Direct and indirect trophic interactions of soil nematodes impact chickpea and oat nutrition

Aims: Root lesion nematodes (RLN) have negative impacts on legume-grass systems. These impacts might be moderated by bacterial feeding nematodes (BFN) presence. It remains unknown how these trophic groups of nematodes interactively impact plant productivity and dynamics of carbon (C) and nitrogen (N) in grass-legume mixtures. We addressed this research gap using inter-kingdom interactions in a model system. Methods: Chickpea and oat were grown in mono- and mixed cultures, and RLN and BFN were applied alone and in combination. Plant biomass, shoot C and N content and isotopic composition, and mineral N in soil were measured. Results: RLN presence reduced root biomass across treatments. This reduction was stronger in the grass than the legume and was not modified by BFN. Nematodes increased plant shoot N concentrations. RLN and BFN had interactive effects on shoot nutrient concentration resulting in reduced shoot C concentration when both trophic groups were combined. Shoot δ15N data revealed transfer of symbiotically fixed N from chickpea to oat in the presence of RLN. However, this N transfer did not result in improved oat growth. Conclusions: Interactive effects of soil organisms can cascade aboveground, influencing C and N dynamics and ecosystem productivity.