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

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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.