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

为什么任何生物都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）是限制产量生产的最关键的营养素，因此，现代农业高度依赖于合成氮肥的施用。大多数植物物种依赖于土壤/肥料N的吸收来满足其需求;某些物种，最显著的是豆类，能够通过与生活在根瘤内的一组特殊的有益细菌（根瘤菌）的共生关系来固定不可利用的大气N2，并为宿主植物提供氮。非固氮植物（非豆科植物）也可以从豆科植物固定的氮中受益，特别是通过地下氮从豆科植物转移到非豆科植物。豆科植物固定的氮素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）植物相关真菌介导的氮素转移。然而，生物固氮是一个非常能量密集型的过程，它消耗了大量的能量（ATP）的主机豆科植物。这里出现的基本问题是植物通过根系向周围环境释放其最有价值的养分（N）的原因。总的假设，有一个直接的关系，豆科植物N释放和地下N转移从豆科植物到非豆科植物。此外，地下N转移途径背后的生理机制仍然未知。因此，在这里，我想找到这个基本问题的答案与未来的农业改进的主要影响：什么是主要的生物/非生物因素，诱导/减少氮释放和转移从豆科植物到非豆科植物，如何不同的生物/非生物因素影响氮转移途径？含氮根/根瘤分泌物如何塑造根际/土壤微生物群落，使豆科和非豆科植物受益？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？这些地下隐藏的机制需要了解，以提高作物系统中的氮素利用效率，减少环境污染，特别是与硝酸盐淋溶。最终的长期目标是操纵作物基因型，种植制度和管理措施，以最大限度地提高氮的利用效率，应对气候变化，并实现长期的环境可持续性。因此，拟议研究的结果可能有助于加拿大农民以及世界各地数百万依赖农业的自给农民。该项目将招募有才华的学生，培训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计划和/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.