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January 1998 - present
February 2015 - present
Publications
Publications (72)
The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions...
The Arctic forests of the Eocene, which thrived under elevated CO2, a temperate climate, high precipitation and annually extremely different daylengths, represent a quite spectacular no‐analogue habitat of Earth's greenhouse past. The aim of this study was to improve our understanding of the ecophysiology of Arctic broad‐leaved deciduous forests of...
Xylem vulnerability to embolism can be quantified by “vulnerability curves” (VC) that are obtained by subjecting wood samples to increasingly negative water potential and monitoring the progressive loss of hydraulic conductivity. VC are typically sigmoidal, and various approaches are used to fit the experimentally obtained VC data for extracting be...
The history of the long‐distance transport systems of vascular plants, phloem, and xylem, is a long and winding road of scientific progress which fascinated and occupied foresters, botanists, and physicists during the last 250 years. Although the Münch pressure flow hypothesis of phloem transport is meanwhile generally accepted, some details are no...
Cuticles are extracellular membranes covering the primary aerial parts of vascular plants. They consist of a multifunctional polymeric material with embedded soluble components called waxes, and serve as the interface between plants and their atmospheric environment, first of all protecting them from desiccation. Remarkably, damaged wax layers may...
The potential of spider silk as an intriguing biological prototype for collecting water from a humid environment has attracted wide attention, and various materials with suitable structures have been engineered. Here, inspired by this phenomenon, a kind of superwetting poly(vinylidene fluoride) (PVDF) membrane with spindle-knotted structured fibers...
There are currently efforts to improve strategies for biomimetic approaches, to identify pitfalls and to provide recommendations for a successful biomimetic work flow. In this contribution, a case study of a concrete biomimetic project is described that started with a posed technical problem for which seemingly obvious biological models exist. The...
The contamination of water with oil from industrial processes has become a worldwide problem that requires the development of efficient, reliable and economical separation methods. Inspired by droplet movements on spider silk, we present in this contribution a model of the separation of oil and water that is based on the effect that liquid droplets...
Raindrop impact on leaves is a common event which is of relevance for numerous processes, including the dispersal
of pathogens and propagules, leaf wax erosion, gas exchange, leaf water absorption, and interception and storage
of rainwater by canopies. The process of drop impact is complex, and its outcome depends on many influential factors.
The w...
The contamination of water with oil from industrial processes has become a worldwide problem that requires the development of efficient, reliable and economical separation methods. Inspired by droplet movements on spider silk, we present in this contribution a model of the separation of oil and water that is based on the effect that liquid droplets...
The floating leaves of the aquatic fern Salvinia molesta are covered by super-hydrophobic hairs (=trichomes) which are shaped like egg-beaters. These trichomes cause high water repellency and stable unwettability if the leaf is immersed. Whereas S. molesta hairs are technically interesting, there remains also the question concerning their biologica...
The determination of the dynamic contact angle is of significant interest for the characterization of the wettability of technical fibers and textiles in diverse fields of science and technology. There exist traditional methods for dynamic contact angle measurements of flat surfaces and of fibers with a uniform cross‐sectional shape along the fiber...
Trees are the fundamental element of forest ecosystems, made possible by their mechanical qualities and their highly sophisticated conductive tissues. The evolution of trees, and thereby the evolution of forests, were ecologically transformative and affected climate and biogeochemical cycles fundamentally. Trees also offer a substantial amount of e...
Aerial roots of orchids are able to absorb atmospheric water (e.g. rain, mist, dew) and to conduct it to the root interior. The water is absorbed by imbibition into a biological porous material, the velamen radicum, which envelops the aerial root and comprises one or two to several layers. The velamen radicum consists of walls of dead cells and sho...
A variety of proxies have been developed to reconstruct paleo‐CO2 from fossil leaves. These proxies rely on some combination of stomatal morphology, leaf δ13C, and leaf gas exchange. A common conceptual framework for evaluating these proxies is lacking, which has hampered efforts for inter‐comparison. Here we develop such a framework, based on the...
There is general concern that the rapid increase in atmospheric CO2 concentration will lead to reduced stomatal conductance and subsequent increases in leaf temperature. Such an increase in leaf temperature is expected to adversely impact a plethora of processes connected to leaf metabolism and microbial/fungal communities on leaves. A model is pro...
Leaves are the most appropriate plant organs for studying adaptations to environmental changes as they are the locations of photosynthetic metabolism and thus directly exposed to habitat conditions. Besides investigations on complete assemblages, individual long-ranging species could directly mirror adaptations and changes of leaf traits on environ...
In frost hardy plants, the lethal intracellular formation of ice crystals has to be prevented during frost periods. Besides the ability for supercooling and pre-frost dehydration of tissues, extracellular ice forma- tion is another strategy to control ice development in tissues. During extracellular ice formation, partially large ice bodies accumul...
Functional properties of biological surfaces have gained increasing interest in the last two decades, especially with regard to wetting and self-cleaning. Here, biological surfaces of arthropods (Collembola) and plants (sacred Lotus) served as models for the principle design of high temperature resistant surfaces used in blast furnaces to prevent t...
Proxy estimates of atmospheric CO2 are necessary to reconstruct Earth's climate history. Confidence in paleo-CO2 estimates can be increased by comparing results from multiple proxies at a single site, but so far this strategy has been implemented only for marine-based techniques. Here we present CO2 estimates for the well-studied early Paleocene Ca...
Xylem and phloem are the two main conveyance systems in plants allowing exchanges of water and carbohydrates between roots and leaves. While each system has been studied in isolation for well over a century, the coupling and coordination between them remains the subject of inquiry and active research and frames the scope of the review here. Using a...
During land plant evolution many groups developed the ability to survive freezing events. Extracellular freezing is an essential
process, it accompanies cell dehydration mechanism and protects the living tissue from internal damage which would be evoked
by intracellular ice crystal growth. Within our project we studied freezing of various frost har...
Correlations of leaf traits with environmental conditions are widely used for reconstruction of palaeoclimate and to analyse the evolution of land plants. Evaluation of climate-dependent leaf traits of fossil floras can potentially contribute to our understanding of long-term responses of vegetation to changing climate. In this contribution, basic...
Cuticles are extracellular membranes covering the primary aerial parts of vascular plants. They consist of a multifunctional polymeric material with embedded soluble components called waxes, and serve as the interface between plants and their atmospheric environment, first of all protecting them from desiccation. Remarkably, damaged wax layers may...
To address questions related to the acceleration or deceleration of the global hydrological cycle or links between the carbon and water cycles over land, reliable data for past climatic conditions based on proxies are required. In particular, the reconstruction of palaeoatmospheric CO2 content (Ca) is needed to assist the separation of natural from...
Aerial roots of epiphytic orchids cannot absorb water from the soil but supply the plant by collecting atmospheric water together with dissolved nutrients. A special outer tissue layer, the velamen radicum (VR), consisting of dead cells, is crucial for water interception and absorption. In this contribution, the VR is explored as an intricate porou...
Recently, several leaf fossils with good cuticles were discovered from the Oligocene deposits in Guangxi, China. The high fossilization potential of these leaves and easily identifiable stomata and epidermal cells make them an excellent source for CO2 reconstruction. In this study, atmospheric CO2 of the Oligocene is reconstructed using the mechani...
Cuticles are extracellular membranes covering the primary aerial parts of vascular plants. They consist of a multifunctional polymeric material with embedded soluble components, called waxes and serve as the interface between plants and their atmospheric environment, first of all protecting them from desiccation. Waxes are produced within the epide...
Glandular trichomes of the carnivorous plant Roridula gorgonias release a viscous resinous secretion. Its adhesion to hydrophilic and hydrophobic glass surfaces was measured in air and underwater. The underwater adhesion reached up to 91% (on hydrophilic glass) and 28% (on hydrophobic glass) of that measured in the air. After being submersed for 24...
There is various evidence that the presence of condensed water, e.g. dew, improves plant water relations. Since particularly plants in drier environments are expected to benefit from atmospheric water, it may be assumed that special adaptations promoting exploitation of dew water evolved in these habitats. Surface characteristics affect dewfall and...
The late Oligocene represents a comparatively cool phase followed by a warming event, the so-called Late Oligocene Warming that predates the Mi-1 glacial event at the Oligocene–Miocene transition. There is evidence that these climate events were linked to level changes in atmospheric CO2. In this study, atmospheric CO2 from the late Oligocene to th...
In the Cenozoic era, global climate changed from greenhouse to icehouse
conditions. During the Oligocene, the comparatively cool phase in the
earlier part of the late Oligocene is followed by the Late Oligocene
Warming and a major glaciation event at the Oligocene-Miocene transition
(Mi-1). Various studies indicate that these climate events were co...
Background and AimsCold neutron radiography was applied to directly observe embolism in conduits of liana stems with the aim to evaluate the suitability of this method for studying embolism formation and repair. Potential advantages of this method are a principally non-invasive imaging approach with low energy dose compared with synchrotron X-ray r...
It has repeatedly been reported that stomatal pore length changes with changing atmospheric CO2 concentration. Since stomatal pore length affects stomatal conductance, the question arises of how pore length change interacts with the application of stomatal density as a CO2 proxy. In this study, stomatal density, pore length and maximum stomatal con...
The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are ana...
During photosynthesis, plants inevitably lose water that has to be continuously replaced by soil water absorbed by the roots. Hydrological status of the soil, root absorption, plant water transport, gas exchange and atmosphere are therefore intricately coupled within the soil-plant-atmosphere continuum (SPAC). It appears therefore straighforward to...
In this study, atmospheric CO2 during the early middle Eocene (~ 47Ma) is reconstructed using fossil plants from the Messel Formation close to Darmstadt, Germany. CO2 concentration is calculated using a mechanistic model of gas exchange which optimizes CO2 uptake by photosynthesis against water vapor loss by transpiration, a strategy that is common...
Wettability and retention capacity of leaf surfaces are parameters that contribute to interception of rain, fog or dew by forest canopies. Contrary to common expectation, hydrophobicity or wettability of a leaf do not dictate the stickiness of drops to leaves. Crucial for the adhesion of drops is the contact angle hysteresis, the difference between...
Background:
Controlled transport of microdroplets is a topic of interest for various applications. It is well known that liquid droplets move towards areas of minimum contact angle if placed on a flat solid surface exhibiting a gradient of contact angle. This effect can be utilised for droplet manipulation. In this contribution we describe how con...
For various plants and animals, the accumulation of fog or dew droplets constitutes an essential part of their water supply. Understanding how water droplets deposited by fog or dew events interact with plant or animal surfaces is essential for gaining insight into the functionality of these surfaces. Besides being interesting within the realm of b...
The Oligocene-Miocene transition represents a period in earth history marked by rapid cooling and glaciation of Antarctica, accompanied by a positive shift in delta13C and delta18O. According to modelling studies, formation of substantial Antarctic ice sheets requires pCO2atm to decrease below 500 ppm. Various proxies (such as Boron isotopes and de...
Various proxies (such as pedogenic carbonates, boron isotopes or phytoplankton) and geochemical models were applied in order to reconstruct palaeoatmospheric carbon dioxide, partially providing conflicting results. Another promising proxy is the frequency of stomata (pores on the leaf surface used for gaseous exchange). In this project, fossil plan...
We present a systematic derivation of the relation between stomatal
density and CO2concentration based upon (i) a quantitative model of
C3-photosynthesis, (ii) the physics of diffusion, and (iii) an
optimisation principle which asserts that plants adjust stomatal
conductance such that assimilation is maximised and transpiration is
minimised. Since...
We describe a few mathematical tools which allow to investigate whether air-water interfaces exist (under prescribed conditions) and are mechanically stable and temporally persistent. In terms of physics, air-water interfaces are governed by the Young-Laplace equation. Mathematically they are surfaces of constant mean curvature which represent solu...
Gas-filling of conduits decreases hydraulic conductance of the xylem vessels. Therefo re, embolism formation and reversal is one of the crucial topics in plant water transport. The negative pressure (=tension) in xylem water during plant transpiration may cause embolism in tw o ways: (i) Homogeneous nucleation, the spontaneous formation of a water...
It is assumed that changes in atmospheric CO2 concentrations (from now on expressed as Ca) strongly influenced the development of global temperatures during parts of the Cenozoic. Thus, detailed knowledge of ancient Ca and its variations is of utmost importance for exploring the coupling of atmospheric CO2 and global climate change. Numerous techni...
In this study, contaminant leaching from three different secondary materials (demolition waste, municipal solid waste incineration ash, and blast furnace slag) to groundwater is assessed by numerical modeling. Reactive transport simulations for a noise protection dam and a road dam (a typical German autobahn), in which secondary materials are reuse...
Stomatal density tends to vary inversely with changes in atmospheric CO(2) concentration (C(a)). This phenomenon is of significance due to: (i) the current anthropogenic rise in C(a) and its impact on vegetation, and (ii) the potential applicability for reconstructing palaeoatmospheric C(a) by using fossil plant remains. It is generally assumed tha...
In this study, groundwater contamination from recycled demolition waste in road constructions is assessed using predictions of leachate concentrations. Numerical transport simulations are performed for three scenarios ( a parking lot, a noise protection barrier, and road), and using a number of characteristic subsoils of Germany, to estimate the br...
The often observed reciprocal change of stomatal density (SD) or stomatal index (SI) with atmospheric CO2 has led to the utilization of this phenomenon as a CO2 proxy for past paleoclimates. Usually, data of the SD or SI(CO2) relationship of extant plants are used for empirical calibration in order to calculate past CO2 with fossil stomatal data. I...
A mechanistic model (Konrad &Roth-Nebelsick a, in prep.) was applied for the reconstruction of atmospheric carbon dioxide using stomatal densities and photosynthesis parameters of extant and fossil Fagaceae. The model is based on an approach which couples diffusion and the biochemical process of photosynthesis. Atmospheric CO2 is calculated on the...
During plant water transport, the water in the conducting tissue (xylem) is under tension. The system is then in a metastable state and prone to bubble development and subsequent embolism blocking further water transport. It has recently been demonstrated, that embolism can be repaired under tension (= novel refilling). A model (Pit Valve Mechanism...
Gaseous exchange in land plants occurs via micropores on the plant surface, the stomata. The stomatal frequency (SF) of leaves has attracted considerable interest with respect to increasing atmospheric CO2 since Woodward (1987) demonstrated that this parameter changes inversely with CO2 in various species. The response is due to 1) individual pheno...
The characteristic basic construction of early land plants with an upright posture is represented by a simple leaf- and rootless axis system with a central conducting bundle (‘rhyniophytic habit’). Variations of this simple architectural principle in different early land plant taxa probably reflect different ecophysiological requirements. In this c...
Pressure-induced tensions in the xylem, the water conducting tissue of vascular plants, can lead to embolism in the water-conducting cells. The details and mechanisms of embolism repair in vascular plants are still not well understood. In particular, experimental results which indicate that embolism repair may occur during xylem tension cause great...
Early terrestrial ancestors of the land flora are characterized by a simple, axially symmetric habit and evolved in an atmosphere with much higher CO(2)concentrations than today. In order to gain information about the ecophysiological interrelationships of these plants, a model dealing with their gaseous exchange, which is basic to transpiration an...
83C05 Einstein's equations (general structure, canonical formalism, Cauchy problems)
83C15 Exact solutions
83C57 Black holes
A model system, consisting of a thin spherical shell with radiusR and massM and a point massm at a distances>R from the center of the sphere, held fixed by an appropriate strut, is solved to ordermM. The stresses in the shell are not of the canonical Weyl type, and it is argued that the same is true for more realistic situations, e.g., rotating mat...
