Rhizosphere priming and plant-mediated cover crop decomposition.

Background and aims: Rhizosphere priming occurs when plant belowground carbon (C) allocation influences the rate of soil organic matter (SOM) decomposition. We investigated the effects of priming and plant-mediated cover crop decomposition on agroecosystem C and nitrogen (N) dynamics. Methods: Using C stable isotopes, we tracked C and N from corn, clover ( Trifolium pratense) and rye ( Secale cereale) cover crop litter, and background SOM in plots following clover, rye, or no cover crop (fallow) in 2013 and 2014. Results: Corn enhanced the decomposition of N-rich clover cover crop litter in 2013, but there was little evidence of priming of bulk SOM decomposition. There was no corn effect on litterbag decomposition in 2014, likely due to greater soil moisture and temperature in no-corn plots. Corn N uptake per unit of corn-derived CO respiration was consistently lower following rye than clover and fallow, suggesting a higher C cost for corn to access N following a rye cover crop. Conclusions: This is one of the first field-based studies to provide evidence that plant-mediated litter decomposition potentially provides an important source of plant-available N. Climate and residue quality influence the extent to which corn mediates its own N supply with implications for agroecosystem C and N cycling. [ABSTRACT FROM AUTHOR]