Priming Effects in the Rhizosphere of Maize: Mechanisms and Field Relevance

Thomas Splettstößer, Amit Kumar, Yue Sun, Johanna Pausch

DFG: 2014-2016 PA 2377/1-1

Fluxes of carbon (C) from soil to the atmosphere and of nitrogen (N) to the plants are mainly driven by turnover of soil organic matter (SOM). The release of organic substances by living roots into the soil (rhizodeposition) and the stimulation of microbial activity can provoke changes in the rate of SOM-decomposition termed 'rhizosphere priming effects' (RPE).
The aim of this project is to provide comprehensive understanding of RPE by assessing factors, mechanisms, intensities and dynamics of RPE in field and laboratory experiments and by investigating the relevance of RPE for agroecosystems.
Two main factors significantly affecting RPE will be intensively studied: the amount of the primer and the mineral N status of the soil. By combining various isotopic approaches (13C natural abundance, 15N labeling and 15N dilution) we will simultaneously trace C and N derived from SOM-decomposition in the field, thus, improving the understanding of priming effects at field scale.
The combination of 13C continuous labeling with a high-resolution d13C analysis of soil CO2 will provide short term dynamics of RPE and will allow to determine their dependence on plant growth stages and associated therewith, on root properties. Digital images of the distribution of exudates analyzed by 14C imaging and enzyme activities along single root segments (by zymography) will allow to study spatial dynamics of RPE. Furthermore, a new approach for estimating microbial groups involved in RPE will be tested. Based on the mechanisms of priming effects the functioning of C and N turnover in rhizosphere will be clarified.

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