棉秆促腐还田化感作用及棉花根际微生态效应研究

Xinjiang province is the largest cotton planting area in China, the cultivation area and yield of cotton rank first in the nationwide. Long-term continuous cropping and unique production technology of returning cotton stalk to field have formed due to special geographical environment,which have led to increasingly serious continuous cropping obstacles. It has been proved that the autotoxicity resulting from straw returning to field is one of the most important reason for continuous cropping obstacles. Our group has decayed cotton stalk by using the complex of lignocellulose decomposing strains previously isolated, found that the microbial decaying way could effectively eliminate the autotoxicity of cotton stalk decomposed residues to cotton growth, reduce potential content of allelochemicals, and effectively inhibit colonization of Fusarium and Verticillium wilts. Therefore, this research plans to furtherly validate and expand the applicability of promoted-decaying cotton stalk returning to field. The type of decaying microbial inoculum, strain preparing form and application way will be determined through pot experiments on the basis of existing strains, the allelopathy on cotton growth and the infectious status of Fusarium and Verticillium wilts will be analyzed after applying decaying microbial inoculums in field experiments,the differences of allelochemicals in rhizospere soils will be examined, the bioassay will be developed to examine allelopathy of main different chemicals; and the physiochemical properties of rhizospere soils, soil enzyme activity and dynamic variation of rhizosphere microflora will be measured, with expectation to reveal the dynamic variation of allelopathy of promoted-decaying cotton stalk returning to continuous cropping cotton field and response mechanism of cotton rhizosphere microecology, and provide helpful theoretical basis for reasonable way of cotton stalk returning to field.

新疆棉花种植面积与产量居全国第一，因环境条件特殊，形成了棉花长期连作并实施棉秆还田的独特生产技术体系，导致连作障碍现象日益严重。研究证实，秸秆还田的自毒化感效应是导致作物连作障碍的重要原因之一。项目组前期研究以筛选到的复合菌剂人工腐解棉秆，发现可有效消除棉秆腐解物对棉花的自毒作用，降低潜在化感物质含量，并对棉花枯黄萎病菌具有较好抑菌效果。基于此，本研究拟进一步验证和拓展棉秆促腐还田的适用性，在已有菌种基础上，通过盆栽实验确定腐解菌种类、剂型及施入方式，然后开展田间试验分析施入腐解菌剂后对棉花生长的化感效应及枯黄萎病发病情况；比较根际土壤中潜在化感物质的差异及含量变化，并对其中主要差异成分进行化感作用生物测定；监测根际土壤理化性状、土壤酶活及根际微生物群落动态变化，以期揭示出连作棉田棉秆促腐还田化感作用规律及棉花根际微生态的响应机制，从而为最终建立合理的棉秆还田方式奠定有益的理论基础。

本研究针对新疆棉田长期连作及实施棉秆还田的耕作模式所出现的连作障碍问题，通过筛选制备棉秆促腐菌剂，探讨棉秆促腐还田对棉花生长的化感作用以及对棉花根际微生态环境的影响。研究发现：（1）筛选获得发酵液及棉秆腐解液对棉花生长无不利影响的复合菌剂；（2）对菌剂进行包埋或吸附固定，可提升菌剂的作用效果，使棉花幼苗维持健康的生理状态。其中菌剂的施用量尤为关键，菌剂量过高反而会影响到应用效果，甚至造成化感物质得不到有效降解、棉花幼苗生长受到抑制等。（3）盆栽实验证实，施用促腐菌剂可有效降低棉秆腐解的自毒作用，腐解过程中产生的邻苯二甲酸二丁酯（DBP）、邻苯二甲酸二异丁酯（DIBP）等主要化感物质显著降低，从而为棉花生长维持较好的生长环境。但随着棉秆还田量的增加，促腐菌剂的作用效果逐渐降低。（4）小区实验显示，施用促腐菌剂后，土壤中DBP、DIBP等化感物质有效降低。菌剂对土壤转化酶活性影响较小，对土壤中N、P、K等养分没有显著不利影响，甚至土壤蔗糖酶、脲酶有一定提升；在蕾期以前，可一定程度增加土壤P、K元素含量。本研究所用促腐菌均为真菌，施菌处理土壤中的细菌群落多样性要低于对照处理，说明促腐菌与土壤中细菌的竞争值得深入关注。以上研究成果，可为最终建立合理的棉秆促腐还田方式奠定有益的理论基础。此外，在项目执行中针对较为普遍的作物-棉花套作体系也开展了相关研究，发现不同作物与棉花间也可能产生化感作用。一定浓度核桃叶水浸提液将对棉花种子萌发和幼苗生长产生抑制，而苹果、香梨、茴香3种作物与棉花套作，土壤中的一些转化酶有较大程度提高，硝态氮，氨态氮和无机磷等也有一定提升，茴香-棉花套作土壤中固氮菌、纤维素分解菌的数量在花蕾期和吐絮期相比其余土壤有显著增加。研究结果可为选择合适的作物与棉花套作提供一定参考。