持续干旱对樱桃根际土壤细菌数量及结构多样性影响

以1年生吉塞拉实生容器苗为试材,采用绿色荧光蛋白基因标记技术,研究了干旱胁迫(连续干旱0、7、14、21、28 d和35 d)对樱桃根际促生细菌YT3的标记菌YT3-gfp数量的影响,同时结合平板计数法和末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism,T-RFLP)技术,研究了干旱对樱桃土壤中的微生物数量及细菌群落结构多样性影响。结果表明:樱桃根际土壤中的YT3-gfp数量是非根际土壤中的8.75—28.77倍,随着持续干旱强度的增加,YT3-gfp的数量先增加后减小。干旱对根际土壤中YT3-gfp数量的影响大于对非根际土壤的影响,分别在持续干旱至第21天和28天时,YT3-gfp的数量达到最大值。随着持续干旱强度的增加,根际土壤中细菌和放线菌数量先增加后减小,而真菌的数量一直减少。此外,持续干旱至第21天或28天时,樱桃根际土壤具有最高的丰富度指数、多样性指数和最低的优势度指数。基于T-RFLP的主成分分析结果显示持续干旱14—35 d时,其细菌群落结构成为一个相对独立的群,群落结构趋于多样性;而持续干旱7 d和42 d构成另外两个相对独立的群,群落结构趋于简单。以上分析可知,干旱对土壤微生物影响显著,一定强度的干旱可提高细菌和放线菌数量,提高细菌群落结构多样性,适当干旱对维持根际土壤细菌群落结构多样性是有益的。

Effects of continuous drought on soil bacteria populations and community diversity in sweet cherry rhizosphere

Drought stress in soil can be crucial to plant yield because it reduces growth rate, stem elongation, leaf expansion, and stomatal movements. Several microorganisms in the rhizosphere soil are free-living, soil-borne bacteria that aggressively colonize the rhizosphere or plant roots. The efficiency of rhizosphere microorganisms in promoting plant growth has been demonstrated in numerous greenhouse and field studies on different plant species. However, studies on the influences of continuous drought on rhizosphere microbial populations and community diversity are limited. Therefore, a bacterial strain with known positive effects on plant growth, named YT3, was used in the present study to investigate the effect of continuous drought on soil bacteria population. The bacterial strain was isolated and screened using the serial dilution method on the rhizosphere soil of sweet cherry (Cerasus pseudocerasus) growing fields. YT3-gfp was labeled with green fluorescent protein into plant growth-promoting rhizobacteria YT3. A pot experiment was conducted to determine whether continuous drought stress (continuous drought of 7, 14, 21, 28, 35, and 42 d) could benefit YT3-gfp activities in sweet cherry rhizosphere soil. In addition, the effect of continuous drought stress on microbial populations, as well as the community diversity in rhizosphere soil was investigated by plate culture method and terminal restriction fragment length polymorphism (T-RFLP) analysis. The results showed that the YT3-gfp populations in the rhizosphere soil were 8.75 to 28.77 times higher than those in the non-rhizosphere soil of sweet cherry. The YT3-gfp amount increased simultaneously with the continuous drought stress in rhizosphere soil or non-rhizosphere soil; however, a decrease was also observed during the severe drought stress period. YT3-gfp in the rhizosphere was more easily subjected to drought stress than that in non-rhizosphere soil. The maximum YT3-gfp amounts in rhizosphere soil and non-rhizosphere soil were observed on day 21 at 166 × 10⁴ CFU/g and on day 28 at 6.7 × 10⁴ CFU/g. Along with continuous drought stress, bacteria and actinomycete populations, as well as the total microorganism amounts, first increased then decreased; however, fungus populations in the rhizosphere soil of sweet cherry decreased continuously. Continuous drought stress significantly influenced the T-RFLP profiles in the rhizosphere soils of sweet cherry seedlings. The T-RFLP profiles showed that some special terminal restriction fragments (T-RFs) decreased, and some T-RFs disappeared with continuous drought stress. However, some T-RFs appeared under certain drought stress conditions. The highest Margalef and Shannon indexes and the lowest Simpson's index were observed on days 21 or 28 after continuous drought stress. Moreover, the principal component analysis for T-RFs of the different treatments showed that an independent group of bacterial community structure was formed during continuous drought stress in 14 days to 35 days, indicative of the diversiform community structure. The other two independent groups were formed on days 7 and 42 after continuous drought, respectively, indicative of the simplified community structure. Consequently, soil bacteria community structure was significantly influenced by continuous drought stress. Certain drought stress can improve the bacteria and actinomycete populations, and increase the microbial community diversity. Therefore, certain drought stress is beneficial to the sustainable microbial community structure in sweet cherry rhizosphere soil.