Steven Jansen

Ulm University | UULM · Institute of Botany

Summary: • Evolutionary radiations of woody taxa within arid environments were made possible by multiple trait innovations including deep roots and embolism-resistant xylem, but little is known about how these traits have coevolved across the phylogeny of woody plants or how they jointly influence the distribution of species. • We synthesized glob...

The increasing frequency of global change‐type droughts has created a need for fast, accurate and widely applicable techniques for estimating xylem embolism resistance to improve forecasts of future forest changes. We used data from 12 diffuse‐porous temperate tree species covering a wide range of xylem safety to compare the pneumatic and flow‐cent...

Intervessel pits are considered to function as valves that avoid embolism spreading and optimize efficient transport of xylem sap across neighbouring vessels. Hydraulic transport between vessels would therefore follow a safety-efficiency trade-off, which is directly related to the total intervessel pit area (A p), inversely related to the pit membr...

Water stored in trunk sapwood is vital for the canopy to maintain its physiological function under high transpiration demands. Little is known regarding the anatomical properties that contribute to the hydraulic capacitance of tree trunks, and whether trunk capacitance is correlated with the hydraulic and gas-exchange traits of canopy branches. We...

Considerable progress has been made in understanding the mechanisms of embolism formation based on the pneumatic method, which relies on gas discharge measurements. Here, we test the assumption that cut-open conduits are gas-filled when samples are cut at high water potentials. We performed vulnerability curves (VC) with the Pneumatron and analysed...

One of the more surprising occurrences of bulk nanobubbles is in the sap inside the vascular transport system of flowering plants, the xylem. In plants, nanobubbles are subjected to negative pressure in the water and to large pressure fluctuations, sometimes encompassing pressure changes of several MPa over the course of a single day, as well as wi...

Water stress can cause declines in plant function that persist after rehydration. Recent work has defined ‘resilience’ traits characterizing leaf resistance to persistent damage from drought, but whether these traits predict resilience in whole‐plant function is unknown. It is also unknown whether the coordination between resilience and ‘resistance...

Understanding xylem embolism formation is challenging due to dynamic changes and multiphase interactions in conduits. If embolism spread involves gas movement in xylem, we hypothesise that it is affected by time. We measured hydraulic conductivity (Kh) in flow-centrifuge experiments over one hour at a given pressure and temperature for stem samples...

This figure shows a transverse section of wood tissue from Hibiscus syriacus observed with a transmission electron microscope. One of the secrets behind water transport under negative pressure, which plants are able to do effortlessly on a daily basis, relies on our understanding of gas-water-solid interactions in porous cell walls between water co...

As Earth's climate has varied strongly through geological time, studying the impacts of past climate change on biodiversity helps to understand the risks from future climate change. However, it remains unclear how paleoclimate shapes spatial variation in biodiversity. Here, we assessed the influence of Quaternary climate change on spatial dissimila...

Lianas are increasing in relative abundance and biomass, mainly in seasonally dry forests, but it is unclear if this is associated with their hydraulic strategy. Here, we ask whether liana of seasonally dry forests are safer and more efficient in water transport than those of rainforest, which could explain liana distribution patterns and their rec...

Bordered pit membranes of angiosperm xylem are anisotropic, mesoporous media between neighbouring conduits, with a key role in long distance water transport. Yet, their mechanical properties are poorly understood. Here, we aim to quantify the stiffness of intervessel pit membranes over various growing seasons. By applying an AFM-based indentation t...

Although xylem embolism is a key process during drought‐induced tree mortality, its relationship to wood anatomy remains debated. While the functional link between bordered pits and embolism resistance is known, there is no direct, mechanistic explanation for the traditional assumption that wider vessels are more vulnerable than narrow ones. We use...

Here we provide the ‘Global Spectrum of Plant Form and Function Dataset’, containing species mean values for six vascular plant traits. Together, these traits –plant height, stem specific density, leaf area, leaf mass per area, leaf nitrogen content per dry mass, and diaspore (seed or spore) mass – define the primary axes of variation in plant form...

The Cretaceous–Cenozoic expansion of tropical forests created canopy space that was subsequently occupied by diverse epiphytic communities including Eupolypod ferns. Eupolypods proliferated in this more stressful niche, where lower competition enabled the adaptive radiation of thousands of species. Here, we examine whether xylem traits helped shape...

Fuel moisture content (FMC) is a crucial driver of forest fires in many regions world‐wide. Yet, the dynamics of FMC in forest canopies as well as their physiological and environmental determinants remain poorly understood, especially under extreme drought. We embedded a FMC module in the trait‐based, plant‐hydraulic SurEau‐Ecos model to provide in...

The resistance of xylem conduits to embolism is a major factor defining drought tolerance and can set the distributional limits of species across rainfall gradients. Recent work suggests that the proximity of vessels to neighbors increases the vulnerability of a conduit. We therefore investigated whether the relative vessel area of xylem correlates...

Background and Aims Ferns are the second largest group of vascular plants and are distributed nearly worldwide. Although ferns have been integrated into some comparative ecological studies focussing on hydathodes, there is a considerable gap in our understanding of the functional anatomy of these secretory tissues that are found on the vein endings...

The Pneumatic method has been introduced to quantify embolism resistance in plant xylem of various organs by applying a partial vacuum to cut-open xylem. Despite the similarity in vulnerability curves between the Pneumatic and other methods, a modeling approach is needed to investigate if changes in xylem embolism during dehydration can be accurate...

Hydraulic failure resulting from drought‐induced embolism in the xylem of plants is a key determinant of reduced productivity and mortality. Methods to assess this vulnerability are difficult to achieve at scale, leading to alternative metrics and correlations with more easily measured traits. Such efforts have led to the longstanding and pervasive...

Safeguarding Earth’s tree diversity is a conservation priority due to the importance of trees for biodiversity and ecosystem functions and services such as carbon sequestration. Here, we improve the foundation for effective conservation of global tree diversity by analyzing a recently developed database of tree species covering 46,752 species. We q...

Embolism spreading in xylem is an important component of plant drought resistance. Since embolism resistance has been shown to be mechanistically linked to pit membrane characters in stem xylem, we speculate that similar mechanisms account for leaf xylem. We conducted transmission electron microscopy to investigate pit membrane characters in leaf x...

In previous research, xylem sap of angiosperms has been found to include low concentrations of nanoparticles and polar lipids. A major goal of this study was to test predictions arising from the hypothesis that the nanoparticles consist largely of polar lipids from the original cell content of vessel elements. These predictions included that polar...

One of the most prominent changes in neotropical forests has been the increase in abundance and size of lianas. Studies suggest that lianas have more acquisitive strategies than trees, which could allow them to take advantage of water more effectively when it is available in water-limited forests, but few studies compared across growth form (i.e.,...

Extant conifer species are adapted to a range of climate conditions, which would be reflected in their xylem structure, especially in tracheid characteristics of early-and-latewood. With an anatomical dataset of 79 conifer species native to China, an interspecific study was conducted within a phylogenetic context to find latitudinal patterns in tra...

Simulations of the land surface carbon cycle typically compress functional diversity into a small set of plant functional types (PFT), with parameters defined by the average value of measurements of functional traits. In most earth system models, all wild plant life is represented by between five and 14 PFTs and a typical grid cell (≈100 × 100 km)...

Globally distributed extant conifer species must adapt to various environmental conditions, which would be reflected in their xylem structure, especially in the tracheid characteristics of earlywood and latewood. With an anatomical trait dataset of 78 conifer species growing throughout China, an interspecific study within a phylogenetic context was...

International online meeting on ‘Plant Pneumatics’, Ulm University and the University of Natural Resources and Life Sciences (BOKU), Ulm (Germany) and Vienna (Austria), 22 April and 29 September 2021

• Drought events may increase the likelihood that the plant water transport system becomes interrupted by embolism. Yet our knowledge about the temporal frequency of xylem embolism in the field is frequently lacking, as it requires detailed, long-term measurements. • We measured xylem embolism resistance and midday xylem water potentials during the...

Despite a long research history, we do not fully understand why plants are able to transport xylem sap under negative pressure without constant failure. Microbubble formation via direct gas entry is assumed to cause hydraulic failure, while the concentration of gas dissolved in xylem sap is traditionally supposed to be constant, following Henry's l...

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and...

Xylem embolism formation is a key process during drought-induced tree mortality, but its relationship to wood anatomical properties is debated. While the classical assumption is that larger vessels provoke a higher embolism risk, the evidence is mixed, and recent studies show that differences in embolism resistance are rather driven by pit membran...

The cover image is based on the Letter Hydraulic prediction of drought‐induced plant dieback and top-kill depends on leaf habit and growth form by Ya‐Jun Chen et al., https://doi.org/10.1111/ele.13856.

Xylem sap of angiosperm species has been found to include low concentrations of polar lipids and nanoparticles, including surfactant-coated nanobubbles. Although the nanoparticles have been suggested to consist of polar lipids, no attempt has been made to determine if nanoparticle and lipid concentrations are related. Here, we examined concentratio...

Premise: Among the sophisticated trap types in carnivorous plants, the underground eel-traps of corkskrew plants (Genlisea spp., Lentibulariaceae) are probably the least understood in terms of their functional principle. Here, we provide a detailed analysis of structural and hydraulic features of G. hispidula traps, contributing to the ongoing deb...

Premise: Extrafloral nectaries are mainly studied in angiosperms, but have also been reported in 39 fern species. Here we provide a global review of nectaries in ferns, and study their structure, function, and nectar sugar composition in two genera. Methods: We searched in the literature and living plant collections of botanical gardens for indi...

Hydraulic failure caused by severe drought contributes to aboveground dieback and whole-plant death. The extent to which dieback or whole-plant death can be predicted by plant hydraulic traits has rarely been tested among species with different leaf habits and/or growth forms. We investigated 19 hydraulic traits in 40 woody species in a tropical sa...

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and...

Background: Globally distributed extant conifer species must adapt to various environmental conditions, which would be reflected in their xylem structure, especially in the tracheid characteristics of earlywood and latewood. A comparative study of conifer species might shed light on how xylem structure responds to environmental conditions. With an...

Key message Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stem. However, although it has been intensively investigated these past decades, the extent to which vulnerability segmentation promotes drought resistance is not well understood. Based on a trait-based model, this study theoretically supports t...

Significance Invasive alien species pose major threats to biodiversity and ecosystems. However, identifying drivers of invasion success has been challenging, in part because species can achieve invasiveness in different ways, each corresponding to different aspects of demographics and distribution. Employing a multidimensional perspective of invasi...

The Pneumatron device measures gas diffusion kinetics in the xylem of plants. The device provides an easy, low-cost, and powerful tool for research on plant water relations and gas exchange. Here, we describe in detail how to construct and operate this device to estimate embolism resistance of angiosperm xylem, and how to analyse pneumatic data. Si...

Aim Here we examine the functional profile of regional tree species pools across the latitudinal distribution of Neotropical moist forests, and test trait–climate relationships among local communities. We expected opportunistic strategies (acquisitive traits, small seeds) to be overrepresented in species pools further from the equator, but also in...

The increasing frequency of global change-type droughts has created a need for fast, accurate and widely applicable techniques for estimating xylem embolism resistance to improve forecasts of future forest changes. We used data from 12 diffuse-porous temperate tree species covering a wide range of xylem safety to compare the pneumatic and flow-cent...

The Pneumatron device presented measures gas diffusion kinetics in the xylem of plants. The device provides an easy, low‐cost, and powerful tool for research on plant water relations. Here, we describe in detail how to construct and operate this device to estimate xylem vulnerability to embolism, and how to analyse pneumatic data. Simple and more e...

The Pneumatic method has been introduced to quantify embolism resistance in plant xylem of various organs. Despite striking similarity in vulnerability curves between the Pneumatic and hydraulic methods, a modeling approach is highly needed to demonstrate that xylem embolism resistance can be accurately quantified based on gas diffusion kinetics. A...

Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolised and sap‐filled conduits. Here, we examine how the proximity to pre‐existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compared xylem embolism resistance between detached leaves and leaves attached to...

Lipids have been observed attached to lumen-facing surfaces of mature xylem conduits of several plant species, but there has been little research on their functions or effects on water transport, and only one lipidomic study of the xylem apoplast. Therefore, we conducted lipidomic analyses of xylem sap from woody stems of seven plants representing...

Xylem resistance to drought‐induced embolism is an important trait determining plant distribution. In the karst hills of Southwest China, with a relatively small variation in altitude, soil depth and water availability strongly decrease from the foot towards the top, and woody plant species display distinct spatial distribution. For testing the hyp...

Purpose of Review Defining the mechanisms behind and the leaf economic consequences of the development of sclerophylly in woody plants will allow us to understand its ecological implications, anticipate the potential for adaptation of different tree species to global change, and define new woody plant ideotypes for stress tolerance. Recent Finding...

Background and Aims The acquisitive-conservative axis of plant ecological strategies results in a pattern of leaf trait covariation that captures the balance between leaf construction costs and plant growth potential. Studies evaluating trait covariation within species are scarcer, and have mostly dealt with variation in response to environmental g...

Although transpiration-driven transport of xylem sap is well known to operate under absolute negative pressure, many terrestrial, vascular plants show positive xylem pressure above atmospheric pressure on a seasonal or daily basis, or during early developmental stages. The actual location and mechanisms behind positive xylem pressure remain largely...

Both historical and contemporary environmental conditions determine present biodiversity patterns, but their relative importance is not well understood. One way to disentangle their relative effects is to assess how different dimensions of beta-diversity relate to past climatic changes, i.e., taxonomic, phylogenetic and functional compositional dis...

Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolised and sap-filled conduits. Here, we examine how proximity to pre-existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compared xylem embolism resistance between detached leaves and leaves attached to bran...

Biodiversity shortfalls are knowledge gaps that may result from uneven sampling through time and space and human interest biases. Gaps in data of functional traits of species may add uncertainty in functional diversity and structure measures and hinder inference on ecosystem functioning and ecosystem services, with negative implications for conserv...

Although xylem embolism resistance is traditionally considered as static, we hypothesized that in grapevine ( Vitis vinifera ) leaf xylem becomes more embolism‐resistant over the growing season. We evaluated xylem architecture, turgor loss point (Ψ TLP ) and water potentials leading to 25% of maximal stomatal conductance ( g s25 ) or 50% embolism i...

Knowledge about the length of xylem vessels is essential to understand water transport in plants because these multicellular units show a 100-fold variation, from less than a centimeter to many meters. However, the available methods to estimate vessel length (VL) distribution are excessively time consuming and do not allow large and in-depth survey...

Lipids have been observed attached to lumen-facing surfaces of mature xylem conduits of several plant species, but there has been little research on their functions or effects on water transport, and only one lipidomic study of the xylem apoplast. Therefore, we conducted lipidomic analyses of xylem sap from woody stems of seven plants representing...

Drought‐induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure–functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined o...

Comparisons among methods are essential to validate plant traits measured across studies. However, a rigorous analysis is a complex task that needs to take into account not only the principle of the method and its correct use, but also inherent intraspecific trait variability, something we feel is not fully considered by Sergent et al. (2020). They...

Climate change increases the occurrence of prolonged drought periods with large implications for forest functioning. Scots pine (Pinus sylvestris L.) is one of the most abundant conifers worldwide and evidence is rising that its resilience to severe drought is limited. However, we know little about its ability to recover from drought-induced emboli...