Miss Francesca  Brailsford¹, Dr Helen Glanville², Professor Peter Golyshin¹, Dr Miles Marshall¹, Dr Charlotte Lloyd³, Professor Penny Johnes³, Professors Davey Jones¹

¹Bangor University, Bangor, United Kingdom, ²Keele University, Keele, United Kingdom, ³Bristol University, Bristol, United Kingdom

Dissolved organic matter (DOC) turnover in aquatic environments is modulated by the presence of other key macronutrients, including nitrogen (N) and phosphorus (P). The ratio of these nutrients directly affects the rates of microbial growth and nutrient processing in the natural environment. The aim of this study was to investigate how labile DOC metabolism responds to changes in nutrient stoichiometry using 14C tracers in conjunction with untargeted analysis of the primary metabolome in upland peat river sediments. N addition led to an increase in 14C-glucose uptake, indicating that the sediments were likely to be primarily N limited. The mineralization of glucose to 14CO2 reduced following N addition, indicating that nutrient addition induced shifts in internal C partitioning and microbial C use efficiency. This is directly supported by the metabolomic profile data which identified significant differences in 22 known metabolites (34% of the total) and 30 unknown metabolites (16 % of the total) upon the addition of either N or P. 14C-glucose addition increased the production of organic acids known to be involved in mineral P dissolution (e.g. gluconic acid, malic acid). Conversely, when N was not added, the addition of glucose led to the production of the sugar alcohols, mannitol and sorbitol, which are well known microbial C storage compounds. P addition resulted in increased levels of several amino acids (e.g. alanine, glycine) which may reflect greater rates of microbial growth or the P requirement for coenzymes required for amino acid synthesis. We conclude that inorganic nutrient enrichment in addition to labile C inputs has the potential to dramatically alter in-stream biogeochemical cycling in oligotrophic freshwaters.

Biography: After obtaining a BSc in Biochemistry at King’s College London, I returned to North Wales to study for an MSc in Marine Biology at Bangor University. I am completing my PhD part-time alongside my role as a Junior Research Technician on the NERC DOMAINE Project, which aims to characterise the nature, origins and ecological significance of dissolved organic matter in freshwater ecosystems. The project partners include the University of Bristol, Bangor University, The University of East Anglia and the Centre for Ecology & Hydrology (CEH). My research is part of Work Package 3 of the DOMAINE Project, which aims to identify the dominant metabolic pathways controlling stream and nutrient processing and uptake. Currently I am involved in the seasonal analysis of low-molecular weight (LMW) nutrient processing using both 14C and 33P labelling methods. Once this is complete a combination of microbial characterisation and metabolomic approaches will be used to identify the major microbial groups and nutrient pathways involved in in-stream processing. Information on the NERC DOMAINE Project can be found below: http://www.nerc-domaine.uk/ Future publications will be added to ResearchGate: http://www.researchgate.net/profile/Francesca_Brailsford