than under VVVS. There were no significant differences in the abundance of bacteria, actinomycetes, fungi, Bacillus, Fusarium oxysporum, or Ralstonia solanacearum between SPS and CS2. It was clear that continuous cropping of sesame led to direct changes in the microbial composition of the rhizosphere. Bacteria and actinomycetes decreased in abundance, while fungi increased. When rhizospheric soil changes from "bacterial" to "fungal", its biological activity and fertility decline, and it is slower to recover from ecological fluctuations caused by external factors such as pathogens and waterlogging. Fusarium oxysporum and Ralstonia solanacearum continue to increase in abundance, causing worsening diseases. These factors eventually lead to continuous cultivation problems in sesame.