Biogeochemical cycling at the molecular level in intensive cropping systems

土壤健康退化仍然是对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重要因素之一。尽管其重要性，SOM和其中的碳（C）和氮（N）仍然知之甚少，在分子水平上很大程度上没有表征。了解SOM的分子组成，稳定性和营业额是至关重要的，以预测其动态响应作物管理和发展更可持续的农业实践。要做到这一点，我们必须更好地了解调节C和N转化的机制，以及对土壤生态系统服务的影响。新兴的分子技术已经从根本上改变了我们对SOM的理解，从以前长期持有的概念，SOM主要是植物输入的功能，他们的化学，和从头合成的大分子腐殖物质的新兴概念，稳定的SOM形成是由于微生物衍生的产品的分解和稳定的生物分子通过有机-矿物和有机-金属氧化物的相互作用。除了这些进展，在理解SOM，很少有研究已经评估了SOM的动态在分子水平上的集约化种植系统，而研究主要集中在非管理系统。可以说，在集约化管理的种植系统中了解SOM更重要，不仅因为土壤健康退化的风险更高，而且随着全球人口的增长，管理系统可能会扩大-特别是集约化蔬菜作物生产。至关重要的是，这些土壤的生产力得到维持/提高，以可持续地养活不断增长的人口。这保证了研究，以更好地了解在集约化种植系统中的碳和氮化合物的股票和流动，因此我的研究计划的目的。在这里，我的目标是A）量化的影响，长期集约耕作的做法对土壤有机质的分子组成和营业额; B）评估土壤有机氮动态的变化，并将其贡献与作物氮的使用; C）调查SOM和N2 O排放之间的联系，作为生态系统服务功能的一个指标。我提出了一个新的方法组合：1）化合物特异性同位素分析（13 C和15 N）和同步加速器技术，以表征有机质的周转和分子组成; 2）稳定同位素富集，以联系土壤和植物养分动态; 3）将C和N基质与N的微生物处理相结合（和N2 O通量）使用腔衰荡光谱和同位素特征（N2 O-15 N）。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。我们的研究结果将对加拿大可持续种植系统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.