Colorado State University Fort Collins, Colorado, United States
Crop breeding in highly modified soil nutrient environments may have altered how plants interact with their soil microbiome and resulting rhizosphere nutrient cycling processes. With growing focus on improving soil health in agroecosystems, it is important to understand which crop genotypes and traits may be best adapted to nutrient cycling dynamics under agricultural management practices that emphasize organic nutrient inputs. We sought to understand how genotypes of winter wheat with distinct belowground allocation patterns would respond to contrasting nutrient management strategies (long-term compost application vs. not) in terms of belowground carbon allocation, rhizosphere community processes, and nitrogen mobilization dynamics. Using greenhouse and field experiments, we examined rhizosphere community structure and functions related to nitrogen cycling through amplicon sequencing and enzymes assays, and followed the uptake of residue-derived nitrogen using 15N-labelled cover crop residue. In the greenhouse, we also used 13C labelling to assess root and exudate dynamics into soils.
Our results showed that genotypes responded differently, in terms of root exudation and N-mineralization dynamics, and this response depended on the soil compost amendment history. Root exudation (measured as wheat-derived dissolved organic carbon) was over 3-fold higher in the no-compost soil, with a 2-fold difference across genotypes. Interestingly, we found that the genotype with higher exudation was more responsive to soil management history, with over 4-fold change in exudation across soils, from compost-amended to no compost. Enzyme activity was affected by compost treatment but did not show an effect of genotype. However, indicator taxa analysis identified more microbial taxa associated with the high-exudation genotype. Across greenhouse and field experiments, uptake of residue N showed an 45%-82% change between genotypes, with the effect dependent on the soil management history. Our findings suggest that the ability of different crop genotypes to access complex organic nitrogen sources should be considered in breeding programs and in crop selection, especially as greater reliance on organic fertilizer sources can improve nutrient retention and soil health in agroecosystems globally.