Microbial and geochemical mechanisms controlling dissolution processes of particulate organic matter in the oceans

微生物在调节海洋物质循环中起着主要作用，但由细菌介导的物质通量的控制机制尚未完全阐明。特别是我们对海洋水体中有机物-细菌相互作用的大规模模式和控制的了解有限。为了更好地了解大尺度海洋生物地球化学循环的动态特征，本研究考察了南太平洋和北太平洋表层和深层水体中微生物分布和有机质转化分解的模式。我们的数据显示，细菌生产在很大程度上与中上层（100 - 1000 m）下沉的颗粒有机碳通量相耦合，支持了颗粒有机碳->溶解有机碳->自由生活原核生物途径在生物泵调节中起重要作用的假设。然而，颗粒有机碳沉降通量与原核生物活性之间的耦合在深海层（bbb10,000 m）中较弱，表明沉积物中有机质的侧向输送或再悬浮在该层中很重要。我们还研究了藻华期间细菌群落和微生物活动的动态。根据中观实验结果，我们得出结论，与细胞噬菌-黄杆菌群相关的丝状细菌在水华过程中对颗粒有机物的分解起重要作用。最后，我们建立了一个新的数学模型来研究海洋中颗粒和溶解有机物分解过程中细菌群落的动态行为。上述研究共同揭示了海洋中有机物-微生物相互作用的新特征。

Microbes play the major role in the regulation of material cycling in the oceans, but the mechanisms by which material fluxes mediated by bacteria are controlled have yet to be clarified fully. Especially our knowledge is limited regarding large scale patterns and controls of organic matter - bacteria interactions in oceanic water columns. In order to better understand dynamic features of the oceanic biogeochemical cycles at a large scale, this study examined patters in distributions of microbes and organic matter transformations and decomposition in the surface and deep water columns of the South and North Pacific. Our data revealed that bacterial production is largely coupled with the flux of sinking particulate organic carbon in the mesopelagic zone (100 - 1,000 m), supporting the hypothesis that particulate organic carbon -> dissolved organic carbon -> free-living prokaryote pathway is important in the regulation of the biological pump. However the coupling between the sinking fluxes of particulate organic carbon and prokaryotic activity was weak in the bathypelagic layer (>1,000 m), suggesting that the lateral transport or resuspension of organic matter from the sediment is important in that layer. We also investigated the dynamics of bacterial communities and microbial activities during the algal blooms. On the basis of the results obtained by mesocosm experiments, we concluded that filamentous bacteria affiliated with the Cytophaga-Flavobacter cluster play an important role in particulate organic matter decomposition during the bloom. Finally, we constructed a new mathematical model to examine dynamic behavior of bacterial communities during the decomposition of particulate and dissolved organic matter in the oceans. The above studies collectively revealed novel features in the organic matter- microbe interactions in the oceans.