Biology subjects

Mayr, S.

Publications and source records attributed to Mayr, S..

4 recordsLinked to original sources

bioRxiv2026

Beyond air-seeding: Dynamic, multiphase interactionsreveal a two-step mechanism of embolism propagation inangiosperm xylem

BackgroundThe mechanism underlying drought-induced embolism in angiosperm xylem has been attributed to air-seeding. This concept describes the bulk flow of gas from embolised to neighbouring conduits through the penetration of gas-liquid menisci across pores in interconduit pit membranes. While there is compelling evidence for the spatial propagation of embolism, air-seeding rests on various simplifying assumptions. Among others, air-seeding presumes that xylem sap has physical properties comparable to pure water, that pit membranes can be approximated as structures with simple pores, and that embolism occurs whenever a gas-liquid interface crosses a pit membrane. ScopeRecent experimental and theoretical work demonstrates that the biophysical conditions and processes governing gas-liquid interactions at interconduit pit membranes are fundamentally more dynamic and complex than assumed by air-seeding. These phenomena include: (1) gas movement through constriction pore networks, (2) insoluble, polar lipids at conduit surfaces and interfaces, (3) dynamic surface tension of xylem sap that depends on the local packing density of interfacial lipids, (4) bubble snap-off dynamics within pit membranes, (5) surfactant-stabilized nanobubbles in sap that is oversaturated with dissolved gas, and (6) electrostatic interactions between charged interfaces. Importantly, embolism propagation involves bubble generation and embolism formation as distinct, temporarily and spatially separated processes. Embolism formation occurs when nanobubbles become unstable, whereas nanobubbles below critical stability thresholds can remain stable in sap-filled conduits. ConclusionsTogether, these findings reconfirm that pit membranes function as safety valves enabling water transport according to the cohesion-tension theory, and provide mechanistic insights into embolism propagation. They address the question why plants do not suffer constant embolism formation despite negative xylem pressures. We conclude that a revised framework explicitly accounting for the 3D structure of pit membranes, and multiphase, dynamic processes operating within them are required to explain the biophysics underlying water transport and embolism resistance in angiosperm xylem.

plant biology↗

bioRxiv2026

The coordination between xylem and bark hydraulics in temperate Rosaceae species

Xylem and bark properties influence tree growth and drought resistance, yet their functional coordination and their environmental drivers remain unclear. We assessed xylem-bark coordination in branches of eight temperate woody Rosaceae species spanning different ecological preferences. We quantified xylem hydraulic efficiency and safety alongside bark traits governing permeability, hygroscopic water exchange, water storage, and anatomy, and evaluated phylogenetic signal and climatic associations. Bark water vapor conductance (Gbark) increased with maximum xylem hydraulic conductivity (Kh) and with xylem water potential at 50% loss of conductivity (P50), indicating species with more efficient but more embolism-vulnerable xylem developed more permeable bark. Species with higher Gbark showed reduced hygroscopic absorption time, consistent with faster rehydration from atmospheric water vapor. Both Gbark and P50 were phylogenetically conserved and covaried with climatic factors, namely air temperature, vapor pressure deficit (VPD), and isothermality. Species from warmer, high-VPD climates with greater diurnal temperature variability combined higher bark permeability with more vulnerable xylem, implying a shift from embolism avoidance to embolism tolerance strategies. Overall, xylem and bark hydraulics in Rosaceae evolved in concert along diurnal and annual gradients of evaporative demand, showing that drought resistance in woody angiosperms cannot be understood without considering bark traits alongside xylem function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/730605v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@449b24org.highwire.dtl.DTLVardef@2586c8org.highwire.dtl.DTLVardef@1b3dc8dorg.highwire.dtl.DTLVardef@154adda_HPS_FORMAT_FIGEXP M_FIG C_FIG Caption: This study shows that xylem and bark in Rosaceae species form an integrated functional system in which xylem hydraulic safety, efficiency, and bark permeability are jointly tuned along diurnal and annual gradients of air temperature and evaporative demand.

plant biology↗

bioRxiv2025

Unravelling the intraspecific variation in drought responses in seedlings of European black pine (Pinus nigra J.F. Arnold)

O_LIUnderstanding intraspecific variation in drought tolerance is essential for predicting the adaptive capacity of forest species under climate change. Yet, the molecular basis of this variation remains poorly understood in ecologically and economically important conifers. C_LIO_LIWe integrated high-throughput phenotyping with metabolomics and transcriptomics under standardized soil drying to investigate drought responses across nine climatically distinct provenances of the conifer Pinus nigra. We tested whether drought tolerance--measured as decline in maximum quantum yield of the photosystem II (Fv/Fm)--varies among provenances, follows a climatic cline, and involves trade-off with growth. To identify the underlying molecular basis, we performed metabolomics and transcriptomics in four provenances representing contrasting drought tolerance. C_LIO_LIDrought tolerance varied significantly among provenances and was decoupled from growth, yet showed no differentiation along the climatic cline. Drought tolerant provenances differed from sensitive ones in both constitutive and drought-induced levels of flavonoid and diterpene metabolites. Transcriptomic profiles further highlighted provenance-specific differences in gene expression related to flavonoids. C_LIO_LIOur results demonstrate the utility of integrating automated phenotyping with molecular profiling to uncover the metabolic basis of drought adaptation, laying the groundwork for targeted studies on metabolite function and tolerance strategies in non-model conifers. C_LI

plant biology↗

bioRxiv2022

Impact of freeze-thaw-induced pit aspiration on stem water transport in a subalpine conifer (Abies veitchii)

During winter, subalpine conifers experience frequent freeze-thaw cycles in stem xylem, which may cause embolism and pit aspiration due to increased water volume during the sap to ice transition. This study examined the occurrence and ecological impacts of a combination of freeze-thaw-induced pit aspiration and embolism. In subalpine Abies veitchii trees, the fraction of closed pits and embolized tracheids as well as conductivity losses were measured to examine pit aspiration and its effects, triggered by natural and artificial stem freezing. When trees incurred mild drought stress in February and early March, 70% to 80% of stem conductivity was lost. Cryo-scanning electron microscopy indicated <20% embolized tracheids but [~]90% closed pits. Severe drought stress in late March caused 96 {+/-} 1.2% (mean {+/-} SE) loss of stem conductivity, while the fraction of embolized tracheids increased to 64 {+/-} 6.6%, and aspirated pit fraction decreased to 23 {+/-} 5.6%. Experimental freeze-thaw cycles also induced from 7.1 {+/-} 0.89% to 49 {+/-} 10% pit aspiration, and the fraction of closed pits was positively correlated to the percent loss of stem hydraulic conductivity. Results indicated that freezing-induced pit aspiration is an important factor for stem xylem dysfunction under mild drought. Upon severe drought in winter, stem water transport is predominantly inhibited by xylem embolism.

plant biology↗