de Melo Silva, L. | Search bioRxiv

bioRxiv2026

Interconduit pit membranes of temperate angiosperms undergo changes in pit membrane thickness and electron density within the final growth ring

O_LIPit membranes play a crucial role in water transport between neighbouring xylem conduits by providing hydraulic safety and flow resistance. While effects of pit membranes thickness on embolism resistance and temporal changes in the ultrastructure of pit membranes have been documented between sapwood and heartwood, these changes are largely unknown within conduits of the current-year. C_LIO_LIWe studied interconduit pit membranes of branches of eight angiosperm species by sampling wood from a temperate forest over four consecutive seasons, focusing on the latest growth ring. We quantified the pit membrane thickness and greyscale intensity (as a proxy for electron density) using transmission electron microscopy and image analysis. C_LIO_LIOur observations showed considerable interspecific variation in changes to pit membrane thickness and electron density. Several species exhibited the thinnest pit membranes and highest electron density at the end of a growing season, while others showed minimal variation over time. Intra-tree variation showed that changes in pit membrane shrinkage and electron density were associated with conduit diameter: pit membranes in wide conduits showed larger modification over time than narrow ones. C_LIO_LIOur results indicate seasonal changes in the structure and chemistry of angiosperm pit membranes, even within the latest growth ring. While their shrinkage might increase resistance to flow, the occurrence of darker pit membranes indicates coating and penetration by polar lipids, affecting the behaviour of gas-liquid interfaces. We speculate that the degree of modification that pit membranes undergo is mechanistically driven by the sap flow rate, and possibly conduit dimensions. C_LI

plant biology↗

bioRxiv2025

The SI compartment model describes embolism spreading in networks of vessels and bordered pits in angiosperm xylem

Plant xylem consists of a network of interconnected vessels, through which water is transported under negative pressure. Filling of vessels with air, or embolism, disturbs this transport process and, in extreme cases, leads to tree mortality. Despite this significance, embolism propagation dynamics are still poorly understood, primarily because xylem is opaque to direct observation. Furthermore, existing models of embolism spreading build excessively on physiological and anatomical parameters, and many misrepresent the inter-vessel pit membrane as a 2D surface. Here, we first extend these physiological models by implementing the pit membrane as a 3D object. Then, we introduce a susceptible-infected (SI) model, a simple stochastic model for tracking spreading through a population, for embolism propagation. After correctly fitting the spreading probability, our SI model reproduces vulnerability curves produced by both the physiological model and empirical data, highlighting that the SI model can address embolism spreading dynamics in plant species, for which detailed physiological data are not available. Furthermore, relating the SI model to the physiological one allows interpreting embolism spreading as a directed percolation process. Elucidating the exact mapping between directed percolation and embolism spreading will likely yield new fundamental insights into the relationships between xylem network architecture and embolism dynamics.

plant biology↗