Biology subjects

Meischner, M.

Publications and source records attributed to Meischner, M..

6 recordsLinked to original sources

bioRxiv2026

13CO2 pulse labelling reveals species-specific alterations in carbon allocation and volatile organic compound emissions under heat stress

Temperate forests increasingly face extreme air temperature, but plant physiological responses, particularly alterations in carbon allocation or protection via volatile organic compound (VOC) emissions, remain poorly understood. We pulse-labelled well-watered saplings of Fagus sylvatica and Pseudotsuga menziesii in a controlled heat stress experiment with 13CO2 to quantify heat-induced shifts in CO2, VOC and C pool exchange, specifically analyzing compound-specific {delta}13C of terpenoids, water-soluble organic matter (WSOM) and dark respiration. Under heat stress, up to 50% of fresh assimilates were directed to maintenance respiration and 1-2% to VOC emissions, while net assimilation and water use efficiency decreased by 50-75% in both species. Heat directly affected metabolic processes and reduced turnover rates of fresh assimilates in F. sylvatica, but accelerated them in P. menziesii. Strong 13C labelling of some compounds, particularly acyclic ones, suggested increased de novo synthesis of specific terpenoids for heat stress protection. By tracing the fate of recently assimilated 13CO2 we demonstrate that heat stress reduces net carbon uptake and water use efficiency, disrupts turnover of C pools and increases carbon loss via respiration and de novo synthesis of specific VOCs, potentially diminishing net carbon uptake of forests under future heat extremes.

plant biology↗

bioRxiv2026

Early warning indicators for heat-induced mortality in temperate tree saplings

{middle dot} Globally, forest ecosystems face widespread mortality events. However, the independent impacts of distinct stressors, such as heat stress vs edaphic drought, remain poorly understood and physiological early warning indicators for tree mortality are urgently required. {middle dot} We exposed well-watered saplings of Fagus sylvatica, Pseudotsuga menziesii and Picea abies to summer heat waves and subsequent natural winter-desiccation. Physiological parameters (e.g. gas exchange, water uptake velocity via 2H labelling, and volatile organic compound emissions) were monitored throughout the growing season and survival was assessed regularly until subsequent spring to capture immediate and delayed mortality as a consequence of legacy effects. {middle dot} Heat exposure without soil water deficit, followed by winter desiccation, triggered species-specific mortality rates (51.8% F. sylvatica, 48.2% P. abies, 16.9% P. menziesii), with P. abies exhibiting significantly faster mortality response than the other species. Reduced water uptake, lower stomatal conductance, impaired photosynthetic efficiency, and altered VOC emissions distinguished non-surviving from surviving saplings months before visible damage in all three species. {middle dot} Heat stress drives mortality independent of edaphic drought, with sub-lethal physiological indicators detectable up to 10 months before visual signs. These early warning indicators could enable damage detection before lethal thresholds are crossed, offering new strategies for mitigating climate change-driven forest decline.

ecology↗

bioRxiv2026

The rhizosphere of Picea abies is a hotspot of terpenoid production

Forest soils are an important source of volatile organic compounds (VOCs), yet little is known about how different tree species influence soil VOC emissions and the role of rhizosphere processes in mediating VOC release form roots. We analysed soil VOC emissions from the soil surface and bulk soil as well as from roots with intact rhizosphere and washed roots of Picea abies and Fagus sylvatica. Tree saplings were grown on natural forest soil, and VOC emissions and gas exchange of soils and roots were measured under controlled conditions using online gas analysers integrated into an automated system. To assess the contribution of rhizosphere soil and microbial communities to root VOC emissions, roots were analysed (a) without washing, preserving the rhizosphere, (b) water-washed, and (c) ethanol-washed (70 vol%) to minimize microbial contributions. Species-specific VOC emission patterns were observed in both soils and roots. P. abies showed higher total emission rates and a more diverse, terpenoid-rich VOC profile dominated by -pinene, {beta}-pinene, {beta}-myrcene, and -phellandrene than F. sylvatica. Notably, these differences were evident not only at the soil surface but also in root and litter free bulk soil. Root washing further revealed that the rhizosphere is a hotspot of terpenoid production in P. abies, with significantly higher monoterpenoid emissions from unwashed roots than from water or ethanol-washed roots. This study demonstrates how tree species shape net soil VOC emissions, potentially leading to cascading effects on atmospheric VOC concentrations, and highlights the importance of the rhizosphere in regulating belowground VOC production.

plant biology↗

bioRxiv2026

Synergistic effect of heat and drought on leaf VOC emissions and root exudates in Norway spruce saplings

Compound droughts, i.e. the co-occurrences of heat and drought, represent a serious challenge for temperate forest trees leading to significant losses in forest biomass. We studied the physiological response of Norway spruce (Picea abies) saplings to heat and drought individually, and in combination. Continuous measurements of leaf gas exchange and VOC emission allowed us to identify fast-response reactions, while discrete VOC and root exudate samplings added qualitative information on compositional changes. Additionally, we used 13CO2 and 2H2O label pulses to investigate C-allocation and root water uptake in response to stress. Heat as well as drought reduced assimilation rates in the saplings, whereas transpiration, leaf VOC emission and root exudation rates increased in response to heat. Drought alone increased VOC emission but decreased exudation rates. Combined heat and drought triggered an amplified response in both processes despite negative net CO2 assimilation rates. Label incorporation showed compromised water uptake capacity of drought-stressed plants and illustrated de novo C-allocation to VOC emission and root exudates. The results point at the high susceptibility of Norway spruce saplings to drought and heat. Combined stress resulted in synergistic responses in VOC emissions and root exudates, showing the detrimental effect of compound droughts on Norway spruce. HighlightIn this study, we found synergistic effects of heat and drought on carbon losses from leaf VOC emission and root exudates despite negative assimilation rates in Norway spruce saplings.

plant biology↗

bioRxiv2025

Eavesdropping roots: Fagus sylvatica detects belowground stress signals from conspecific and heterospecific (Picea abies) neighbors, triggering increased shoot VOC emissions

O_LIVolatile organic compounds (VOCs) facilitate aboveground plant communication, but belowground signaling remains less understood. C_LIO_LIThis study explored root-root interactions between Picea abies and Fagus sylvatica saplings in monospecific (Fagus-Fagus) and heterospecific (Picea-Fagus) pairs (n=6), excluding shoot-level VOC communication. Sender plants were treated with jasmonic acid to simulate herbivory and labeled with 13CO2 and 15NH4NO3 to trace nutrient transfer in a split-root design. VOC emissions and gas exchange were measured over ten days using PTR-TOF-MS and 13CO2-spectroscopy and 13C and 15N were analyzed in roots and shoots via EA-IRMS. C_LIO_LIOur findings reveal, that (i) JA treatment induced strong de novo terpenoid emissions from P. abies and enhanced emissions of oxygenated VOCs and benzenoids from F. sylvatica, (ii) F. sylvatica receiver plants responded similarly to JA-treated neighbors, indicating belowground signaling, and (iii) responses of receiver plants were more pronounced in the heterospecific treatment. Furthermore, formic acid emissions from soils increased following JA treatment, suggesting altered soil microbial activity. Isotopic analysis revealed C exudation into the rhizosphere and N transfer to receiver plants. C_LIO_LIThese results suggest that belowground signaling enables early priming of herbivore-induced defenses in neighboring plants, and that the response intensity is modulated by species identity. C_LI

plant biology↗

bioRxiv2025

Chiral monoterpene dynamics of shoots and roots of Norway spruce in response to drought

Although chiral monoterpenes emitted by plants above- and belowground shape the chemical landscape of many ecosystems, their biosynthesis and emissions, especially in response to drought, are poorly understood. We imposed a 6-week drought on two-year old, potted saplings of Norway spruce and analysed chiral monoterpene emissions and tissue concentrations from needles and roots. Isotopically labelled pyruvate was used to compare tissue-specific contributions of de novo synthesis to chiral monoterpene concentrations. While de novo synthesis of (-)--pinene and both enantiomers of limonene was apparent in needle emissions, no label was incorporated in roots. Drought reduced chiral monoterpene emissions to 30% of control levels, but increased needle and root tissue concentrations by 150 and 230%, respectively. Aboveground monoterpene concentrations were dominated by (-)-limonene, whereas belowground concentrations mainly consisted of the (-)-enantiomers of -pinene, {beta}-pinene, {beta}-phellandrene and camphene. Chiral composition in needles shifted in response to drought but remained stable in roots. We conclude that chiral monoterpene composition is tissue-specific and likely related to tissue-specific functioning. Instead of being passively emitted from storage pools, our results suggest active control mechanisms regulating chiral monoterpene emissions under drought conditions. Our findings imply important ramifications for understanding the regulation of emissions in relation to storage pools and plant-environmental interactions. Summary StatementEmissions of chiral monoterpenes and their composition is tissue-specific and regulated independent from storage pools in Picea abies. Chiral monoterpene ratios shift aboveground in response to drought, but are not affected belowground.

plant biology↗