Postdoctoral Fellowship: EAR-PF: Linking soil nitrogen enrichment to mineral weathering and associated organic matter persistence

土壤储存了大量的有机物质--比大气或土地的总和还要多！土壤有机质主要由碳组成，如果土壤中的微生物可以利用它，它们就会“吃掉”这种有机物，并呼吸二氧化碳(CO2)。随着气候危机继续改变当地的温度和降水，我们想知道SOM将如何留在地下，而不是以二氧化碳的形式释放到大气中。帮助碳留在土壤中的一种机制，我们称之为SOM持久性，是SOM颗粒和矿物之间的正负电荷，矿物来自破碎成小块的岩石。将岩石分解成有助于保护有机质免受微生物侵袭的矿物的过程称为风化。在基岩或母质含有大量矿物质的土壤中，这些矿物质可以随着流经土壤的水分、温度和酸量的增加而释放。硝酸是生物固氮过程中自然产生的一种酸，豌豆和豆类等具有共生细菌的植物可以做到这一点。在拥有大量固氮植物的土壤中，更多的硝酸可能有助于风化母质并释放有助于保护SOM的矿物质，从而导致更多的碳持久性。该项目将研究岩石被硝酸风化之间的关系，以及它与土壤碳储量之间的关系，从浅层土壤到深层土壤，以及跨具有低风化和高风化母质的生态系统。被选来研究俄勒冈州森林长期氮浓缩梯度的地点还提供了一个机会，通过鼓舞人心的女孩远征与正在进行的外联工作合作，并扩大目前的旅行范围，将森林生态系统包括在内。这项计划将是一种免费的教育体验，高中生认为是女性，非二元，或性别酷儿，并不会选择学生参加这项计划将不基于传统的学术基准，如成绩和考试成绩。取而代之的是，学生将根据他们对临界区科学的兴趣和这个项目可能改变他们未来的程度来选择。鉴于矿物相互作用在碳固存和储存中的SOM持久性的重要性，了解影响矿物相关有机质(MAOM)形成和持久性的过程是当务之急。尽管生物固氮和人为沉积在全球生态系统中引入了大量的N，但硝酸对风化和随后的MAOM持久性的影响尚未被研究。这项研究的长期目标是了解氮的富集度和硝酸风化如何影响不同气候和主要矿物风化状态的MAOM丰度和持久性。这项研究将量化长期土壤氮富集下的MAOM丰度和短期硝酸盐和硝酸输入后的MAOM损失。这些配对实验将阐明MAOM的形成和不稳定是如何在不断增加的氮浓缩以及更多和更少风化的玄武岩母质之间共同发生的。由于深层土壤储存了大量的土壤碳，这一建议的另一个目的是了解矿物质组合对土壤有机质的保护以及随深度的不稳定。尽管在理解MAOM和矿物组合的广泛模式方面取得了重大进展，但关键的机械问题仍未得到检验。氮素的增加对土壤有机碳的影响在理解土壤有机碳的形成和持久性以及土壤碳储存方面构成了一个重要的知识鸿沟。这项建议通过将短期和长期的氮浓缩与MAOM的精细地球化学驱动因素联系起来，促进了临界区科学方面的知识。迫切需要了解和预测土壤中可以储存多少碳(C)，以及这种碳的持久度。这项工作为提高MAOM预测的准确性和面对全球变化的陆地C循环模型的准确性提供了机会。通过调查土壤氮梯度、温带和热带气候之间以及低风化玄武岩母质土壤和高风化玄武岩母质土壤之间的MAOM丰度，这些发现可以应用于许多经历N丰度的生态系统。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Soils store a huge amount of organic matter - more than the atmosphere or land combined! Soil organic matter is mostly made up of carbon, and if it becomes available to microbes living in the soil, they will “eat” this organic matter and respire carbon dioxide (CO2). As the climate crisis continues to alter local temperatures and precipitation, we want to understand how the SOM will stay in the ground instead of being released to the atmosphere as carbon dioxide. One mechanism that helps carbon stay in the soil, which we call SOM persistence, are positive and negative charges between SOM particles and minerals, which come from rocks broken into tiny pieces. The process of breaking rocks down into minerals that help protect SOM from microbes is called weathering. In soils where the bedrock, or parent material, has a lot of minerals, these minerals can be released with increasing amounts of moisture, temperature, and acids that flow through the soil. Nitric acid is a naturally produced acid from biological nitrogen (N) fixation, which plants like peas and beans with their symbiotic bacteria can do. Across soils that have a lot of N fixing plants, more nitric acid may have helped to weather parent material and release minerals that can help protect SOM, leading to more carbon persistence. This project will investigate the relationship between rock weathering by nitric acid and how it relates to soil C storage from shallow to deep soils, and across ecosystems with low and high weathered parent material. The sites chosen to study the long-term N enrichment gradient in Oregon forests also provide an opportunity to collaborate with ongoing outreach efforts through the Inspiring Girls Expeditions and expand the current trips to include forest ecosystems. This program will be a no-cost educational experience for high school students identifying as women, non-binary, or genderqueer, and selection of students to this program will not be based on traditional academic benchmarks such as grades and test scores. Instead, students will be chosen based on their interest in Critical Zone sciences and the degree to which this program may change their futures.The need to understand the processes that affect mineral-associated organic matter (MAOM) formation and persistence are imperative given the importance of SOM persistence by mineral interactions in C sequestration and storage. Though biological nitrogen (N) fixation and anthropogenic deposition introduce significant quantities of N in ecosystems across the globe, the effects of nitric acid on weathering and subsequent MAOM persistence has not been studied. The long-term goal of this research is to understand how N enrichment and nitric acid weathering affects MAOM abundance and persistence across climates and primary mineral weathering states. This research will quantify both MAOM abundance under long-term soil N-enrichment and MAOM loss after short-term nitrate and nitric acid inputs. These paired experiments will clarify how MAOM formation and destabilization co-occur across increasing N enrichment and between more and less weathered basalt parent material. Because deep soils store a substantial amount of soil C, an additional aim of this proposal is to understand SOM protection by mineral-associations and destabilization with depth. Despite the significant gains in understanding broad patterns of MAOM and mineral associations, key mechanistic questions remain untested. The effects of N enrichment on MAOM constitutes a significant knowledge gap in the understanding of MAOM formation and persistence, and consequently, soil C storage. This proposal advances knowledge in Critical Zone science by linking short and long-term N enrichment with fine-scale geochemical drivers of MAOM. There is an urgent need to understand and predict how much carbon (C) can be stored in soils and the degree to which this carbon persists. This work offers an opportunity to improve the accuracy of MAOM predictions and the accuracy of terrestrial C cycling models in the face of global change. By investigating MAOM abundance in soils across a gradient of soil N, between temperate and tropical climates, and between soils of low and high weathered basalt parent material, these findings can apply to many ecosystems that experience N enrichment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.