2024 Abstracts

Empirical Measurements and Model Representation of Hydraulic Redistribution as a Control on Function of Semiarid Woody Ecosystems


William Pockman1* (pockman@unm.edu), Marcy Litvak1, Yiqi Luo2, Aneesh Chandel2, Hang Duong1, Yu Zhou2


1University of New Mexico, Albuquerque, NM; 2Cornell University, Ithaca, NY


Earth System Model (ESM) projections of ecosystem responses to climate change require knowledge of biomes that vary in climate sensitivity. Drylands influence the trend and interannual variability in global sink strength but are difficult to represent in ESMs. Incorporation of plant-mediated hydraulic redistribution (HR; flow in plant roots from wetter to drier soil) can improve ESM performance in drylands. Researchers combine measurements of sap flow, soil moisture, and ecosystem-scale net ecosystem exchange  (NEE), gross primary production (GPP), and ecosystem respiration Re, and use data assimilation to develop the Terrestrial Ecosystem (TECO) model to address three objectives:

  1. Understand the controls on HR in species and biomes across a range of semi-arid western woodlands/forests. At four Ameriflux sites, supplemental depth profiles of volumetric soil moisture and soil water potential sensors, colocated with measurements of root sap flux capture patterns of HR, the physical factors driving it, and related ecosystem function as HR varies.
  2. Quantify seasonal patterns of HR across dryland species and biomes to determine when HR affects soil moisture dynamics and ecosystem function. Researchers measure HR from lower elevation juniper savanna and pinon-juniper woodlands to higher-elevation ponderosa pine and mixed conifer forests, leveraging data collection at tower sites and supplementing these efforts with additional soil and sap flux measurements.
  3. Scale plant-level patterns in HR to ecosystem-level NEE, GPP and Re in response to precipitation anomalies. Incorporating HR into TECO predicted upward HR with increased shallow soil moisture during dry periods and a corresponding reduction in deep soil moisture. After rainfall, the TECO+HR model predicted downward HR. Introducing HR also predicted noticeable effects on carbon fluxes alleviating the impact of drought, resulting in a predicted 8 to 21% increase in GPP and NPP, and a 5 to 12% rise in Re. These findings highlight the significant role of HR in influencing both soil moisture dynamics and carbon fluxes in an ecosystem.