National Institute of Oceanography and Applied Geophysics - OGS, Trieste, Italy; University of Trieste, Department of Life Sciences, Trieste, Italy.
National Institute of Oceanography and Applied Geophysics - OGS, Trieste, Italy.
Mar Environ Res. 2021 Feb;164:105245. doi: 10.1016/j.marenvres.2020.105245. Epub 2020 Dec 31.
Marine heterotrophic prokaryotes degrade, transform, and utilize half of the organic matter (OM) produced by photosynthesis, either in dissolved or particulate form. Microbial metabolic rates are affected by a plethora of different factors, spanning from environmental variables to OM composition. To tease apart the environmental drivers underlying the observed organic matter utilization rates, we analysed a 21 year-long time series from the Gulf of Trieste (NE Adriatic Sea). Heterotrophic carbon production (HCP) time series analysis highlighted a long-term structure made up by three periods of coherent observations (1999-2007; 2008-2011; 2012-2019), shared also by OM concentration time series. Temporal patterns of HCP drivers, extracted with a random forest approach, demonstrated that a period of high salinity anomalies (2002-2008) was the main driver of this structure. The reduced river runoff and the consequent depletion of river-borne inorganic nutrients induced a long-term Chl a decline (2006-2009), followed by a steady increase until 2014. HCP driving features over the three periods substantially changed in their seasonal patterns, suggesting that the years following the draught period represented a transition between two long-term regimes. Overall, temperature and particulate organic carbon concentration were the main factors driving HCP rates. The emergence of these variables highlighted the strong control exerted by the temperature-substrate co-limitation on microbial growth. Further exploration revealed that HCP rates did not follow the Arrhenius' linear response to temperature between 2008 and 2011, demonstrating that microbial growth was substrate-limited following the draught event. By teasing apart the environmental drivers of microbial growth on a long-term perspective, we demonstrated that a substantial change happened in the biogeochemistry of one of the most productive areas of the Mediterranean Sea. As planktonic microbes are the foundation of marine ecosystems, understanding their past dynamics may help to explain present and future changes.
海洋异养原核生物通过降解、转化和利用以溶解态或颗粒态形式存在的光合作用产生的一半有机物质（OM）来维持自身的生命活动。微生物的代谢速率受到大量不同因素的影响，包括环境变量和 OM 组成。为了梳理出观测到的有机物质利用速率背后的环境驱动因素，我们分析了来自的里雅斯特湾（亚得里亚海东北部）的一个长达 21 年的时间序列。异养碳生产（HCP）时间序列分析突出了一个由三个连贯观测期组成的长期结构（1999-2007 年；2008-2011 年；2012-2019 年），这与 OM 浓度时间序列一致。通过随机森林方法提取的 HCP 驱动因素的时间模式表明，一段高盐度异常时期（2002-2008 年）是这种结构的主要驱动因素。河流径流量减少以及由此导致的河流无机养分枯竭导致 Chl a 长期下降（2006-2009 年），随后直到 2014 年才稳步增加。三个时期的 HCP 驱动特征在季节模式上发生了实质性变化，表明干旱期后的年份代表了两种长期模式之间的过渡。总的来说，温度和颗粒有机碳浓度是驱动 HCP 速率的主要因素。这些变量的出现突显了温度-底物共限制对微生物生长的强烈控制。进一步的探索表明，2008 年至 2011 年间，HCP 速率没有遵循阿累尼乌斯对温度的线性响应，这表明干旱事件后微生物生长受到底物限制。通过从长期角度梳理微生物生长的环境驱动因素，我们证明了地中海最具生产力的地区之一的生物地球化学发生了重大变化。由于浮游微生物是海洋生态系统的基础，了解它们过去的动态可能有助于解释现在和未来的变化。
