Biology subjects

Kahl, A.

Publications and source records attributed to Kahl, A..

7 recordsLinked to original sources

bioRxiv2026

Stomatal sensitivity to VPD across 38 tree species reflects past drought responses but is little explained by stomatal and leaf economic traits

Climate change is exposing trees to rising atmospheric water demand. Because stomata regulate plant water loss, understanding stomatal behaviour is critical. However, few comparative studies examine species-specific stomatal responses to atmospheric demand. Here, we quantify stomatal behaviour in 38 temperate tree species (27 broadleaved, 11 conifers) in a German research arboretum during a warm summer without soil drought. We measured the diurnal stomatal conductance (gs) of 787 leaves and modelled gs species-specific responses to leaf-to-air vapour pressure deficit (VPDL). Four descriptors of the gs-VPDL relationship were derived: maximum stomatal conductance (gmax), the VPDL that maximises gs, the VPDL associated with a 50% reduction in gs, and the stomatal closure rate. We relate these metrics to drought-induced shifts of carbon isotope ratios and to leaf functional traits. Large variation in stomatal behaviour exists, ranging from early-closure to VPDL-tolerant strategies. Species maintaining gs at higher VPDL also show weaker physiological responses to past drought. gmax is partly explained by leaf economic traits; other gs-VPDL descriptors are not related to stomatal anatomy and leaf economy. Our interspecific comparison reveals substantial variation in stomatal responses to atmospheric demand that is relevant to drought responses, but cannot be readily inferred from commonly measured leaf traits.

ecology↗

bioRxiv2025

Above- and below-ground trait coordination across 90 angiosperm and gymnosperm tree species

Quantifying the variation in plant traits reveals the trade-offs involved in plant ecological strategies and is fundamental to understanding underlying plant fitness mechanisms. Thus, the ecological success of plant species in a certain habitat may depend on the coordinated performance of both leaves and roots. However, despite the growing interest in trait variation, it is still uncertain i) to what extent the leaf economics spectrum (LES) and root economics space (RES) hold across locally coexisting tree species and ii) whether leaf and fine-root traits are correlated. In a research arboretum, we simultaneously measured eight key traits in leaves and fine-roots on 270 individuals belonging to 90 tree species, encompassing both angiosperm and gymnosperm species. We find varied plant resource strategies associated with leaves and fine-roots for angiosperms and gymnosperms. We observe a clear LES for gymnosperms and a clear RES for angiosperms. Our results support the existence of a correlation between analogous leaf and fine-root traits across all species. However, varying trait coordination across clades indicates varying resource acquisition strategies above- and belowground, highlighting the need to consider large-scale phylogenetic relatedness to better understand plant fitness.

ecology↗

bioRxiv2024

Functional traits explain growth resistance to successive hotter droughts across a wide set of common and future tree species in Europe

O_LIIn many regions worldwide, forests suffer from climate change-induced droughts. The hotter drought in Europe in 2018 with the consecutive drought years 2019 and 2020 caused large-scale growth declines and forest dieback. We investigated if tree growth responses to the 2018-2020 drought can be explained by tree functional traits related to drought tolerance, growth, and resource acquisition. C_LIO_LIWe assessed growth resistance, that is, growth during drought compared to pre-drought-conditions, in 71 planted tree species using branch shoot increments. We leveraged gap-filled trait data related to drought tolerance (P50, stomata density and conductivity), growth and resource acquisition (SLA, LNC, C:N, Amax) and wood density from the TRY database to explain growth resistance for gymnosperms and angiosperms. C_LIO_LIWe found significantly reduced growth during drought across all species. Legacy effects further decreased growth resistance in 2019 and 2020. Gymnosperms showed decreasing growth resistance with increasing P50 and acquisitiveness, such as high SLA, LNC, and Amax. Similar results were found for angiosperms, however, with less clear pattern. Four distinct response types emerged: Sufferer, Late sufferer, Recoverer and Resisters, with gymnosperms predominately falling into the Sufferer and Late sufferer categories. C_LIO_LIOur study provides evidence for significant growth reductions and legacy effects in response to consecutive hotter droughts, which can be explained by functional traits across a wide set of tree species. The a posteriori classification into response types revealed the diversity of temporal responses to a prolonged drought. We conclude that high drought tolerance bolsters growth resistance, while acquisitive species suffer stronger under drought. C_LI

ecology↗

bioRxiv2024

Tree growth is better explained by absorptive fine roots than transport fine roots

O_LIQuantifying plant trait variation yields insights into trade-offs inherent in the ecological strategies of plants and is the basis for a trait-based prediction of plant performance and ecosystem functioning. Although the interest in root traits has increased in recent years, we still have limited knowledge of i) whether functionally different fine roots--absorptive versus transport roots--have similar trait coordination and ii) how they help to explain plant performance, such as growth. C_LIO_LIWe measured traits of 25 European broadleaved tree species growing in a research arboretum to study i) the coordination of root traits within absorptive and transport fine roots and ii) the degree of trait-tree growth relationships. To do so, we combined a suite of morphological (root diameter, specific root length and root tissue density) and anatomical (cortex to stele ratio and arbuscular mycorrhizal colonization rate) traits for each of the absorptive and transport roots and also leaf traits (leaf mass per area, dry matter content and toughness). C_LIO_LIDespite remarkable differences in average trait values between absorptive and transport roots, our study shows that trait coordination within absorptive and transport roots is relatively equivalent. Our results also show that, for the traits we studied, tree growth is better explained by absorptive root traits than by transport root traits and is higher in species with a thinner root diameter. This suggests that variation primarily in absorptive roots affects the uptake of soil-based resources like nutrients and water and directly influences tree growth. C_LIO_LIThe significant relationship between absorptive roots and tree growth and the lack of such a relationship for transport roots highlights that roots mostly involved with resource absorption are more important in explaining tree growth than roots involved in transport. C_LI

ecology↗

bioRxiv2023

Post-ischemic ubiquitination at the postsynaptic density reversibly influences the activity of ischemia-relevant kinases

Ubiquitin modifications alter protein function and stability, thereby regulating cell homeostasis and viability, particularly under stress. Ischemic stroke induces protein ubiquitination at the ischemic periphery, wherein cells remain viable, however the identity of ubiquitinated proteins is unknown. Here, we employed a proteomics approach to identify these proteins in mice undergoing ischemic stroke. The data are available in a searchable web interface (https://hochrainerlab.shinyapps.io/StrokeUbiOmics/). We detected increased ubiquitination of 198 proteins, many of which localize to the postsynaptic density (PSD) of glutamatergic neurons. Among these were proteins essential for maintaining PSD architecture, such as PSD95, as well as NMDA and AMPA receptor subunits. The largest enzymatic group at the PSD with elevated post-ischemic ubiquitination were kinases, such as CaMKII, PKC, Cdk5, and Pyk2, whose aberrant activities are well-known to contribute to post-ischemic neuronal death. Concurrent phospho-proteomics revealed altered PSD-associated phosphorylation patterns, indicative of modified kinase activities following stroke. PSD-located CaMKII, PKC, and Cdk5 activities were decreased while Pyk2 activity was increased after stroke. Removal of ubiquitin restored kinase activities to pre-stroke levels, identifying ubiquitination as the responsible molecular mechanism for post-ischemic kinase regulation. These findings unveil a previously unrecognized role of ubiquitination in the regulation of essential kinases involved in ischemic injury.

neuroscience↗

bioRxiv2022

Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13C responses to drought

O_LIMixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. Particularly, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. C_LIO_LIUsing tree cores from a large-scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; {delta}13C) to changes in climate-induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases {delta}13C and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterized the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance vs resource acquisition and stomatal control. C_LIO_LITree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods. Neighbourhood species richness effects on growth and {delta}13C did not strengthen from wet to dry years. Instead, richness-growth and richness-{delta}13C relationships were modulated by climatic conditions and the traits of trees and their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during drought and non-drought years. C_LIO_LIWe show that species drought-tolerance traits can explain the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress. C_LI One-sentence summaryThe drought-tolerance traits of trees and their neighbours determine biodiversity-ecosystem functioning relationships in experimental tree communities.

ecology↗

bioRxiv2021

Cumulative growth and stress responses to the 2018-2019 drought in a European floodplain forest

Droughts increasingly threaten the worlds forests and their potential to mitigate climate change. In 2018-2019, Central European forests were hit by two consecutive hotter drought years, an unprecedented phenomenon that is likely to occur more frequently with climate change. Here, we examine tree growth and physiological stress responses (increase in carbon isotope composition; {Delta}{delta}13C) to this consecutive drought based on tree-rings of dominant tree species in a Central European floodplain forest. Tree growth was not reduced for most species in 2018, indicating that water supply in floodplain forests can partly buffer meteorological water deficits. Drought stress responses in 2018 were comparable to former single drought years but the hotter drought in 2018 induced drought legacies in tree growth while former droughts did not. We observed strong decreases in tree growth and increases in {Delta}{delta}13C across all tree species in 2019, which are likely driven by the cumulative stress both consecutive hotter droughts exerted. Our results show that consecutive hotter droughts pose a novel threat to forests under climate change, even in forest ecosystems with comparably high levels of water supply.

ecology↗