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

为什么任何生物体会放弃有限的资源是一个令人信服的想法和值得研究的问题。氮(N)是限制产量的最关键的养分，因此现代农业高度依赖于氮肥的施用。大多数植物依靠土壤/肥料氮的吸收来满足其需求；某些物种，尤其是豆科植物，能够通过与生活在根瘤内的一组特殊有益细菌（根瘤菌）的共生关系来固定大气中不可用的N2，根瘤菌为寄主植物提供氮。非固氮植物（非豆科植物）也可以从豆科植物的固定氮中获益，特别是通过豆科植物向非豆科植物的地下氮转移。豆科植物的固定氮通过三种途径转移到非豆科植物（如玉米、草）：1)豆科植物根组织的分解和邻近的非豆科植物对矿化氮化合物的吸收；2)非豆科植物对含氮豆科植物根/根瘤分泌物的吸收；3)植物相关菌根介导的氮转运。然而，生物固氮是一个非常能量密集型的过程，它为寄主豆科植物消耗大量的能量（ATP）。这里产生的根本问题是植物通过根系向周围环境释放最有价值的养分(N)的原因。总体假设豆科植物氮素释放与地下氮素从豆科植物向非豆科植物转移有直接关系。此外，地下氮转运途径背后的生理机制仍不清楚。因此，在这里，我想找到这个对未来农业改良具有重大意义的基本问题的答案：诱导/减少氮素释放和从豆类到非豆类转移的主要生物/非生物因素是什么？不同的生物/非生物因素如何影响氮素转移途径？含氮根/根瘤渗出物如何塑造根际/土壤微生物群，使豆科植物和非豆科植物受益？邻近的非豆科植物如何影响豆科植物的氮释放，特别是在预测的未来气候变化情景下？为了提高种植系统中氮素的利用效率，减少环境污染，特别是与硝酸盐淋溶有关的污染，需要了解这些地下隐藏机制。最终的长期目标是操纵作物基因型、种植制度和管理实践，以最大限度地提高氮素利用效率，应对气候变化，实现长期的环境可持续性。拟议的研究结果可能因此帮助加拿大农民以及世界各地数百万依赖农业的自给自足的农民。该项目将招募有才华的学生，培养和准备他们成为独立和自信的科学家，他们可以建立自己的研究项目和/或成为国内和国际行业的领导者。

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.