Biogeochemistry of Desert Crusts: Organic Carbon and Trace Element Dynamics

干旱的沙漠环境是一个独特的微生物-矿物系统的家园，在这个系统中，蓝藻和微藻形成了生物土壤结皮。这些系统很重要，因为它们显著影响干旱地区的碳循环和养分收支，而且它们可能是陆地植物兴起之前早期陆地生物群的代表。生物土壤结皮存在于一个严重受限于缺乏水和养分的环境中，特别是缺乏生物必需的微量金属。我们假设，生物土壤结皮通过生产有机化合物来最大限度地保持水分和养分。土壤结皮群落对土壤中有机化合物和生物必需金属的调节作用，为微生物和地球物质之间提供了基本的生物地球化学联系。我们的实验研究集中在土壤结皮微生物与矿物基质的相互作用，以及土壤孔隙水产生和/或流失的有机化合物的性质和对代谢相关金属的影响。我们的具体目标是：1)表征荒漠土壤结皮及其下层土壤矿物学和地球化学性质；2)比较结皮和未结皮土壤系统的碳和微量元素组成；3)模拟降雨事件，评估生物土壤结皮有机碳生产和金属分布在水暴露之前、期间和之后的变化。电喷雾电离串联质谱仪将用于直接从水样中鉴定特定的有机化合物，而电感耦合等离子体质谱将用于确定痕量金属的浓度和分布。有机生物地球化学、微量元素生物地球化学和地质微生物学的这种结合是相当不寻常的，我们的研究生和本科生将获得独特的跨学科研究经验。

Hartnett0525569Arid desert environments are home to a unique microbe-mineral system in which cyanobacteria and microalgae form biological soil crusts. These systems are important because they significantly impact the carbon cycle and nutrient budgets in arid regions, and because they may be representative of early terrestrial biota before the rise of land plants. Biological soil crusts exist in an environment profoundly limited by the lack of water and nutrients, especially bioessential trace metals. We hypothesize that biological soil crusts maximize their retention of water and nutrients through the production of organic compounds. The soil crust community's mediation of organic compounds and the bioessential metals in the soil provides a fundamental biogeochemical link between microbes and earth-materials. Our experimental studies focus on the interactions of soil crust microbes with mineral substrates, and the nature and effects of the organic compounds produced and/or lost to the soil porewater on metabolically relevant metals. Our specific objectives are: 1) To characterize desert soil crust and the underlying soil mineralogy and geochemistry; 2) To compare crusted and uncrusted soil systems with respect to carbon and trace element composition; 3) To simulate rain events and assess changes in biological soil crust organic carbon production and metal distributions before, during and after water exposure. Electrospray ionization tandem mass spectrometry will be used to identify specific organic compounds directly from water samples, and ICP-mass spectrometry will be used to determine trace metal concentrations and distributions. This integration of organic biogeochemistry, trace element biogeochemistry, and geomicrobiology is quite unusual and our graduate and undergraduate students will gain unique trans-disciplinary research experience.