Leveraging plant hydraulics to yield predictive and dynamic plant leaf allocation in vegetation models with climate change

• Published in: Global change biology 2019-12, Vol.25 (12), p.4008-4021
• Main Authors: Trugman, Anna T., Anderegg, Leander D. L., Sperry, John S., Wang, Yujie, Venturas, Martin, Anderegg, William R. L.
• Format: Article
• Language: English
• Subjects: allocation; Allometry; Carbon; Carbon Cycle; Climate Change; Climate models; Computational fluid dynamics; Computer applications; Constraints; ecohydrological equilibrium; Ecosystem; Ecosystem dynamics; Ecosystems; Environment models; Environmental changes; Environmental impact; First principles; Fluid flow; Fluxes; Hydraulics; Leaf area; Leaves; optimization; plant hydraulics; Plant Leaves; Plants; Representations; Uptake; Vegetation; vegetation models; vegetation water demand; Water stress
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.14814

Plant functional traits provide a link in process‐based vegetation models between plant‐level physiology and ecosystem‐level responses. Recent advances in physiological understanding and computational efficiency have allowed for the incorporation of plant hydraulic processes in large‐scale vegetation models. However, a more mechanistic representation of water limitation that determines ecosystem responses to plant water stress necessitates a re‐evaluation of trait‐based constraints for plant carbon allocation, particularly allocation to leaf area. In this review, we examine model representations of plant allocation to leaves, which is often empirically set by plant functional type‐specific allometric relationships. We analyze the evolution of the representation of leaf allocation in models of different scales and complexities. We show the impacts of leaf allocation strategy on plant carbon uptake in the context of recent advancements in modeling hydraulic processes. Finally, we posit that deriving allometry from first principles using mechanistic hydraulic processes is possible and should become standard practice, rather than using prescribed allometries. The representation of allocation as an emergent property of scarce resource constraints is likely to be critical to representing how global change processes impact future ecosystem dynamics and carbon fluxes and may reduce the number of poorly constrained parameters in vegetation models. One important lever plants use to adjust water demand to local water availability is through changing carbon allocation to leaf area relative to water transport tissue area in the stem. This is because leaf area to stem area regulates water demand from leaves relative to supply capacity by the stem. In this review, we examine vegetation model representations of plant allocation to leaves, how allocation impacts mechanistic model‐derived estimates of productivity, and methods for moving forward with representing allocation as an emergent property of scarce resource constraints in trait‐based vegetation models.