Evolutionary relationships between drought-related traits and climate shape large hydraulic safety margins in western North American oaks

Quantitative knowledge of xylem physical tolerance limits to dehydration is essential to understanding plant drought tolerance but is lacking in many long-vessel angiosperms. We examine the hypothesis that a fundamental association between sustained xylem water transport and downstream tissue function should select for xylem that avoids embolism in long-vessel trees by quantifying xylem capacity to withstand air entry of western North American oaks (Quercus spp.). Optical visualization showed that 50% of embolism occurs at water potentials below −2.7 MPa in all 19 species, and −6.6 MPa in the most resistant species. By mapping the evolution of xylem vulnerability to embolism onto a fossil-dated phylogeny of the western North American oaks, we found large differences between clades (sections) while closely related species within each clade vary little in their capacity to withstand air entry. Phylogenetic conservatism in xylem physical tolerance, together with a significant correlation between species distributions along rainfall gradients and their dehydration tolerance, suggests that closely related species occupy similar climatic niches and that species' geographic ranges may have shifted along aridity gradients in accordance with their physical tolerance. Such trends, coupled with evolutionary associations between capacity to withstand xylem embolism and other hydraulic-related traits, yield wide margins of safety against embolism in oaks from diverse habitats. Evolved responses of the vascular system to aridity support the embolism avoidance hypothesis and reveal the importance of quantifying plant capacity to withstand xylem embolism for understanding function and biogeography of some of the Northern Hemisphere’s most ecologically and economically important plants.

Templating the morphology of soft microgel assemblies using a nanolithographic 3D-printed membrane

Filter cake formation is the predominant phenomenon limiting the filtration performance of membrane separation processes. However, the filter cake’s behavior at the particle scale, which determines its overall cake behavior, has only recently come into the focus of scientists, leaving open questions about its formation and filtration behavior. The present study contributes to the fundamental understanding of soft filter cakes by analyzing the influence of the porous membrane’s morphology on crystal formation and the compaction behavior of soft filter cakes under filtration conditions. Microfluidic chips with nanolithographic imprinted filter templates were used to trigger the formation of crystalline colloidal filter cakes formed by soft microgels. The soft filter cakes were observed via confocal laser scanning microscopy (CLSM) under dead-end filtration conditions. Colloidal crystal formation in the cake, as well as their compaction behavior, were analyzed by optical visualization and pressure data. For the first time, we show that exposing the soft cake to a crystalline filter template promotes the formation of colloidal crystallites and that soft cakes experience gradient compression during filtration.