Exploring the Influence of Dual Stresses of High Salinity and High Vapor Pressure Deficits on Water Transport in Mangroves

Authors

Ashley M. Matheny¹* (ashley.matheny@jsg.utexas.edu), Maria Ulatowski¹, Annalisa Molini², Matteo Detto³, Chonggang Xu⁴, Tim Shanahan¹

Institutions

¹University of Texas–Austin, TX; ²Tulane University, New Orleans, LA; ³Princeton University, Princeton, NJ; ⁴Los Alamos National Laboratory, Los Alamos, NM

URLs

• http://www.jsg.utexas.edu/matheny/halophyte-hydrodynamics/

Abstract

Mangroves grow along coastlines and intertidal zones and are therefore very rarely limited by water availability. However, during dry periods, these ecosystems behave more similarly to semi-arid ecosystems than like well-watered forests. Mangroves likewise provide a critical carbon sink sequestering carbon at a rate disproportionate to the ecosystem extents. Modeling the water and carbon dynamics of mangrove forests is a critical task for developing robust models of coastal climate processes, particularly in the face of sea level rise and disruptions to local hydroclimates and therefore freshwater inputs.

Here, researchers present results of a combined greenhouse and field study of responses of the mangrove species Avicennia germinans, Avicennia marina, and Rhizophora mangle to fluctuating humidity and salinity conditions. Water uptake in plants is limited by both water supply within the root zone and water demand by the atmosphere at the leaves. For most mangroves, water availability to roots is limited not by the presence of water, but by salinity concentration and the time and energy necessary for the development of the osmotic potential gradient, which drives water uptake. Researchers studied sap flux, stem and leaf water potential, stem hydraulic conductivity, stomatal conductance, and net photosynthetic assimilation of carbon for each of the three species in order to assess responses to high vapor pressure deficits and high salinities. Observations were also used to create species-specific plant hydraulics parameters for use with the FETCH plant hydrodynamics model, which researchers have augmented to mechanistically include osmoregulation of water uptake by halophytes. FETCH-osmo is designed to promote analysis of mangrove forest function across both humidity and salinity gradients, which are predicted to change in response to disturbances such as sea level rise, precipitation variability, inundation frequency, and increased atmospheric carbon dioxide. Ultimately, the new FETCH-osmo model will be integrated into the DOE’s functionally assembled terrestrial simulator (FATES) within E3SM.