The key role of DOM in regulating microbial diversity, community structure and organic carbon cycling in arctic lakes

北极是一个相当大的有机碳库(~1672Pg)，这个碳库的陆地和水生加工基本上是由微生物调节的。为了预测北极变暖等快速变化的环境对生态的影响，迫切需要了解调节具有重要功能的微生物群落多样性和结构的机制。所有水生生态系统(湖泊、河流、海洋)都含有大量的溶解有机物(DOM)。DOM的含量可以超过生物体(植物、动物、微生物等)中所含的碳量。这些积累的有机物是光合作用、消耗和降解途径的产物，可以包含一系列物质，从百年前S时代的细菌难以分解的化合物，到最近从活的藻细胞光合作用中泄漏出来的有机物，这些有机物可以迅速被细菌和其他微生物利用。这种微生物活动为其他生物体制造食物，促进营养再生，并将有机物回收到食物链中。其他DOM可以粘在一起，被埋在沉积物中，并被锁住一段时间。水生系统中存在的大量DOM意味着，了解其特征和动态(生物地球化学循环)对于了解单个系统和产生准确的区域碳预算是必要的。关于DOM如何与在DOM生物地球化学中扮演如此重要角色的微生物群落相互作用，以及DOM的哪些方面有助于塑造微生物群落(例如，它是物种丰富的，还是物种贫乏的，主要活跃的还是主要不活跃的)，生态学中一直存在着争论。了解不同生态系统中物种多样性和生物地球化学循环之间的关系是NERC的优先议题。新的实验途径和方法意味着这些问题现在可以解决了。这个项目正在西格陵兰岛的一个湖泊系统中研究这些概念。这些湖泊具有一系列DOM浓度，并受到全球变化过程的影响，例如大气营养物质负荷增加和年度变暖。北极湖泊在其区域生态中极其重要；它们占据了相当大的陆地面积，根据其特征，可以充当年度碳汇或碳源。我们将描述一组湖泊水柱中不同的DOM成分，以提供可控的条件梯度，并确定DOM积累和损失的季节性周期。同时，我们将使用新的分子生物学工具来识别和量化参与这些过程的不同微生物群落。我们将能够确定微生物群落多样性和活性之间的关系，以及存在的DOM类型如何影响这一关系。我们还将进行实验，以确定哪些DOM最难分解，最容易被特定微生物分解，以及这些过程是否受到氮等营养物质的影响。这些结果将有助于评估北极地区的生态湖泊在未来几十年将如何变化，并提供关于DOM生物地球化学与微生物多样性和活动之间关系的重要信息，这些信息将适用于其他水生系统。这些新数据还将有助于发展关于微生物群落是如何构成的理论，以及它们是遵循为较大的生物体确定的规则，还是具有独特的特征。

The Arctic is a considerable organic carbon store (~1672 Pg) and the terrestrial and aquatic processing of this C pool is essentially mediated by microorganisms. Understanding the mechanisms regulating the diversity and structure of functionally-important microbial communities is urgently required for predicting the ecological impacts of rapidly changing environments, such as a warming Arctic. All aquatic ecosystems (lakes, rivers, the oceans) contain very substantial amounts of dissolved organic matter (DOM). The amount of DOM can exceed the amount of carbon contained in living organisms (plants, animals, microbes, etc.). This accumulated organic matter is the product of photosynthesis, consumption and degradation pathways, and can contain a range of material, from compounds that are 100's of years old, and are difficult for bacteria to break down, to recently produced organic matter that may have leaked from living algal cells as they photosynthesise, which can quickly be used by bacteria and other microorganisms. This microbial action generates food for other organisms, and promotes nutrient regeneration, and recycles the organic matter back into food chains. Other DOM can stick together and become buried in sediments and locked away for geological periods of time. The huge quantities of DOM present in aquatic systems mean that understanding its characteristics and dynamics (biogeochemical cycling) is necessary to understand individual systems and to generate accurate regional carbon budgets. There is an ongoing debate in ecology as to how DOM interacts with the microbial communities that play such an important part in DOM biogeochemistry, and what aspects of DOM help shape the microbial community (e.g. is it species rich, or species poor, mainly active or mainly inactive). Understanding the relationship between species diversity and biogeochemical cycling in different ecosystems is a priority topic for NERC. New experimental approaches and methods mean these questions can now be addressed. This project is investigating these concepts in a system of lakes in West Greenland. These lakes have a range of DOM concentrations, and are being influenced by global change processes such as increased atmospheric nutrient loading and annual warming. Arctic lakes are extremely important in their regional ecology; they occupy significant land area and can act as annual carbon sinks or carbon sources, depending on their characteristics. We will characterise the different DOM components of the water columns of a set of lakes selected to provide a controlled gradient of conditions, and determine the seasonal cycles of accumulation and loss of DOM. In parallel, we will use new molecular biology tools to identify and quantify the diverse microbial communities involved in these processes. We will be able to determine the relationship between microbial community diversity and activity, and how this is influenced by the types of DOM present. We will also conduct experiments to establish which DOM are the most difficult and most easy for particular microbes to breakdown, and whether such processes are influenced by nutrients such as nitrogen. These results will help to assess how the ecology lakes in arctic regions will change over the next few decades, as well as providing important information on the relationships between DOM biogeochemistry and microbial diversity and activity that will be applicable to other aquatic systems. These new data will also contribute to the development of theories of how microbial community are structured, and whether they follow rules determined for larger organisms, or have unique characteristics.