Many studies have reported that hydraulic properties vary considerably between tree species, but little is known about their intraspecific variation and, therefore, their capacity to adapt to a warmer and drier climate. Here, we quantify phenotypic divergence and clinal variation for embolism resistance, hydraulic conductivity and branch growth, in four tree species, two angiosperms (Betula pendula, Populus tremula) and two conifers (Picea abies, Pinus sylvestris), across their latitudinal distribution in Europe. Growth and hydraulic efficiency varied widely within species and between populations. The variability of embolism resistance was in general weaker than that of growth and hydraulic efficiency, and very low for all species but Populus tremula. In addition, no and weak support for a safety vs. efficiency trade-off was observed for the angiosperm and conifer species, respectively. The limited variability of embolism resistance observed here for all species except Populus tremula, suggests that forest populations will unlikely be able to adapt hydraulically to drier conditions through the evolution of embolism resistance.
- MeSH
- fenotyp MeSH
- lesy MeSH
- období sucha * MeSH
- podnebí MeSH
- stromy klasifikace fyziologie MeSH
- voda * MeSH
- xylém fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Evropa MeSH
Variation in xylem vessel diameter is one of the most important parameters when evaluating plant water relations. This review provides a synthesis of the ecophysiological implications of variation in lumen diameter together with a summary of our current understanding of vessel development and its endogenous regulation. We analyzed inter-specific variation of the mean hydraulic vessel diameter (Dv ) across biomes, intra-specific variation of Dv under natural and controlled conditions, and intra-plant variation. We found that the Dv measured in young branches tends to stay below 30 µm in regions experiencing winter frost, whereas it is highly variable in the tropical rainforest. Within a plant, the widest vessels are often found in the trunk and in large roots; smaller diameters have been reported for leaves and small lateral roots. Dv varies in response to environmental factors and is not only a function of plant size. Despite the wealth of data on vessel diameter variation, the regulation of diameter is poorly understood. Polar auxin transport through the vascular cambium is a key regulator linking foliar and xylem development. Limited evidence suggests that auxin transport is also a determinant of vessel diameter. The role of auxin in cell expansion and in establishing longitudinal continuity during secondary growth deserve further study.
Xylem vulnerability to embolism represents an essential trait for the evaluation of the impact of hydraulics in plant function and ecology. The standard centrifuge technique is widely used for the construction of vulnerability curves, although its accuracy when applied to species with long vessels remains under debate. We developed a simple diagnostic test to determine whether the open-vessel artefact influences centrifuge estimates of embolism resistance. Xylem samples from three species with differing vessel lengths were exposed to less negative xylem pressures via centrifugation than the minimum pressure the sample had previously experienced. Additional calibration was obtained from non-invasive measurement of embolism on intact olive plants by X-ray microtomography. Results showed artefactual decreases in hydraulic conductance (k) for samples with open vessels when exposed to a less negative xylem pressure than the minimum pressure they had previously experienced. X-Ray microtomography indicated that most of the embolism formation in olive occurs at xylem pressures below -4.0 MPa, reaching 50% loss of hydraulic conductivity at -5.3 MPa. The artefactual reductions in k induced by centrifugation underestimate embolism resistance data of species with long vessels. A simple test is suggested to avoid this open vessel artefact and to ensure the reliability of this technique in future studies.
- MeSH
- nemoci rostlin * MeSH
- Olea fyziologie MeSH
- voda metabolismus MeSH
- xylém metabolismus fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
Vessels with simple perforation plates, found in the majority of angiosperms, are considered the evolutionarily most advanced conduits, least impeding the xylem sap flow. Nevertheless, when measured, their hydraulic resistivity (R, i.e., inverse value of hydraulic conductivity) is significantly higher than resistivity predicted using Hagen-Poiseuille equation (RHP). In our study we aimed (i) to quantify two basic components of the total vessel resistivity - vessel lumen resistivity and end wall resistivity, and (ii) to analyze how the variable inner diameter of the vessel along its longitudinal axis affects resistivity. We measured flow rates through progressively shortened stems of hop (Humulus lupulus L.), grapevine (Vitis vinifera L.), and clematis (Clematis vitalba L.) and used elastomer injection for identification of open vessels and for measurement of changing vessel inner diameters along its axis. The relative contribution of end wall resistivity to total vessel resistivity was 0.46 for hop, 0.55 for grapevine, and 0.30 for clematis. Vessel lumen resistivity calculated from our measurements was substantially higher than theoretical resistivity - about 43% for hop, 58% for grapevine, and 52% for clematis. We identified variation in the vessel inner diameter as an important source of vessel resistivity. The coefficient of variation of vessel inner diameter was a good predictor for the increase of the ratio of integral RHP to RHP calculated from the mean value of inner vessel diameter. We discuss the fact that we dealt with the longest vessels in a given stem sample, which may lead to the overestimation of vessel lumen resistivity, which consequently precludes decision whether the variable vessel inner diameter explains fully the difference between vessel lumen resistivity and RHP we observed.
The Rhinanthoid clade of the family Orobanchaceae comprises plants displaying a hemiparasitic or holoparasitic strategy of resource acquisition. Some of its species (mainly Rhinanthus spp.) are often used as models for studies of hemiparasite physiology. Although there is a well-developed concept covering their physiological processes, most recent studies have neglected the existence of hydathode trichomes present on leaves of these hemiparasitic plants. As a first step for the proposed integration of these structures in the theory of physiological processes of the hemiparasites, we described the outer micromorphology and ultrastructure of the hydathode trichomes on leaves of hemiparasitic Rhinanthus alectorolophus and Odontites vernus with scanning and transmission electron microscopy (SEM and TEM, respectively). The TEM inspections of both types of trichome revealed typical ultrastructural features: labyrinthine cell wall, high content of cytoplasm in cells with numerous mitochondria and presence of plasmodesmata. All these features indicate high metabolic activity complying with their function as glandular trichomes actively secreting water. The active secretion of water by the hydathode trichomes (evidence for which is summarised here) also presents a possible mechanism explaining results of previous gas exchange measurements detecting high dark respiration and transpiration rates and a tight inter-correlation between them in hemiparasitic Orobanchaceae. In addition, this process is hypothesised to have allowed multiple evolutionary transitions from facultative to obligate hemiparasitism and unique xylem-feeding holoparasitism of Lathraea with a long-lived underground stage featuring a rhizome covered by scales of leaf origin.
- MeSH
- biologická evoluce MeSH
- buněčná stěna ultrastruktura MeSH
- buněčné dýchání MeSH
- epidermis rostlin genetika fyziologie ultrastruktura MeSH
- listy rostlin genetika fyziologie ultrastruktura MeSH
- mikroskopie elektronová rastrovací MeSH
- mitochondrie ultrastruktura MeSH
- Orobanchaceae genetika fyziologie ultrastruktura MeSH
- plazmodesmy ultrastruktura MeSH
- transmisní elektronová mikroskopie MeSH
- transpirace rostlin MeSH
- voda metabolismus MeSH
- xylém genetika fyziologie ultrastruktura MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Several electrical methods have been introduced as non-invasive techniques to overcome the limited accessibility to root systems. Among them, the earth impedance method (EIM) represents the most recent development. Applying an electrical field between a cormus and the rooted soil, the EIM measures the absorptive root surface area (ARSA) from grounding resistance patterns. Allometric relationships suggested that this method was a valuable tool. Crucial assumptions for the applicability of the EIM, however, have not been tested experimentally. Focusing on tree root systems, the present study assesses the applicability of the EIM. Six hypotheses, deduced from the EIM approach, were tested in several experiments and the results were compared with conventional methods. None of the hypotheses could be verified and the results allow two major conclusions. First, in terms of an analogue electrical circuit, a tree-root-soil continuum appears as a serial circuit with xylem and soil resistance being the dominant components. Allometric variation in contact resistance, with the latter being the proxy for root surface area, are thus overruled by the spatial and seasonal variation of soil and xylem resistances. Second, in a tree-root-soil continuum, distal roots conduct only a negligible portion of the electric charge. Most of charge carriers leave the root system in the proximal parts of the root-soil interface.
- MeSH
- algoritmy MeSH
- biometrie MeSH
- cykasy MeSH
- elektrická impedance MeSH
- kořeny rostlin anatomie a histologie fyziologie MeSH
- Magnoliopsida MeSH
- průmyslová hnojiva MeSH
- půda MeSH
- roční období MeSH
- stromy anatomie a histologie fyziologie MeSH
- xylém fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
