Oxygen (O2) deficiency and nutrient concentrations in marine systems are impacting organisms from microbes to higher trophic levels. In coastal and enclosed seas, O2 deficiency is often related to eutrophication and high degradation rates of organic matter. To investigate the impact of O2 concentration on bacterial growth and the turnover of organic matter, we conducted multifactorial batch experiments with natural microbial communities of the central Baltic Sea. Water was collected from suboxic (<5 μmol l−1) depths in the Gotland Basin during June 2015. Samples were kept for 4 d under fully oxygenated and low O2 conditions (mean: 34 μmol l−1 O2), with or without nutrient (ammonium, phosphate and nitrate) and labile carbon (glucose) amendments. We measured bacterial abundance, bacterial heterotrophic production, extracellular enzyme rates (leucine-aminopeptidase) and changes in dissolved and particulate organic carbon concentrations. Our results show that the bacterial turnover of organic matter was limited by nutrients under both oxic and low O2 conditions. In nutrientand glucose-replete treatments, low O2 concentrations significantly reduced the net uptake of dissolved organic carbon and led to greater accumulation of more labile dissolved organic matter. Our results therewith suggest that the combined effects of eutrophication and deoxygenation on heterotrophic bacterial activity might favor the accumulation of dissolved organic carbon in the Baltic Sea.

中文翻译：

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氧气和无机养分对波罗的海微生物碳周转的潜在作用

海洋系统中的氧气 (O2) 缺乏和营养浓度正在影响从微生物到更高营养级别的生物。在沿海和封闭海域，O2 缺乏通常与富营养化和有机物的高降解率有关。为了研究 O2 浓度对细菌生长和有机物周转的影响，我们对波罗的海中部的天然微生物群落进行了多因素批量实验。2015 年 6 月，从哥特兰盆地的低氧 (<5 μmol l-1) 深度收集水。样品在全氧和低 O2 条件下保存 4 天（平均值：34 μmol l-1 O2），有或没有营养（铵、磷酸盐和硝酸盐）和不稳定碳（葡萄糖）修正物。我们测量了细菌丰度、细菌异养生产、细胞外酶速率（亮氨酸-氨肽酶）以及溶解和颗粒有机碳浓度的变化。我们的结果表明，在有氧和低 O2 条件下，有机物的细菌周转受到营养物质的限制。在营养和葡萄糖充足的处理中，低 O2 浓度显着降低了溶解有机碳的净吸收，并导致更不稳定的溶解有机物质的更大积累。我们的结果表明，富营养化和脱氧对异养细菌活动的综合影响可能有利于波罗的海溶解有机碳的积累。我们的结果表明，在有氧和低 O2 条件下，有机物的细菌周转受到营养物质的限制。在营养和葡萄糖充足的处理中，低 O2 浓度显着降低了溶解有机碳的净吸收，并导致更不稳定的溶解有机物质的更大积累。我们的结果表明，富营养化和脱氧对异养细菌活动的综合影响可能有利于波罗的海溶解有机碳的积累。我们的结果表明，在有氧和低 O2 条件下，有机物的细菌周转受到营养物质的限制。在营养和葡萄糖充足的处理中，低 O2 浓度显着降低了溶解有机碳的净吸收，并导致更不稳定的溶解有机物质的更大积累。我们的结果表明，富营养化和脱氧对异养细菌活动的综合影响可能有利于波罗的海溶解有机碳的积累。