Temporal dynamics of soil metabolites during rhizosphere priming in the vicinity of a root exudation hotspot

Kaltenburg-Lindau

2019

Sonderdruck

40000968

The input of labile C into soil is thought to accelerate microbial decomposition of soil organic matter in the socalled ‘rhizosphere priming effect’. However, plant roots release labile organic substances into spatially and temporally
constrained volumes of soil, resulting in a heterogeneous distribution of spots with dramatically increased C concentrations in the soil. Subsequent microbial and chemical dynamics, which may lead to a priming effect, are
likely to take place in the immediate vicinity of these exudation spots. So far, we lack an understanding of these
small-scale dynamics occurring during a priming event. The aim of this study was to investigate the fine-scale temporal dynamics of microbial activity and soil chemistry in response to simulated root exudation at distinct spots in undisturbed soil cores. Therefore, we used microdialysis, which allows the collection or release of organic compounds via diffusion across a very fine membrane. We placed microdialysis membranes (10 mm length, 500 m outer diameter, 20 kDa molecular weight cut-off) into undisturbed soil cores collected from a forest site and simulated a pulse of root exudation by releasing a mixture of 13C-labelled labile substrates (glucose, fructose, acetate, and succinate) for 8 hours (‘reverse microdialysis’), while simultaneously collecting metabolites from the soil solution at an hour-scale time resolution. In the 12 days after the pulse, we continued collecting metabolites and measured 13C in soil respiration in regular intervals to
assess substrate-induced respiration, soil organic matter (SOM) mineralization and priming effects.