腐殖质呼吸作用及其生态学意义

Humus respiration and its ecological significance

腐殖质呼吸是厌氧环境中普遍存在的一种微生物呼吸代谢模式。自1996年发现以来,日益成为生态学与环境科学领域的研究热点。在厌氧条件下,一些微生物能以腐殖质作为唯一电子受体,氧化环境中的有机质或者甲苯等环境有毒物质,产生CO2,参与碳循环;同时,腐殖质呼吸作用产生的还原态腐殖质可以还原环境中的一些氧化态物质,如Fe(III)、Mn(IV)、Cr(VI)、U(VI)、硝基芳香化合物和多卤代污染物。因此,腐殖质呼吸能够影响环境中C、N、Fe、Mn以及一些痕量金属元素的生物地球化学循环,并且能够促进重金属以及有机污染物的脱毒,在水体自净、污染土壤原位修复、污水处理等方面具有积极作用。

Humus is a ubiquitous component in the environment and can be readily isolated from nearly all soils, waters, and sediments. Humus biodegrades poorly and is formed from the decomposition of plant, animal, and microbial cells in soils and sediments. The functional groups of humus, which determine the physical and chemical characteristics, vary depending on the origin and age of the material. An in-depth understanding of the reaction chemistry of humus and the role played by these compounds in geochemical cycles has been a major scientific focus for over a century. However, the interactions between these compounds and microbial populations have only recently gained scientific attention. It is now known that humic substances may play an important role in the anaerobic biodegradation and biotransformation of organic as well as inorganic compounds. Humus can be utilized by microorganisms as effective electron acceptors for the oxidative degradation of organic carbon in anaerobic environments. Alternatively, reduced humic substances can be utilized by microorganisms as electron donors for the assimilation of organic carbon coupled to denitrification. Microbially reduced humus can act as soluble electron carriers between microorganisms and metal oxides such as Fe （III） oxides, allowing for the regeneration of humus to the oxidized form. Thus, even sub-stoichiometric concentrations of humus can mediate both anaerobic substrate oxidation and metal oxide reduction. Additionally, humus can serve as electron shuttles, abiotically transferring electrons from an external electron donor to priority pollutants, which are susceptible to reductive transformations （e. g., nitroaromatics, azo dyes and polyhalogenated compounds ）. These interactions may have a significant impact on the fate and transport of organic and inorganic environmental pollutants. An understanding of these interactions may improve strategies for bioremediation of particular pollutants. Likewise, predicting the behavior and longevity of pollutants within the environment may be better modeled, resulting in improved design strategies for bioremediative processes. This paper presented a review on humus respiration which has only recently been recognized as a novel respiratory pathway for a diverse community of humus-reducing microorganisms. Likewise, the role of humic substances on the degradation of priority pollutants was discussed in this paper.