Modelling hydraulic plasticity of mangroves

Abstract

The hydraulic architecture of plants responds to their water availability, mediating between promoting water flow and providing hydraulic safety against embolism. Sites with a constant supply of water favor plants with large vessel diameters, while in dry conditions, narrower vessels are more advantageous. The characteristics of the vessels are primarily shaped by the species’ adaptation to its preferred habitat. However, physiological plasticity enables individual plants to undergo further adaptations to suit specific sites. Mangroves are constantly exposed to low water potentials and therefore hydraulic properties play a pivotal role. Reevaluating studies on vessel diameter distributions and xylem conductivities, we propose a two-parameter gamma distribution description of the hydraulic system. The shape parameter characterizes the species-specific component, and the rate parameter specifies the particular adaptation of the plant to the site salinity. Based on the Hagen–Poiseuille law, we can estimate the xylem conductivity of the plant. Applying this approach to the established single tree model BETTINA, we show the potential plant damage due to salinity shocks for stylized species with different hydraulic properties. Model results suggest that plants with a vessel diameter distribution similar to Rhizophora spp. have an advantage and grow faster under constant salinity conditions due to higher hydraulic conductivities compared to Avicennia-like diameter distributions. This comes at the cost of a higher hydraulic vulnerability to salinity changes of Rhizophora. This approach provides a mechanistic link between site conditions and the hydraulic properties of plants in terms of their ability to physiologically adjust to the site.