Morphological Applications in the Physics-Ecology Interface in Dryland Soils

Abstract

The relationship between form and function in dryland soils is multi-scale and multi-disciplinary. Organisms as ecosystem engineers can modify and influence soil physical structure, either directly or indirectly, and this in turn can have cascading consequences to the various ecological functions in the impacted soil system. Despite its importance, however, the causes, mechanisms, and consequences of this feedback, which is in the domain of both soil physics and ecology, all remain open questions. This dissertation uses mathematical morphology and topology to provide mechanistic explanations for feedbacks between soil physical structure and ecological function and processes in dryland soils. Two applications are considered, the first of which is flora: in Chapter 2, I develop an open-source software package at Oak Ridge National Laboratory for the automated digital image analysis of plant root morphology in soil and its associated plant-soil characteristics. In Chapter 3, I apply the software developed in Chapter 2 to spatially integrate plant morphological traits and bulk soil water characteristics, and show species-independent soil water properties, dynamics, and uptake across the plant-soil interface, also known as the rhizosphere. In Chapter 4, I switch my ecological focus to that of fauna, where I characterize biophysical effects on soil crack morphology in a faunally active dryland vertisol in Kenya. I find divergent crack morphologies based on macrofauna-based bioturbation or megaherbivore-based biocompaction. I conclude this dissertation by applying the divergent crack morphologies characterized in Chapter 4 to study their consequence on carbon flux dynamics in the same soil system. I show that constraints from particular crack morphologies, combined with limited soil carbon production, create lower mean flux punctuated by outlier fluxes that are orders of magnitude higher. I also show that mechanical enhancements of CO2 efflux caused by thermal convection are induced by soil crack morphology.