A Nutrient-Centric View of Rhizosphere Priming: Corn Mediation of Cover Crop Litter Decomposition and Nitrogen Cycling.

Plants can influence many soil processes through rhizosphere-microbe interactions, including the rhizosphere effects on soil organic matter decomposition. Understanding rhizosphere dynamics may also offer an opportunity to improve the synchrony of nitrogen (N) mineralization and plant N uptake. We tracked the carbon (C) and N from growing corn (Zea mays), soil organic matter, and cover crop litter in a greenhouse study. We hypothesized that corn would increase the decomposition rate of cover crop litter and that the corn effect would differ by cover crop type. Litterbags of 2mm and 35um mesh with root or shoot litter from clover (Trifolium pratense), rye (Secale cereale), or a mixture of clover-rye were buried in each of four replicate pots with and without corn plants. We used C and N stable isotopes to differentiate between corn-derived and cover crop C and N sources. Corn stimulated cover crop litter C and N loss and the corn effects were greatest for clover shoot and clover-rye mixed root material. Corn increased relative belowground C allocation when cover crop litter was present. When corn roots were excluded from litterbags, corn acquisition of N from litter was reduced and microbial N from litter increased, regardless of litter type. This indicates that direct contact between litter and plant roots was required for priming of litter decomposition and improved crop competition for mineralized N. From this study and previous field studies, we have found consistent evidence of corn priming the decomposition cover crop litter, but limited evidence of corn priming the decomposition of soil total soil organic carbon pools. These results suggest that plant mediation of litter decomposition is influenced by litter quality with consequences for crop carbon allocation and agroecosystem nitrogen cycling.