SGER: Exploration of Three-Dimensional Structure in Sedimentary Organic Matter

土壤和潮间带沉积物经常受到干湿循环的影响。大多数表层土壤夏天是湿的，冬天是干的。由于涨潮和退潮，盐沼和潮间带沉积物可能每天都有干湿循环。在干燥条件下，脱水可以改变土壤和沉积物的三维(3D)结构；因此，干燥的沉积物可能与未干燥的沉积物表现不同。例如，由于干燥，在许多类型的土壤中经常可以看到憎水性(或疏水性)。此外，干燥土壤的有机质比未干燥土壤更容易降解。同样，水果和蔬菜的有机基质在脱水后可能会不可逆转地崩溃。在探索性研究基金(SGER)的支持下，纽约州立大学石溪分校的研究人员将研究有机物的结构在其分解反应中所起的作用。他们假设，有机质的三维结构和极性是控制盐沼沉积物分解的重要因素。覆盖在矿物表面或以碎屑形式存在的有机物的疏水基团暴露在海水中，具有高度水化的3D结构。3D结构中的有机分子是亲水性和极性的，允许其他极性有机化合物通过静电力被其3D结构吸收或分配到3D结构中。在干燥过程中，有机分子的极性官能团被迫相互作用或与矿物表面相互作用，从而导致极性部分翻过来，暴露出更多的疏水基团。干燥过程使有机物改变其构象，收缩其体积，并变得更加疏水性。再湿的有机物比未干燥的有机物疏水性更强，因此对非极性有机物的吸附能力比原始有机物更强。因此，在干湿循环的环境中，有机物的三维结构和极性可能会影响疏水或亲水化合物在溶液和颗粒相之间的分布。这将极大地影响有机物的再矿化速度。研究人员将进一步探索一些初步发现，即有机物的三维结构对海岸沉积物的吸附行为至关重要。具体地说，他们将研究(1)在这个3D结构中陆地有机物与海洋有机物的重要性，以及(2)3D性质对有机物再矿化率的重要性。作为一个明显的更广泛的影响，该项目有助于更好地从机制上理解有机物质再矿化，从而促进全球碳循环，从而产生社会影响。如果能够对海洋对二氧化碳水平上升的反应有更深入的了解，那么就有可能在政治选择之间做出更合理的选择。沿海沉积物含有世界海洋中的大部分沉积有机碳。

Soils and intertidal sediments are often subjected to wet-dry cycles. Most surface soils are wetted in summer and dried in winter. Salt marsh and intertidal sediments can have daily wet-dry cycles due to the rising and falling tide. Under dry conditions, dehydration can alter the three dimensional (3D) structure of soils and sediments; thus dried sediments may behave differently than never-dried sediments. For example, water repellency (or hydrophobicity) is often seen in many types of soils as a result of drying. Furthermore, dried soil organic matter is more easily degraded than non-dried soil. Similarly, the organic matrix of fruits and vegetables can collapse irreversibly after dehydration. With support from this Small Grant for Exploratory Research (SGER), researchers at the State University of New York at Stony Brook will investigate the role play by the structure of organic matter in its decompositional reactivity. They hypothesize that the three-dimensional structure and the polarity of organic matter are important factors controlling decomposition in salt marsh sediment. Hydrophobic groups of organic matter coating mineral surfaces or existing as detritus are exposed to seawater, and have a highly hydrated 3D structure. The organic molecules in the 3D structures are hydrophilic and polar, allowing other polar organic compounds to be absorbed by or partitioned into its 3D structure via electrostatic forces. During the drying process, polar functional groups of organic molecules are forced to interact with each other or with mineral surfaces, thus causing the polar moieties to turn inside out and expose more hydrophobic groups. The drying process makes organic matter change its conformation, shrink its volume, and become more hydrophobic. Rewetted organic matter is more hydrophobic than never-dried material and thus has a stronger sorption capacity for nonpolar organic compounds than the original organic matter. In environments with wet and dry cycles, the distribution of hydrophobic or hydrophilic compounds between solution and particulate phases could thus be influenced by the 3D structure and polarity of organic matter. This should greatly affect the rate of remineralization of the organic matter. The investigators will further explore some preliminary findings that the three-dimensional architecture of organic matter is critically important to sorption behavior of coastal sediments. Specifically, they will investigate (1) the importance of terrestrial versus marine organic matter in this 3D structure, and (2) the importance of the 3D nature to remineralization rates of organic matter. As a clear broader impact, this project has societal implications by contributing to a better mechanistic understanding of organic matter remineralization and thus the global carbon cycle. If a more sophisticated understanding of the ocean's response to increased levels of carbon dioxide can be developed, then more reasonable choices between political alternatives are possible. Coastal sediments contain much of the sedimentary organic carbon in the world oceans.