降解玉米秸秆真菌复合菌系的构建及其降解效果评价

  【目的】  秸秆的木质纤维素含量丰富、结构复杂，在自然界中降解较慢，增加秸秆降解菌剂中菌株的多样性有利于提升还田秸秆的降解效果。探究菌株多样性水平和组成影响复合菌系秸秆降解的效果及原因，为复合菌系在秸秆降解中的应用提供理论支撑。  【方法】  通过富集驯化培养，从玉米秸秆还田土壤中筛选具有秸秆降解能力的真菌，从中挑选5株高效秸秆降解真菌进行基因间隔区序列 (ITS) 测定和物种鉴定，明确其分类地位。通过全组合构建菌株多样性为1～5的复合菌系，分别检测复合菌系的秸秆相对降解率及其滤纸酶、纤维素内切酶和木聚糖酶活性，利用方差分析和相关性分析等方法研究菌株多样性和组成对复合菌系玉米秸秆降解效果及其纤维素酶活性的影响。  【结果】  共筛选获得了15株具有秸秆降解能力的真菌，其中5株真菌的秸秆降解效果好、纤维素水解能力强。经ITS序列鉴定和系统发育分析，发现5株降解真菌的遗传差异较大，Z7-6、F7-5、F4-3、L1-1和J2-5分别与草酸青霉 (Z7-6: Penicillium oxalicum)、烟曲霉 (F7-5: Aspergillus fumigatus)、哈茨木霉 (F4-3: Trichoderma harzianum)、白囊耙齿菌 (L1-1: Irpex lacteus) 和木贼镰刀菌 (J2-5: Fusarium equiseti) 的ITS序列相似度均超过99.95%。全组合复配结果表明，复合菌系的秸秆降解能力和纤维素酶活力均高于各单一菌株，且随着菌株多样性水平的增加而提高。滤纸酶、纤维素内切酶和木聚糖酶的活力越强，复合菌系对玉米秸秆的降解效果越好，而其秸秆相对降解率主要取决于滤纸酶和纤维素内切酶的活性。抽样效应分析发现，不同菌株对复合菌系的秸秆降解效果、滤纸酶和纤维素内切酶活性的影响不同。不含菌株F7-5的复合菌系降解效果显著优于含有该菌株的组合，以Z7-6 (P. oxalicum)、F4-3 (T. harzianum)、L1-1 (I. lacteus) 和J2-5 (F. equiseti) 组合F1的玉米秸秆降解效果最佳、酶活性最高。  【结论】  秸秆降解复合菌系的构建过程需要同时考虑多样性效应和抽样效应，增加降解菌的多样性有助于增强秸秆的降解效果。本研究筛选获得的复合菌系F1在玉米秸秆降解中具有潜在的应用前景。

Construction and evaluation of fungal consortia effect on maize straw degradation

【Objectives】The degradation of straw is relatively slow in nature due to its high content of complex celluloses.Increase in the degrading agents such as microbes and enzymatic activities may improve the degradation of straw.Thus,we studied the influence of microbial diversity and composition on maize straw degradation.【Methods】Straw degrading fungi were isolated from the soil of maize straw field.Five fungi strains with high degradation ability were classified into microbial consortia through internal transcribed spacer(ITS)identification.The strain richness of the microbial consortia was set from 1 to 5 based on the degrading fungi.The relative degradation efficiency of maize straw and the activities of filter paper enzyme(FPe),CMCase and xylanase in different microbial consortia were assessed via variance and correlation analyses.【Results】The five selected strains with high degradation efficiency were identified as Penicillium oxalicum Z7-6,Aspergillus fumigatus F7-5,Trichoderma harzianum F4-3,Irpex lacteus L1-1 and Fusarium equiseti J2-5 based on ITS alignment and phylogenic analysis.Relative straw degradation efficiency and cellulase activities of the fungal consortia were higher than single strains,and they increased with the enhancement of species richness in the fungal consortia.The consortia with strong activities of(FPe),CMCase and xylanase degraded maize straw more than others.FPe and CMCase strongly associated and contributed to relative degradation efficiency of the microbial consortia.Sampling effect analysis showed that different strains had different effects on maize straw degradation and cellulase activities.The maize straw degradation under all consortia without F7-5 strain was significantly higher than that with F7-5 strain.The fungal consortia of P.oxalicum Z7-6,T.harzianum F4-3,I.lacteus L1-1 and F.equiseti J2-5 showed the highest relative degradation efficiency and cellulase activities.【Conclusions】Increasing the diversity of microbial consortia could enhance maize straw degradation;however,diversity and sampling effects should be considered during microbial composite construction.