Université de Toulouse, UPS, INP, EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement), 118 route de Narbonne, F-31062 Toulouse, France; CNRS, EcoLab, F-31062 Toulouse, France.
Sci Total Environ. 2014 Jan 1;466-467:856-63. doi: 10.1016/j.scitotenv.2013.07.121. Epub 2013 Aug 25.
Microbial denitrification is the main nitrogen removing process in freshwater ecosystems. The aim of this study was to show whether and how water warming (+2.5 °C) drives bacterial diversity and structuring and how bacterial diversity affects denitrification enzymatic activity in phototrophic river biofilms (PRB). We used water warming associated to the immediate thermal release of a nuclear power plant cooling circuit to produce natural PRB assemblages on glass slides while testing 2 temperatures (mean temperature of 17 °C versus 19.5 °C). PRB were sampled at 2 sampling times during PRB accretion (6 and 21days) in both temperatures. Bacterial community composition was assessed using ARISA. Denitrifier community abundance and denitrification gene mRNA levels were estimated by q-PCR and qRT-PCR, respectively, of 5 genes encoding catalytic subunits of the denitrification key enzymes. Denitrification enzyme activity (DEA) was measured by the acetylene-block assay at 20 °C. A mean water warming of 2.5 °C was sufficient to produce contrasted total bacterial and denitrifier communities and, therefore, to affect DEA. Indirect temperature effect on DEA may have varied between sampling time, increasing by up to 10 the denitrification rate of 6-day-old PRB and decreasing by up to 5 the denitrification rate of 21-day-old PRB. The present results suggest that indirect effects of warming through changes in bacterial community composition, coupled to the strong direct effect of temperature on DEA already demonstrated in PRB, could modulate dissolved nitrogen removal by denitrification in rivers and streams.
微生物反硝化作用是淡水生态系统中主要的脱氮过程。本研究旨在展示水变暖（+2.5°C）是否以及如何驱动细菌多样性和结构，以及细菌多样性如何影响光养河流生物膜（PRB）中的反硝化酶活性。我们使用与核电站冷却回路的即时热释放相关的水变暖来产生天然 PRB 组合在玻璃幻灯片上，同时测试 2 个温度（平均温度为 17°C 与 19.5°C）。在两个温度下，在 PRB 积累过程中（6 和 21 天）的两个采样时间点对 PRB 进行采样。使用 ARISA 评估细菌群落组成。通过 q-PCR 和 qRT-PCR 分别估计反硝化菌群落丰度和反硝化基因 mRNA 水平，分别为编码反硝化关键酶的催化亚基的 5 个基因。通过乙炔阻断测定法在 20°C 下测量反硝化酶活性（DEA）。平均 2.5°C 的水变暖足以产生对比鲜明的总细菌和反硝化菌群落，从而影响 DEA。DEA 可能受到间接温度效应的影响，这种影响在采样时间之间有所不同，6 天大的 PRB 的反硝化速率增加了 10%，21 天大的 PRB 的反硝化速率降低了 5%。本研究结果表明，通过改变细菌群落组成间接影响以及已经在 PRB 中证明的温度对 DEA 的直接强烈影响，可能会调节河流和溪流中的溶解态氮去除。
