Biogeochemical cycling at the molecular level in intensive cropping systems

土壤健康退化仍然是农业生态系统可持续性的持续威胁。土壤有机质是调节土壤健康和土壤生态系统服务功能的最重要因素之一。尽管SOM很重要，但其中的碳(C)和氮(N)仍然知之甚少，很大程度上没有在分子水平上进行表征。了解SOM的分子组成、稳定性和周转对于预测其在作物管理中的动态以及开发更可持续的农业实践都是至关重要的。要做到这一点，我们必须更好地了解碳和氮转化的调节机制，以及对土壤生态系统服务的影响。新兴的分子技术从根本上改变了我们对SOM的理解，从过去长期持有的认为SOM主要是植物输入、植物化学和大分子腐殖质从头合成的函数的概念，转变为稳定的SOM形成是由微生物衍生的分解产物和生物分子通过有机-矿物和有机-金属氧化物相互作用稳定的结果。除了在理解土壤有机质方面的这些进展外，很少有研究在分子水平上评估集约种植系统的土壤有机质动态；相反，研究主要集中在非托管系统上。可以说，在集约管理的种植系统中理解SOM更为重要，这不仅是因为土壤健康退化面临更高的风险，而且随着全球人口的增长，管理系统可能会扩大--特别是集约蔬菜作物生产。维持/提高这些土壤的生产力，以可持续地养活不断增长的人口，这一点至关重要。这需要研究更好地了解集约种植系统中碳和氮化合物的库存和流动；因此，我的研究计划的目的是。在这里，我的目标是A)量化长期集约耕作对SOM分子组成和周转的影响；B)评估土壤有机N动态的变化，并将其对作物N利用的贡献联系起来；C)调查SOM和N2O排放之间的联系，作为生态系统服务功能的指标。我提出了一种新方法的组合：1)化合物特定的同位素分析(13C和15N)和基于同步加速器的技术，以表征有机质的周转和分子组成；2)稳定的同位素富集法，将土壤和植物养分动态联系起来；以及3)利用腔衰荡光谱和同位素特征(N2O-15N)，将碳和氮基质与N(和N2O通量)的微生物加工联系起来。三名研究生和五名本科生将在这个创新的环境中接受培训。我们的发现将对加拿大可持续种植制度的发展产生重大影响。

Soil health degradation remains a constant threat to agroecosystem sustainability. One of the most important factors regulating soil health and the functioning of soil ecosystem services is soil organic matter (SOM). Despite its importance, SOM and the carbon (C) and nitrogen (N) therein remain poorly understood and largely uncharacterized at the molecular level. Understanding the molecular composition, stability, and turnover of SOM is critical to both predicting its dynamics in response to crop management and to developing more sustainable agricultural practices. To do this, we must better understand the mechanisms that regulate C and N transformations, and the implications for soil ecosystem services. Emerging molecular techniques have radically changed our understanding of SOM from the former long-held conceptualization that SOM was mostly a function of plant inputs, their chemistry, and the de novo synthesis of macromolecular humic substances to the emerging conceptualization that stable SOM formation is resultant from microbial-derived products of decomposition and the stabilization of biomolecules via organo-mineral and organo-metal oxide interactions. Apart from these advancements in understanding of SOM, very little research has evaluated SOM dynamics at the molecular level in intensive cropping systems'; rather, research has largely focused on unmanaged systems. It is arguably more important to understand SOM in intensively managed cropping systems, not only because soil health degradation is at a higher risk, but with a growing global population, managed systems are likely to expand - particularly intensive vegetable crop production. It is crucial that the productivity of these soils are maintained/enhanced to sustainably feed a growing population. This warrants research into better understanding the stocks and flows of C and N compounds in intensive cropping systems; hence the purpose of my research program. Here, I aim to A) quantify the influence of long-term intensive cropping practices on the molecular composition and turnover of SOM; B) evaluate the changes in soil organic N dynamics and link its contribution to crop N use; C) investigate the link between SOM and N2O emissions, as an indicator of ecosystem service functioning. I propose a combination of novel approaches: 1) compound-specific isotope analyses (of 13C and 15N) and synchrotron-based techniques to characterize the turnover and molecular composition of organic matter; 2) stable isotope enrichments to link soil and plant nutrient dynamics; and 3) linking C and N substrates to microbial processing of N (and N2O fluxes) using cavity ring down spectroscopy and isotopomer signatures (N2O-15N). Three graduate and five undergraduate students will be trained in this innovative environment. Our findings will have a significant impact on the development of sustainable cropping systems in Canada.