Collaborative Research: Exploring the dynamic interaction between pyrogenic carbon and extracellular enzymes and its impacts on organic matter cycling in fire-impacted environments

无论是自然发生还是人类活动引起的火灾，都会对许多生态系统和全球碳 (C) 循环造成普遍干扰。火灾将大量生物质转化为二氧化碳和热解碳 (PyC)，并在土壤中积累。由于其丰富和独特的理化性质，PyC 可能参与许多控制重要元素循环和土壤健康的土壤生物地球化学过程。然而，人们对 PyC 如何在土壤中分解以及 PyC 如何影响土壤微生物群落（土壤有机质（SOM）分解的主要驱动因素）仍知之甚少。由于SOM的微生物分解是由微生物释放的酶（外切酶）催化的，因此本项目将研究PyC如何与外切酶相互作用，以及哪些酶能够降解PyC。这项工作的结果将从根本上增进目前对 PyC 循环及其对全球 C 循环贡献的理解。来自合作机构的两名研究生和几名本科生将接受生物地球化学、酶学和分析化学等跨学科培训。该团队将与当地学校和博物馆合作，开展 K-12 和社区外展活动，以提高公众对火灾在气候和土壤科学中的作用的认识。该项目的总体目标是探索 PyC 在微生物介导的 SOM 降解中的作用，特别是它对土壤中外酶功能的直接影响。考虑到 PyC 整体较大的比表面积和吸附能力，首先将评估 PyC 作为土壤吸附表面的作用。将探索不同燃烧条件和不同风化历史下产生的代表性外酶和 PyC 之间的相互作用机制，并确定控制相互作用的 PyC 和酶的关键特性。然后使用灵敏的量热分析确定 PyC 吸附对酶活性的影响。尽管已知微生物能够降解并利用 PyC 作为碳源，但降解过程和非生物风化的影响尚不清楚。因此，酶降解 PyC 的速率和结构转化，特别是那些降解芳香族结构的酶，将被确定。这项工作将采用一套整体方法来详细介绍固体和溶解的 PyC 的化学性质，并使用一套光谱技术。通过描述外酶的界面行为和功能以及控制 PyC 稳定性中非生物和生物风化过程之间的相互作用，这项工作产生的知识将从根本上增进我们对受火灾影响的环境中 SOM 循环的理解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Fires, whether occurring naturally or caused by human activities, are a pervasive disturbance to many ecosystems and the global carbon (C) cycle. Fires convert tremendous amounts of biomass into CO2 and pyrogenic carbon (PyC) that accumulates in soils. Because of its abundance and unique physicochemical properties, PyC may participate in many soil biogeochemical processes that control the cycling of important elements and soil health. However, it remains poorly understood how PyC is decomposed in soil and how PyC may affect the soil microbial community – the main driver of soil organic matter (SOM) decomposition. Because microbial decomposition of SOM is catalyzed by enzymes released by microbes (exoenzymes), this project will study how PyC interacts with exoenzymes, and which enzymes are capable of degrading PyC. Results from this work will fundamentally advance the current understanding of the cycling of PyC and its contribution to the global C cycle. Two graduate students and several undergraduate students from the collaborating institutions will gain interdisciplinary training in biogeochemistry, enzymology, and analytical chemistry. In collaboration with local schools and museums, the team will develop K-12 and community outreach activities to increase general public’s awareness of the role of fires in climate and soil science.The overarching goal of this proposed project is to explore the roles of PyC in microbial-mediated SOM degradation, particularly its direct impacts on exoenzyme functioning in soils. The role of PyC as an adsorptive surface in soil will first be evaluated, considering its overall large specific surface area and adsorption capacity. Mechanisms of interaction between representative exoenzymes and PyC generated under different combustion conditions and of different weathering histories will be explored, and key properties of PyC and enzymes controlling the interaction will be identified. Then the impacts of PyC adsorption on enzyme activity will be determined using sensitive calorimetric analyses. Although microbes are known to be capable of degrading and utilizing PyC as a carbon source, the degradation process and effects of abiotic weathering are not clear. Therefore, the rate and structural transformation of PyC degradation by enzymes, particularly those that degrade aromatic structures, will be determined. This work will apply a holistic approach to detail the chemistry of solid and dissolved PyC, using a suite of spectroscopic techniques. By delineating the interfacial behaviors and functionality of exoenzymes and the interplay between abiotic and biotic weathering processes in controlling PyC stability, knowledge generated from this work will fundamentally advance our understanding of SOM cycling in fire-impacted environments.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.