An Ecophysiological Perspective of Hydraulic Redistribution: Feedbacks on Soil, Fungal, and Root Morphologies

Authors

Alex Redlins¹* (redlinsa@oregonstate.edu), Pamela Sullivan¹, Kamini Singha², Holly Barnard³, Emily Graham⁴, Rahila Yilangai³

Institutions

¹Oregon State University–Corvallis, OR; ²Colorado School of Mines, Golden, CO; ³University of Colorado–Boulder, CO; ⁴Pacific Northwest National Laboratory, Richland, WA

Abstract

Hydraulic redistribution is the passive movement of water within the soil profile from wetter areas to drier areas via biological pathways such as roots and fungal hyphae. Hydraulic redistribution of soil water into the upper soil horizons may have important implications on root morphology and soil biota, particularly in water-limited environments such as those of the western United States. The reduced rates of soil drying through periods of drought, which results from the passive regulation of near-surface soil water, may limit fine root desiccation, reduce root embolism, increase the lifespan of roots, enhance overall rooting architecture, and help to maintain important mycorrhizal interactions. This project will explore the dynamic relationship between the rooting, fungal, and soil morphologies under Douglas-fir (Pseudotsuga menziesii) across different water availability regimes and seek to understand how these morphologies influence the magnitude, timing, and flow paths of water redistribution to near-surface soils. To achieve this, the team will combine a multiyear greenhouse experiment with a field study at H. J. Andrews Experimental Forest on two adjacent hillslopes, which have been shown to exhibit two contrasting hydraulic redistribution regimes as demonstrated through previous study of the site. Using microcomputed tomography of soil cores, researchers will be able to characterize the spatial distribution of soil pores and derive a detailed understanding of soil morphological characteristics. This will be combined with reconstruction of rooting architecture in the greenhouse experiment through destructive sampling of pots throughout the course of the experiment and in the field through existing methods of characterizing root abundances in soils. Furthermore, the quantification of fungal and mycorrhizal concentrations throughout the rooting profile will be obtained through hyphal-length analysis. The identification and quantification of hydraulically redistributed water will be measured by building on existing methods of sap-flow and water content measurements, with the deployment of new geophysical techniques for the detailed mapping of the magnitude and flow paths of near-surface water. Taken together, these data will help to clarify the complex feedbacks between subsurface hydrology, rooting and fungal behavior, and soil morphological properties.