VANADIUM K-EDGE XANES STUDY OF LEAF LITTER AND SOILS: VANADIUM SPECIATION

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 许多生态系统的碳固定和生产力受到氮素可利用性的限制，土壤细菌的固氮作用是陆地系统氮素的重要来源。 一个潜在的重要控制土壤和落叶中的固氮是化学形态和生物利用度的V，Mo和Fe，因为它们是所需的金属辅因子固氮酶，负责生物固氮酶。 我们将钒K边XANES研究V氧化态和配位几何与其他实验相结合，使用NMR和EPR来（1）表征落叶和土壤中V的形态和氧化还原转化，以及（2）阐明V在这些环境中的化学形态如何控制其对非共生固氮生物的生物利用度，以及钒的形态是如何影响陆地生态系统中游离固氮菌的分布和活性的。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Carbon fixation and productivity of many ecosystems are limited by the availability of nitrogen, and N2 fixation by soil bacteria is an important source of nitrogen to terrestrial systems. A potentially important control on nitrogen fixation in soils and leaf litter is the chemical speciation and bioavailability of V, Mo, and Fe because they are required metal cofactors in nitrogenase, the enzyme responsible for biological N2 fixation. We are combining a vanadium K-edge XANES study of V oxidation state and coordination geometry with other experiments using NMR and EPR to (1) characterize the speciation and redox transformation of V in leaf litter and soils, and (2) elucidate how the chemical speciation of V in these environments controls its bioavailability to asymbiotic diazotrophs, and thus how V speciation influences the distribution and activity of free living nitrogen fixers in terrestrial ecosystems.