To better understand linkages between hydrology and ecosystem carbon flux in northern aquatic ecosystems, we evaluated the relationship between plant communities, biofilm development, and carbon dioxide (CO2) exchange following long‐term changes in hydrology in an Alaskan fen. We quantified seasonal variation in biofilm composition and CO2 exchange in response to lowered and raised water table position (relative to a control) during years with varying levels of background dissolved organic carbon (DOC). We then used nutrient‐diffusing substrates (NDS) to evaluate cause–effect relationships between changes in plant subsidies (i.e., leachates) and biofilm composition among water table treatments. We found that background DOC concentration determined whether plant subsidies promoted net autotrophy or heterotrophy on NDS. In conditions where background DOC was ≤ 40 mg L−1, plant subsidies promoted an autotrophic biofilm. Conversely, when background DOC concentration was ≥ 50 mg L−1, plant subsidies promoted heterotrophy. Greater light attenuation associated with elevated levels of DOC may have overwhelmed the stimulatory effect of nutrients on autotrophic microbes by constraining photosynthesis while simultaneously allowing heterotrophs to outcompete autotrophs for available nutrients. At the ecosystem level, conditions that favored an autotrophic biofilm resulted in net CO2 uptake among all water table treatments, whereas the site was a net source of CO2 to the atmosphere in conditions that supported greater heterotrophy. Taken together, these findings show that hydrologic history interacts with changes in dominant plant functional groups to alter biofilm composition, which has consequences for ecosystem CO2 exchange.

中文翻译：

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植物群落结构的遗留影响表现在微生物生物膜的形成中，对生态系统的二氧化碳排放产生影响


为了更好地了解北部水生生态系统中水文与生态系统碳通量之间的联系，我们评估了阿拉斯加沼泽地水文长期变化后植物群落、生物膜发育和二氧化碳 （CO2） 交换之间的关系。我们量化了在不同背景溶解有机碳 （DOC） 水平下，生物膜组成和 CO2 交换响应地下水位降低和升高（相对于对照）的季节性变化。然后，我们使用营养扩散底物 （NDS） 来评估地下水位处理中植物补贴（即渗滤液）变化与生物膜组成之间的因果关系。我们发现背景 DOC 浓度决定了植物补贴是促进 NDS 的净自养还是异养。在背景 DOC ≤ 40 mg L-1 的条件下，植物补贴促进了自养生物膜。相反，当背景 DOC 浓度≥ 50 mg L-1 时，植物补贴促进了异养。与 DOC 水平升高相关的更大光衰减可能通过限制光合作用压倒了营养物质对自养微生物的刺激作用，同时允许异养生物在可用营养物质方面超过自养生物。在生态系统层面，有利于自养生物膜的条件导致所有地下水位处理中的二氧化碳净吸收，而在支持更大异养的条件下，该地点是大气中二氧化碳的净来源。综上所述，这些发现表明，水文历史与主要植物功能群的变化相互作用，从而改变生物膜组成，从而对生态系统 CO2 交换产生影响。