Field experiment on water transport of oak trees measured by computer tomograph and magnetic resonance imaging (original) (raw)
Related papers
Axial and radial water flow in the trunks of oak trees: a quantitative and qualitative analysis
Tree Physiology, 1994
Axial water flow in the trunks of mature oak trees (Quercus petraea (Matt.) Liebl. and Q. robur L.) was studied by four independent techniques: water absorption from a cut trunk, sap flowmeters, heat pulse velocity (HPV) and thermoimaging. Estimation of the total water flow with sap flowmeters, HPV and water absorption yielded comparable results. We concluded from dye colorations, thermograms and axial profiles of sap flow and heat pulse velocity that, in intact trunks, most of the flow occurred in the current-year ring, where early-wood vessels in the outermost ring were still functional. Nevertheless, there was significant flow in the older rings of the xylem. Total water flow through the trunk was only slightly reduced when air embolisms were artificially induced in early-wood vessels, probably because there was little change in hydraulic conductance in the root-leaf sap pathway. Embolization of the current-year vessels reactivated transport in the older rings.
Trees, 2008
To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F d ) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water transportation such as spatial variations in F d and the active xylem area in the stem crosssection. Although evergreen oak trees with radial-porous wood represent a major component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and radial variations in the F d of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the xylem structure, we examined why F d varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk, we confirmed that the entire stem is hydroactive. We also compared the spatial variations in F d and water conductivity per xylem area (K s ) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen-Poiseuille's law. Azimuthal and radial variations in F d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K s . As a result, we obtained statistical parameters describing the spatial variation in F d in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for studied trees.
Radial variations in xylem sap flow and their effect on whole-tree water use estimates
Hydrological Processes, 2015
To estimate whole-tree or stand transpiration based on sap flow measurements, sap flux density (F d) needs to be scaled up over the entire sapwood area. We investigated radial variations in F d in the dominant oak (Quercus liaotungensis) and a commonly occurring oriental arborvitae (Platycladus orientalis) species using Granier-type thermal dissipation probes in a semi-arid forest in northern China. Our results show that F d in oak trees reached a maximum just below the cambium and decreased towards the inner sapwood. On the other hand, radial sap flow patterns in oriental arborvitae trees differed among individuals. F d values at different depths within an individual were highly correlated with each other in both species. We assessed the error of single-depth measurements when upscaling to whole-tree water use using multi-depth measurements as a reference. Omitting radial variations resulted in an overestimation of daily water use by 38% and 78% in oak trees with sapwood depths of approximately 2 and 3 cm, respectively. The outer sapwood annuli (0-1 cm) contributed 74% and 65% to the total water use in the two classes of sapwood depth. These contribution coefficients may be used as correction indices for estimating whole-tree water use. Errors of omitting radial variations in oriental arborvitae trees ranged from À42% to 21%. Using relatively long sensors (e.g. 2 cm) may improve the estimate accuracy in this species. The results would be applicable to the estimation of tree or stand transpiration based on routine depth measurements using one set of sensors. It is suggested that radial variations should be considered for accurately upscaling locally measured sap flow data to whole-tree water use in trees with wide sapwood and that different approaches may be applied to species with different patterns of radial variations.
PLANT PHYSIOLOGY, 2007
Due to the fragile pressure gradients present in the xylem and phloem, methods to study sap flow must be minimally invasive. Magnetic resonance imaging (MRI) meets this condition. A dedicated MRI method to study sap flow has been applied to quantify long-distance xylem flow and hydraulics in an intact cucumber (Cucumis sativus) plant. The accuracy of this MRI method to quantify sap flow and effective flow-conducting area is demonstrated by measuring the flow characteristics of the water in a virtual slice through the stem and comparing the results with water uptake data and microscopy. The in-plane image resolution of 120 3 120 mm was high enough to distinguish large individual xylem vessels. Cooling the roots of the plant severely inhibited water uptake by the roots and increased the hydraulic resistance of the plant stem. This increase is at least partially due to the formation of embolisms in the xylem vessels. Refilling the larger vessels seems to be a lengthy process. Refilling started in the night after root cooling and continued while neighboring vessels at a distance of not more than 0.4 mm transported an equal amount of water as before root cooling. Relative differences in volume flow in different vascular bundles suggest differences in xylem tension for different vascular bundles. The amount of data and detail that are presented for this single plant demonstrates new possibilities for using MRI in studying the dynamics of long-distance transport in plants.
Acta Horticulturae, 2018
Sap flow sensors and other techniques are commonly used across species and plant organs to quantify water use and storage, detect stress, and evaluate the contribution of various tissues to plant/organ water balance. Sap flow methods often rely upon modelling or assumptions about how heat delivered by the sap flow sensors is partitioned into convection and conduction into active sapwood xylem and surrounding tissues. Dynamic changes in tissue water content over space and time can impact the interpretation of plant and organ water use and how various compartments contribute to an integrated response to plant stress. Here, we first summarize results from a variety of studies that used a combination of synchrotron-based X-ray microCT and MRI imaging to demonstrate how water content of various organs and xylem cell types can change temporally and how the spatial distribution of air-filled tissue may impact patterns of sap flow within the xylem network. Results from visualization techniques were compared to that from traditional hydraulic and sap flow methods to illustrate potential discrepancies particularly when comparing data from excised stems versus intact plants. Using a spatially explicit model, we demonstrate how changes in the water content of various cell types can impact resulting interpretation of sensor output. Implications for the interpretation of sap flow and other sensor data based on these results is discussed.
Water transport in trees: current perspectives, new insights and some controversies
Environmental and Experimental Botany, 2001
This review emphasizes recent developments and controversies related to the uptake, transport and loss of water by trees. Comparisons of the stable isotope composition of soil and xylem water have provided new and sometimes unexpected insights concerning spatial and temporal partitioning of soil water by roots. Passive, hydraulic redistribution of water from moister to drier portions of the soil profile via plant root systems may have a substantial impact on vertical profiles of soil water distribution, partitioning of water within and among species, and on ecosystem water balance. The recent development of a technique for direct measurement of pressure in individual xylem elements of intact, transpiring plants elicited a number of challenges to the century-old cohesion-tension theory. The ongoing debate over mechanisms of long-distance water transport has stimulated an intense interest in the phenomenon and mechanisms of embolism repair. Rather than embolism being essentially irreversible, it now appears that there is a dynamic balance between embolism formation and repair throughout the day and that daily release of water from the xylem via cavitation may serve to stabilize leaf water balance by minimizing the temporal imbalance between water supply and demand. Leaf physiology is closely linked to hydraulic architecture and hydraulic perturbations, but the precise nature of the signals to which stomata respond remains to be elucidated. When water transport in trees is studied at multiple scales from single leaves to the whole organism, considerable functional convergence in regulation of water use among phylogenetically diverse species is revealed.
MRI links stem water content to stem diameter variations in transpiring trees
Journal of Experimental Botany, 2012
In trees, stem diameter variations are related to changes in stem water content, because internally stored water is depleted and replenished over a day. To confirm this relationship, non-invasive magnetic resonance imaging (MRI) was combined with point dendrometer measurements in three actively transpiring oak (Quercus robur L.) trees. Two of these oak trees were girdled to study the stem increment above the girdling zone. MRI images and micrographs of stem cross-sections revealed a close link between the water distribution and the anatomical features of the stem. Stem tissues with the highest amount of water were physiologically the most active ones, being the youngest differentiating xylem cells, the cambium and the youngest differentiating and conductive phloem cells. Daily changes in stem diameter corresponded well with the simultaneously MRI-measured amount of water, confirming their strong interdependence. MRI images also revealed that the amount of water in the elastic bark tissues, excluding cambium and the youngest phloem, contributed most to the daily stem diameter changes. After bark removal, an additional increase in stem diameter was measured above the girdle. This increase was attributed not only to the cambial production of new cells, but also to swelling of existing bark cells. In conclusion, the comparison of MRI and dendrometer measurements confirmed previous interpretations and applications of dendrometers and illustrates the additional and complementary information MRI can reveal regarding water relations in plants.
Chemosphere, 1998
Sap-flow of Quercus robur, Quercus petraea and Quercus cerris oak trees were studied.°'K radioisotope tracing, the heat pulse velocity technique and the Granier-method were employed. Numerous intense pulses were observed in healthy Quercus petraea superposing onto the usual diurnal change. Only a few pulses were observed in unhealthy Quercus petraea, in healthy Quercus cerris and healthy and unhealthy Quercus robur trees. Proportion of wet-wood assessed by y-and X-ray computer tomography and magnetic resonance imaging was significantly less in healthy Quercus petraea trees than in healthy Quercus cerris trees. Proportion of wet-wood was higher in healthy trees than unhealthy trees of both species .
Plant, Cell and Environment, 2006
We used dedicated magnetic resonance imaging (MRI) equipment and methods to study phloem and xylem transport in large potted plants. Quantitative flow profiles were obtained on a per-pixel basis, giving parameter maps of velocity, flow-conducting area and volume flow (flux). The diurnal xylem and phloem flow dynamics in poplar, castor bean, tomato and tobacco were compared. In poplar, clear diurnal differences in phloem flow profile were found, but phloem flux remained constant. In tomato, only small diurnal differences in flow profile were observed. In castor bean and tobacco, phloem flow remained unchanged. In all plants, xylem flow profiles showed large diurnal variation. Decreases in xylem flux were accompanied by a decrease in velocity and flow-conducting area. The diurnal changes in flow-conducting area of phloem and xylem could not be explained by pressure-dependent elastic changes in conduit diameter. The phloem to xylem flux ratio reflects what fraction of xylem water is used for phloem transport (Münch's counterflow). This ratio was large at night for poplar (0.19), castor bean (0.37) and tobacco (0.55), but low in tomato (0.04). The differences in phloem flow velocity between the four species, as well as within a diurnal cycle, were remarkably small (0.25-0.40 mm s -1 ). We hypothesize that upper and lower bounds for phloem flow velocity may exist: when phloem flow velocity is too high, parietal organelles may be stripped away from sieve tube walls; when sap flow is too slow or is highly variable, phloem-borne signalling could become unpredictable.
International Journal of Heat and Mass Transfer, 2012
Liquid water uptake in an orthotropic, cellular, hierarchical and natural material namely wood is investigated using neutron radiography. During water uptake in wood, liquid does not move up as a regular front as uptake rates differ in latewood and earlywood. In addition, moisture is adsorbed by the cell wall, resulting in a swelling that influences the process of moisture transport in wood. The high sensitivity of neutron to hydrogen atoms enables an accurate determination of the change in moisture content in the wood at the growth ring scale. The analysis of the spatial and temporal change of water content distribution shows that liquid water transport has different characteristics, depending on the direction of uptake and initial moisture content state.