Reich et al. (2025) Beyond optimality: Dryland ecosystems infrequently use water efficiently for carbon gain

Identification

• Journal: Agricultural and Forest Meteorology
• Year: 2025
• Date: 2025-12-26
• Authors: E.G. Reich, K. Samuels-Crow, JB Bradford, M. Litvak, D.R. Schlaepfer, K. Ogle
• DOI: 10.1016/j.agrformet.2025.110996

Research Groups

• School of Informatics, Computing and Cyber Systems, Northern Arizona University, Flagstaff, AZ, USA
• Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
• United States Geological Survey, Northwest Climate Adaptation Science Center, Corvallis, OR, USA
• United States Geological Survey, Southwest Biological Science Center, Flagstaff, AZ, USA
• Department of Biology, University of New Mexico, Albuquerque, NM, USA
• Center for Adaptable Western Landscapes, Northern Arizona University, Flagstaff, AZ, USA
• Center of Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA

Short Summary

This study investigates the applicability of optimality theory, which posits that plants maximize carbon gain per unit water lost (WUE scales with VPD^k, k=½), in dryland ecosystems. It reveals that dryland plant water-use efficiency often deviates from optimal behavior, particularly under arid conditions or low soil moisture, underscoring the necessity for dynamic representations of plant water-use strategies.

Objective

• To determine how the relationship between ecosystem-level water-use efficiency (WUE) and vapor pressure deficit (VPD) in dryland ecosystems compares to expectations based on optimality theory, specifically examining if the sensitivity (k) of WUE to VPD aligns with the theoretical optimal value of ½.

Study Configuration

• Spatial Scale: Seven flux tower sites along an aridity gradient in New Mexico, USA.
• Temporal Scale: Daily and seasonal variability in the sensitivity of WUE to VPD (kDynamic).

Methodology and Data

• Models used: Dynamic Evapotranspiration Partitioning Approach for Rapid Timescales (DEPART) integrated with a stochastic antecedent model.
• Data sources: Ecosystem-level flux data from seven flux tower sites.

Main Results

• Optimality theory, assuming k = ½, is not consistently appropriate for describing plant water-use strategies in dryland ecosystems.
• The estimated net sensitivity of WUE to VPD (kDynamic) frequently deviates from the theoretical optimal value of ½.
• These deviations are most pronounced at more arid sites or during periods of low soil moisture.
• At less arid, higher elevation sites, kDynamic aligns with optimality theory only at moderate VPD levels, but not at high VPD.
• kDynamic exhibits significant daily and seasonal variability, indicating highly dynamic stomatal behavior in dryland plants.

Contributions

• Challenges the widespread assumption of optimality theory (k = ½) for plant water-use in dryland ecosystems, demonstrating that these systems infrequently use water efficiently for carbon gain as predicted.
• Provides empirical evidence for the highly dynamic nature of stomatal behavior and WUE sensitivity to VPD in drylands, varying across spatial aridity gradients and temporal scales.
• Emphasizes the critical need for incorporating dynamic representations of plant water-use strategies in time and space to improve the accuracy of large-scale estimates of plant water use and carbon cycling.

Funding

No funding information was provided in the excerpt.

Citation

@article{Reich2025Beyond,
  author = {Reich, E.G. and Samuels-Crow, K. and Bradford, JB and Litvak, M. and Schlaepfer, D.R. and Ogle, K.},
  title = {Beyond optimality: Dryland ecosystems infrequently use water efficiently for carbon gain},
  journal = {Agricultural and Forest Meteorology},
  year = {2025},
  doi = {10.1016/j.agrformet.2025.110996},
  url = {https://doi.org/10.1016/j.agrformet.2025.110996}
}