Discovering the physiological mechanisms and factors that influence underground nitrogen transfer from legumes to nonlegumes

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Why any organism would give up a limiting resource is a compelling idea and question worthy of investigation. Nitrogen (N) is the most critical nutrient that limits yield production and therefore, modern agriculture highly depends on synthetic N fertilizer application. Most plant species depend on the uptake of soil/fertilizer N to satisfy their needs; certain species, most notably the legumes, are capable of fixing unavailable atmospheric N2 via a symbiotic relationship with a special group of beneficial bacteria (rhizobia) that lives inside root nodules and make nitrogen available to the host plant. Non-nitrogen fixing plants (nonlegumes) can also be benefitted from this fixed N by legumes, especially through belowground N transfer from legumes to nonlegumes. Fixed N by legumes is transferred to non-legumes (e.g. corn, grass) via three pathways: 1) decomposition of legume root tissues and uptake of mineralized N compounds by neighbouring non-legumes; 2) uptake of N-containing legume root/nodule exudates by non-legumes; and 3) N transfer mediated by plant-associated mycorrhizae. However, biological N fixation is a very energy-intensive process and it costs a substantial amount of energy (ATP) for the host legume plant. The fundamental question arising here is the reason that a plant releases its most valuable nutrient (N) into the surrounding environment through the root system. The overall hypothesis that there is a direct relationship between legume N release and belowground N transfer from legumes to non-legumes. Additionally, the physiological mechanisms behind belowground N transfer routes still remain unknown. Therefore, here I want to find answers to this fundamental question with major implications for future agricultural improvement: What are the major biotic/abiotic factors that induce/reduce N release and transfer from legumes to non-legumes, how different biotic/abiotic factors affect N transfer pathways? How do N-containing root/nodule exudates shape rhizosphere/soil microbiomes to benefit legume and non-legume plants? How do neighbouring non-legumes influence N release from legumes, especially under the predicted future climate change scenario? These underground hidden mechanisms need to be understood in order to improve N use efficiency in cropping systems and reduce environmental pollution especially associated with nitrate leaching. The ultimate long-term goal is to manipulate crop genotypes, cropping systems and management practices to maximize N use efficiency, combat climate change, and achieve long term environmental sustainability. The results of the proposed research may thus help Canadian farmers as well as millions of subsistence farmers around the world who rely on agriculture. The project will recruit talented students, train and prepare them to become independent and confident scientists who can build their own research programs and/or become leaders in the industry sector nationally and internationally.