沉积环境中微生物及其功能对养殖活动的响应机制

An evident feature of mariculture is the deposition of large amount of organic matter (uneaten feed and fecal matters) to the benthic sediments, and results in oxygen depletion, pH decline, accumulation of nutrients and changes in redox pattern. However, unfortunately, in the most studies, it is difficult to accurately describe the spatial and temporal heterogeneity of the sediment microenvironment because of the limitation of measuring methods about some environmental factors (dissolved oxygen, pH, H2S, etc.), resulting in the vertical stratification of microbe could not be processed according to the redox pattern in the sedimentary environment, and further inaccurate results on the responding mechanism of microbe community were obtained. Our previous research had shown that the marked changes of redox status and microbial community composition in the sediment were caused by fish culture, and it was deduced that the microbial function would also be changed. However, the response of microbial community to mariculture was still unknown because of the bioturbation in the field conditions..Therefore, gradient quantity of organic matter was added into the sediment to detect the influence of fish culture on the distribution of redox bands in sedimentary environment with planar fluorescence chemical sensors. And then, the changes of microbial community structure and functions were determined. The object of this research was to reveal the response of microbial community to redox pattern caused by fish culture and provide the scientific basis for biogeochemical cycle in the farming gulf.

鱼类网箱养殖向海湾中输入的大量有机质（残饵和粪便）累积于养殖区底部并被逐级降解矿化，进而导致其沉积环境溶解氧衰竭、pH下降、营养盐累积和氧化还原格局改变。已有的研究中，传统理化指标（如溶解氧、pH、H2S等）测定方法的局限，使沉积物微环境的时空异质性难以准确刻画，导致沉积环境中微生物的垂直分层无法与氧化还原格局对应，进而对其分布及功能的影响因子研究并不精确。本项目的前期研究已经表明，长期高密度的鱼类网箱养殖已经造成养殖区沉积环境中氧化还原格局及微生物群落结构的剧烈改变，但由于现场环境生物扰动的干扰，其影响机制尚不清楚。.因此，本项目设计有机质的梯度输入量实验，采用光化学平面传感器技术定期监测沉积环境中氧化基质的分布，并结合最终微生物群落结构及其功能的变化，解晰鱼类养殖对沉积环境中氧化还原格局的影响，进而确定微生物群落及其功能对鱼类养殖活动的响应机制，为养殖海湾的生物地球化学循环研究奠定基础

鱼类网箱养殖向海湾中输入的大量有机质（残饵和粪便）累积于养殖区底部导致氧化还原格局改变，而准确精细的定量表征元素形态和分布是揭示沉积物中氧化还原格局及相关微生物参与的生物地球化学元素循环的基础。本项目通过室内培养实验，采用光化学平面传感器、高通量测序、基因芯片等技术，开展鱼类网箱养殖引起的大量有机质输入对沉积环境中氧化基质分布（形成氧化还原格局）的影响，进而引起的微生物群落结构及其功能的变化。主要研究结果包括：（1）氧化还原格局的变化。养殖活动显著改变了沉积环境的氧化还原格局，导致沉积环境中的缺氧区随着养殖强度的增加而逐渐增多，有机质的矿化路径也从以铁氧化物还原为主变为以硫酸盐还原为主。（2）细菌群落及功能对养殖强度的响应。虽然养殖活动使细菌的丰富度和多样性降低，但随着养殖强度的增加，一些特有细菌的增殖也使高养殖强度组的细菌多样性增大。养殖活动不仅改变沉积环境细菌的群落结构，使细菌间的关系更加复杂，关键种由需氧菌Gammaproteobacteria逐渐变为厌氧菌Deltaproteobacteria，也使部分参与碳降解、碳固定和氮循环的相关功能基因显著增加，显著增加的功能基因数量也随着养殖强度的增加而逐渐增多。另外，随着养殖强度的增加，PON、PO43-、H2S和POC对细菌群落分布的影响逐渐增强。而对碳循环相关基因有显著影响的环境因子包括PO43-、H2S和NH4+，对硫循环影响显著的环境因子则为NO3-+ NO2-、O2和PO43-。（3）细菌群落及功能对氧化还原格局的响应。而在不同氧化还原区中，有氧区的菌群结构及功能基因显著不同于其它2区，此区域内显著增加的OTUs 以需氧菌Gammaproteobacteria居多，且显著增加的功能基因也与碳固定和氮循环相关。氧化区与缺氧区的菌群结构及功能相似，但氧化区的菌群组内差异较大，且在此区域显著较高的OTUs多属于厌氧菌Deltaproteobacteria。研究结果为更深入研究近三十年鱼类规模化养殖迅速发展对沉积环境碳氮硫等浅海重要生源要素迁移和循环的强烈影响提供了基础数据，从而为理解和刻画人类活动对近海生态系统物质循环的影响提供重要依据。