Quantifying Water Balance-Carbon Storage Relationships Using Oxygen Isotope Ratios of Plant Lipids.

The impacts of shifting climate zones on soil carbon (C) storage are poorly understood, although it functions as a major C pool. For example, in California’s Sierra Nevada Mountains, temperate forests occur across an elevation gradient with various stages of soil development, occupying several distinct climate zones. Soil development and C storage are strongly influenced by temperature, mineralogy, and local precipitation/evapotranspiration (ET) relationships, yet quantitative methods have not been established relating C storage to the latter. As a result, there is a need to develop new analytical approaches that improve models and predict impacts of water balance (precipitation inputs minus ET losses) on this labile C pool. It is understood that oxygen isotopic ratios of plant water resemble meteoric water following the isotopic fractionation that occurs by ET. We have shown that this signal is preserved in hexane extracts of bulk plant material, which suggests the potential for accumulated organic matter in soils to be used as a proxy for integrated ecosystem water balance. This is especially relevant as lipids are a compound group with the potential to be preserved in soil. Moving forward, we seek to separate specific plant compounds from bulk plant and soil material that have been identified as abundant and ubiquitous, in an effort to better characterize plant soil atmosphere biophysical relationships. The final product of these efforts will be a new integrated framework for determining causal links between processes occurring above and below ground, to improve guidelines for social and economic development while conserving irreplaceable natural resources.