Water potential as a master variable for atmosphere-soil trace gas exchange in arid and semiarid ecosystems
Abstract
© 2017 Walter de Gruyter GmbH, Berlin/Boston. All rights reserved. Soil water status strongly affects qualitative and quantitative aspects of soil- atmosphere trace gas exchange. Soil water status is most often expressed in terms of gravimetric water contents, which can be particularly useful when translated to gas filled pore space. Gas filled pore space has predictive value for both gas transport rates and the types of processes involved in gas production and consumption. However, water potential offers deeper insights that reflect the physiological responses of cells, while also providing a basis for comparing activities among different soil types and across wetting and drying events. Nonetheless, relatively few studies have incorporated water potential measurements with analyses of trace gas fluxes. Results for atmospheric methane uptake suggest similar sensitivities to water potential for arid soils and forest soils, with strong inhibition below -0.5MPa. Atmospheric CO uptake in forest soils shows sensitivities similar to those of methane uptake, but recent evidence suggests that CO oxidizers in arid and saline soils might maintain activity at remarkably low potentials. Advances in sensor design should facilitate much more extensive analyses of water potential, more mechanistic models of trace gas exchange, and a better understanding of the controls trace gas dynamics.