Biology subjects

Plavcova, L.

Publications and source records attributed to Plavcova, L..

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

Stem photosynthesis is coordinated with seasonal growth activity in two temperate tree species

Woody stems conduct both photosynthetic assimilation and respiration. The two processes work in concert, as stem photosynthesis helps refix CO2 released by stem respiration, thereby increasing carbon-use efficiency and generating a local pool of non-structural carbohydrates supporting cambial growth and stem hydraulic function. Despite its importance, little is known about seasonal variation in stem photosynthesis and the factors underlying its activity throughout the season. To fill this gap, we measured stem gas exchange together with growth activity, water status and photosynthetic pigment contents in two temperate species, Acer platanoides L. and Prunus avium L., over the season. In both species, gross photosynthetic rates (Pg) and dark respiration (Rd) changed significantly over the season in a similar pattern, indicating strong coordination between the two processes. Both Pg and Rd reached the highest values in May, during the period of rapid leaf expansion and secondary growth, and declined later in the growing season. At each measurement date, Rd exceeded Pg, resulting in a net CO2 efflux from the stems. The seasonal changes in Pg and Rd translated into seasonal variability in relative refixation of CO2, ranging from 3 to 59% and gradually decreasing towards the end of the season. Additionally, the Pg corresponded with the tissue hydration and increased significantly with increasing stem water potential. In contrast, total chlorophyll content showed less pronounced seasonal variation and thus explained substantially lower seasonal variability in Pg, except for the chlorophyll a/b ratio, which changed dynamically over the season and reached a minimum during the peak of the growing season. Overall, our results reveal that stem photosynthesis varies seasonally in accord with stem growth and water status, while the chlorophyll content has a lower impact on the seasonal changes. These findings are important for our understanding of the carbon relations of trees.

plant biology↗

bioRxiv2025

When parasites bite hardest: mistletoe effects on oak radial growth peak near climatic optima

Hemiparasitic mistletoes can alter host water and carbon balance, but their impact on tree growth is expected to vary with phenology, microclimate and stand context. We asked whether the yellow mistletoe Loranthus europaeus shifts the timing or reduces the magnitude of radial growth in Quercus robur, and whether any penalty is strongest near climatic optima for host growth. We instrumented 34 mature oaks across age (young, old), canopy position (solitary, closed-canopy), and infection (infected, non-infected) with point dendrometers at 15-minute intervals for four growing seasons (2020-2023). Air and soil temperatures and soil moisture were logged concurrently. We derived growth phenology, difference curves (non-infected minus infected), monthly climate-growth correlations, and response surfaces in temperature- moisture space. Growth phenology was consistent among years: onset around day-of-year 120-140, peak 150-220, cessation 250-270. Mistletoe did not shift onset or cessation but reduced growth amplitude, especially in high-growth years and solitary, well-lit trees. Suppression was greatest near climatic optima ({approx}10-18 {degrees}C with adequate soil moisture) and diminished when conditions were suboptimal (hot and dry or cold and wet), so infected and non-infected converged. Short-term climate-growth relationships were similar across infection status: temperature effects were negative during the main season, whereas soil moisture effects were positive. Young, solitary, non-infected trees responded more to mid-summer moisture than infected trees, consistent with infection shifting hosts from resource-tracking to stress-limited growth under exposure. Joint temperature-moisture response surfaces for infected versus non-infected trees were highly similar, indicating that mistletoe reduces growth magnitude, not niche. Our results identify the environmental window in which host-parasite competition bites hardest and provide a baseline for forecasting parasite impacts under shifting temperature and moisture regimes. Because the largest penalties arise near growth optima, the frequency of cool, moist periods may modulate impacts at the stand scale, particularly for solitary oaks at woodland-grassland ecotones. Integrating fine-scale growth with microclimate clarifies when hemiparasites depress performance and why effects vary across years, sites and canopy contexts. Results underscore the value of continuous dendrometer records for quantifying parasite impacts.

ecology↗

bioRxiv2024

Thermal acclimation of stem respiration reduces global carbon burden

Stem respiration is a key driver of carbon flux from ecosystems to the atmosphere, yet its response to global warming remains poorly constrained. In particular it has been proposed that stem respiration acclimates to changing temperatures, which could have large implications for carbon cycling under climate change, but no theory exists to predict acclimated respiration rates. Here, we hypothesized that stem respiration is physiologically linked to transpiration in order to maintain hydraulic continuity. We then use that linkage, combined with Eco-evolutionary optimality theory, to develop a theoretical prediction of the temperature sensitivity of both acclimated and instantaneous stem respiration. Leveraging an extensive global dataset, we observe temperature sensitivities of stem respiration across geographical and seasonal variations that are consistent with this prediction. Our findings reveal that stem respiration contributes approximately a quarter of the global above-ground auto-trophic respiration, with an estimated annual emission of around 11.20 {+/-} 5.88 Pg C--comparable to total anthropogenic emissions. Importantly, incorporating thermal acclimation of stem respiration into projections significantly reduces predicted land ecosystem carbon emissions by 4.41 and 9.56 Pg C under the SSP126 and SSP585 scenarios, respectively, for the 21st century.

ecology↗