促分解菌剂对还田玉米秸秆的分解效果及土壤微生物的影响

为了探明促分解菌剂的应用对还田玉米秸秆的促分解效果及对土壤微生物群落结构的影响,选用3组促分解菌剂,编号依次为ND、NK和NS,于2009年10月至2010年4月期间,在河北省农林科学院辛集实验站冬小麦-玉米轮作田对玉米秸秆还田地进行了接种试验。在接种后的15、25、145和160 d分别测定秸秆残重率和秸秆残渣中C/N,结果表明与未施菌剂对照(CK)相比,3组菌剂均在一定程度上加快了玉米秸秆的分解,其中以菌剂ND促分解效果最好,NK次之,NS较差,三者的最高促分解效果分别比CK提高了14.3%、7.7%和1.6%,主要促分解效果都出现在早期(前25 d),且菌剂促进秸秆残渣中C/N降低的效果也在早期明显。采用变性梯度凝胶电泳技术(DGGE)检测菌剂对玉米秸秆降解过程中土壤细菌和真菌群落结构的影响,结果表明,与不接种CK相比,接种菌剂主要在早期对土壤细菌和真菌的群落结构产生较大的影响,而后期对土壤微生物群的影响不明显。秸秆还田后接种促分解菌剂,能在接种早期有效加快秸秆分解,而随接种后时间的推进,其促进效果逐渐减弱,与之对应,土壤微生物群落结构早期差异明显,其后差异逐渐减小。

Effects of microbial inoculants on soil microbial diversity and degrading process of corn straw returned to field

Returning crop straw to field is one of the common methods to improve soil organic matter and achieve sustainable development of agriculture. However, corn straw is composed mainly of highly polymerized lignocellulose with a high carbon to nitrogen (C:N) ratios, and it degrades slowly in the field. The difficulty of straw degradation in a short time hampers the seedling growth and farming operation. In some place farmers burn crop straw after harvest in order to immediately sow the next crop, which contributes to environmental pollution and greenhouse gas emissions. Acceleration of straw degradation in the field is urgently needed, and utilization of microbial inoculants is a safe and effective method. To reveal the effects of microbial inoculants on degrading process of corn straw and soil microbial diversity after straw was returned to the field, an incubation experiment was carried out in the field. The experiment was conducted in the winter Wheat - maize rotation of the high yield area located around Hebei Academy of Agriculture and forestry Sciences, North China Plain from Oct 2009 to Apr 2010, and three different microbial inoculants (ND, NK and NS) were used in this study. The residual weights and C/N ratios of corn straw in different inoculated treatments were measured to estimate the degrading enhancement of the three inoculants at four different sampling times of 15d, 25d, 145d and 160d. The results showed that the degradation of corn straw could be enhanced by inoculation in early period (first 25d), and residual percentages of corn straw in ND, NK and NS were 14.3%, 7.7% and 1.6% lower than that in CK, respectively. C/N ratios of corn straw in inoculant treatments decreased more rapidly than that in CK, and the decreases were also showed up in early stage. In order to find the effects of microbial inoculants on soil microbial diversity, V3 region of bacterial 16S rDNA and D1 region of fungal 26S rDNA gene sequences were detected by denaturing gradient gel electrophoresis (DGGE), and Cluster analyses based on the band similarity in migration and intensity between lanes were used to understand the distance of each lanes . Furthermore bands of the three inoculants were used to study the relationships between inoculation and soil microbial diversity, and dominant bands of bacteria and fungi were excised from DGGE gels and sequenced to get further microbial information. The results showed that most bands from inoculants, which matched to Bacillus fusiformis (97%), Chloroflexus bacterium (87%), Uncultured Clostridiales bacterium (99%) and Uncultured compost bacterium (92%) were detected in early stage and disappear in later stage, and some band from inoculants were not detected. Soil bacterial and fungal composition responded to each added microbial inoculants in early stage. Compared with CK, adding microbial inoculants after straw returning to the field could effectively accelerate corn straw degradation in early period, and soil microbial diversity was accordingly different in early period and gradually went to the same level in late stage of the inoculation.