Environmental Determinants of Microbial Biopolymer Degraders in Agricultural Soil

植物、真菌和节肢动物的结构性多糖、纤维素和几丁质是农业土壤有机质的主要组成部分。这些生物聚合物是与土壤氧化还原过程有关的土壤微生物群落的碳源。水非饱和土壤团聚体形成了外氧条件和内限氧条件的自然边界。这些生物地球化学界面导致氧在毫米尺度上的高度不均匀分布。在这种高度区隔的土壤中，除草剂对生物聚合物降解群落的毒性作用及其机制尚未得到解决。拟议的研究是优先计划1315“土壤生物地球化学界面”资助项目的延续。之前的项目解决了已知和新的原核生物在缺氧和缺氧条件下与纤维素降解有关的系统发育特性，并证明了酸性除草剂Bentazon和MCPA损害了纤维素降解相关的微生物过程。拟议的项目将(1)识别在缺氧和缺氧微区活跃的几丁质降解原核生物、真菌和原生生物，(2)确定各种纤维素和几丁质降解分类群对苯达松和MCPA的耐受性，(3)表征关键的几丁质降解物，(4)定量评估农业土壤生物聚合物降解过程中的氧气分布。主要方法将包括稳定同位素探测、16S rRNA、18S rRNA和几丁质酶基因分析、HPLC、GC和荧光染料分析氧传感。

The structural polysaccharides cellulose and chitin of plants, fungi, and arthropods are major components of organic matter in agricultural soils. These biopolymers are carbon sources of soil microbial communities linked to soil redox processes. Soil aggregates of waterunsaturated soil form natural boundaries of oxic conditions outside and oxygen-limited conditions inside. These biogeochemical interfaces lead to a highly heterogeneous oxygen distribution on a millimetre scale. The effects and mechanisms of the toxicity of herbicides on biopolymer degrading communities in such highly compartmentalized soils have not been resolved. The proposed study is a continuation of a project funded within Priority Program 1315 ‘Biogeochemical Interfaces in Soil’. The preceding project resolved phylogenetic identities of known and novel prokaryotes linked to cellulose degradation under both oxic and anoxic conditions, and demonstrated that the acidic herbicides Bentazon and MCPA impair microbial processes involved in cellulose degradation. The proposed project will (I) identify chitin-degrading prokaryotes, fungi, and protists that are active in oxic and anoxic microzones, (II) determine the tolerance of various cellulolytic and chitinolytic taxa to Bentazon and MCPA, (III) characterize key chitin-degraders, and (IV) will quantitatively assess oxygen distribution in during biopolymer degradation in an agricultural soil. Central methods will include stable isotope probing, analyses of 16S rRNA, 18S rRNA, and chitinase genes, HPLC, GC, and oxygen sensing via analysis of fluorescence dyes.