Nitrification as function of nutrient limitation and stoichiometry

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Global agricultural N fertilization is steadily increasing, providing N to plants, but also to soil microorganisms such as ammonia oxidizers and nitrite oxidizers, e.g. Nitrosomonas and Nitrobacter, which exert an essential influence on the production of nitrate (NO3-) and nitrous oxide (N2O) as potential pollutants of the hydrosphere and atmosphere. Both heterotrophic and nitrifying microorganisms have specific stoichiometric C:N:P requirements. Most nitrifiers are autotrophic and able to gain energy for their biochemical activity and growth based on CO2 and the oxidation of mineral N (NH3). Under organic C-limited conditions and increased N and P availability, production of NO3- and N2O due to nitrification might be increased. Aim of this project is to evaluate if organic C limitation and N:P stoichiometry indeed are important regulators of nitrification. Experiments will be performed under highly controlled laboratory conditions. NO3-, N2O, C:N:P stoichiometry, microbial nutrient limitation, and autotrophic nitrifier abundance will be measured during progressive decomposition of labile organic C. It is expected that C:N:P stoichiometry has significant influence on N dynamics and consequently on agricultural nitrogen use efficiency, particularly during transition to the decomposition phase with limited C availability.