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

火灾，无论是自然发生的，还是由人类活动引起的，都是对许多生态系统和全球碳(C)循环的普遍干扰。火灾将大量的生物质转化为积累在土壤中的二氧化碳和热解碳(PYC)。由于其丰富和独特的物理化学性质，PYC可能参与许多土壤生物地球化学过程，控制重要元素的循环和土壤健康。然而，对于热解碳在土壤中是如何分解的，以及热解碳如何影响土壤微生物群落--土壤有机质(SOM)分解的主要驱动力--仍然知之甚少。由于微生物分解SOM是由微生物释放的酶(外源酶)催化的，因此本项目将研究PYC如何与外源酶相互作用，以及哪些酶能够降解PYC。这项工作的结果将从根本上促进目前对PYC循环及其对全球C循环的贡献的理解。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、酶学和分析化学的跨学科培训。该小组将与当地学校和博物馆合作，开展K-12和社区推广活动，以提高公众对火灾在气候和土壤科学中的作用的认识。这项拟议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，特别是它对土壤外酶功能的直接影响。考虑到其大的比表面积和吸附能力，首先将评估PYC在土壤中作为吸附表面的作用。将探索不同燃烧条件和不同风化历史下产生的具有代表性的胞外酶和PYC之间的相互作用机理，并确定PYC和控制相互作用的酶的关键性质。然后，将使用灵敏的量热分析来确定PYC吸附对酶活性的影响。虽然已知微生物能够降解和利用热解碳作为碳源，但非生物风化的降解过程和影响尚不清楚。因此，将确定酶，特别是那些降解芳香族结构的酶降解PYC的速度和结构变化。这项工作将应用一种整体的方法来详细描述固体和溶解的PYC的化学组成，使用一套光谱技术。通过描绘外源酶的界面行为和功能，以及非生物和生物风化过程在控制PYC稳定性方面的相互作用，这项工作产生的知识将从根本上促进我们对火灾影响环境中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优势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.