Competitive patterns of N partitioning between plants and microorganisms in intact plant-soil-systems

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Our knowledge on ecosystem N cycling processes is largely falsified by the disregard of plant-microbe interactions and -competition for N, and by the enormous variability of belowground N fluxes in space and time. To elucidate competitive patterns of N partitioning between beech and microorganisms and its responses to changing environmental conditions, stable isotopes (15N, 13C) will be followed in field experiments, lysimeter and microcosm studies through the plant-soil system. Triple labelling approaches (15N/13C glutamin, 15NH4 +, 15NO3 -) in mini-lysimeters in combination with 15N tracing modelling will allow to simultaneously mimic major N fluxes in intact plant-soil systems, and thus, to characterize plant-microbe competition in a process-oriented way. Furthermore, N2 and N2O emissions from intact soil cores will be measured directly in order to quantify the role of denitrification in the competition for NO3 - . Near infrared spectroscopy (NIRS) will be used to measure indicators of competition for N with high resolution in order to overcome the high temporal and spatial variation of N fluxes and competitive patterns of N partitioning.