Linking Field Experiments and Modeling to Understand the Role of Hydraulic Redistribution in Temperate Forests
Authors
Elin Jacobs1* (ekarlsso@purdue.edu), Zoe Cardon2, Jeffrey Dukes3, Yilin Fang4, Theresa Hudson1, Indira Paudel3, Lisa Welp-Smith1
Institutions
1Purdue University, West Lafayette, IN; 2Marine Biology Laboratory, Woods Hole, MA; 3Carnegie Institute for Science, Palo Alto, CA; 4Earth System Science Division, Pacific Northwest National Laboratory, Richland, WA
Abstract
Plant-mediated hydraulic redistribution (HR) may play a significant role in maintaining photosynthesis and transpiration rates during periods of drought. Climate projections suggest that warmer conditions will consistently increase water stress during the growing season, which may exacerbate droughts and increase the importance of HR in buffering periods of water limitation. However, these processes are currently not well constrained in Earth system models which could be a source of the well-known uncertainty in simulations of soil moisture states and of water and carbon fluxes.
Researchers use field experiments to better understand the prevalence and magnitude of HR across tree species, tree sizes, and drought durations in three temperate forest species (Juglans nigra, Quercus rubra and Acer saccharum), representing contrasting hydraulic strategies, by measuring soil and plant hydrologic and hydraulic properties and fluxes. Trees are instrumented with sap flow probes at three locations ranging from the roots to the lowest branch, psychrometers and water content probes. To facilitate the soil moisture gradient that is necessary for HR to take place, 50% of the trees are equipped with plastic skirts that prevent water from replenishing upper soil layers.
Simultaneously, researchers use model sensitivity experiments to explore the hypothesized water resource competition between nighttime stomatal conductance, recharge of plant-water storage and hydraulic redistribution. Better understanding of this partitioning and its influence on fluxes is a key first step to improving model parameterizations of HR. Researchers use two models that couple with the E3SM land model (ELM); the parameter-rich FATES-HYDRO hydrodynamics model and ELM with a new, simpler, plant hydraulic stress (PHS) representation. Researchers provide an overview of the field and model experimental designs and of the results and lessons learned available at this early point in the project.