Arid 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.
