Reviews and syntheses: on the roles trees play in building and plumbing the critical zone
Year: 2017
Type: article
Abstract: . Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. The hypotheses are roughly divided into those about the architecture (building) and those about the water (plumbing) in the CZ, but the two functions are intertwined. Depending upon one's disciplinary background, many of the nine hypotheses listed below may appear obviously true or obviously false. (1) Tree roots can only physically penetrate and biogeochemically comminute the immobile substrate underlying mobile soil where that underlying substrate is fractured or pre-weathered. (2) In settings where the thickness of weathered material, H, is large, trees primarily shape the CZ through biogeochemical reactions within the rooting zone. (3) In forested uplands, the thickness of mobile soil, h, can evolve toward a steady state because of feedbacks related to root disruption and tree throw. (4) In settings where h ≪ H and the rates of uplift and erosion are low, the uptake of phosphorus into trees is buffered by the fine-grained fraction of the soil, and the ultimate source of this phosphorus is dust. (5) In settings of limited water availability, trees maintain the highest length density of functional roots at depths where water can be extracted over most of the growing season with the least amount of energy expenditure. (6) Trees grow the majority of their roots in the zone where the most growth-limiting resource is abundant, but they also grow roots at other depths to forage for other resources and to hydraulically redistribute those resources to depths where they can be taken up more efficiently. (7) Trees rely on matrix water in the unsaturated zone that at times may have an isotopic composition distinct from the gravity-drained water that transits from the hillslope to groundwater and streamflow. (8) Mycorrhizal fungi can use matrix water directly, but trees can only use this water by accessing it indirectly through the fungi. (9) Even trees growing well above the valley floor of a catchment can directly affect stream chemistry where changes in permeability near the rooting zone promote intermittent zones of water saturation and downslope flow of water to the stream. By testing these nine hypotheses, we will generate important new cross-disciplinary insights that advance CZ science.
Source: Biogeosciences
Institutions: Pennsylvania State University, Institute of Arctic and Alpine Research, University of Colorado Boulder, University of California, Berkeley, Idaho State University, Hartwick College, University of Minnesota, University of Arizona, Wayne State University, University of Oregon, University of Nevada, Reno, University of California, Santa Barbara, University of Saskatchewan, Cary Institute of Ecosystem Studies
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDG: Life on land
Open Access status: gold
Estimated APC paid: $1,628
Awards: EAR-PF:Seasonal Variation in Suspended Sediment Source and Chemistry in a Shale Watershed, SAVI: Crossing the Boundaries of Critical Zone Science with a Virtual Institute, LINKING TOPOGRAPHIC VARIATION IN BELOWGROUND C PROCESSES WITH HYDROLOGICAL PROCESSES TO IMPROVE EARTH SYSTEM MODELS, Reynolds Creek Carbon Critical Zone Observatory, Transformative Behavior of Energy, Water and Carbon in the Critical Zone II: Interactions between Long- and Short-term Processes that Control Delivery of Critical Zone Services, EAR-PF Cracking the Critical Zone: Tree roots in fractures and a proposed mechanistic soil production function, Using the Susquehanna - Shale Hills CZO to Project from the Geological Past to the Anthropocene Future, G7920240368, CAREER: Ecohydrological controls on land-atmosphere interactions in water-limited ecosystems: a framework for education and research
OpenAlex ID: W2594748282