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Kathy Steppe - One of the best experts on this subject based on the ideXlab platform.
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isotope ratio laser spectroscopy to disentangle xylem transported from locally respired co2 in stem co2 efflux
Tree Physiology, 2019Co-Authors: Roberto L Salomon, Linus De Roo, Samuel Bode, Pascal Boeckx, Kathy SteppeAbstract:Respired CO2 in woody tissues radially diffuses to the atmosphere or it is transported upward with the Transpiration Stream, making the origin of CO2 in stem CO2 efflux (EA) uncertain, which may confound stem respiration (RS) estimates. An aqueous 13C-enriched solution was infused into stems of Populus tremula L. trees, and real-time measurements of 13C-CO2 and 12C-CO2 in EA were performed via Cavity Ring Down Laser Spectroscopy (CRDS). The contribution of locally respired CO2 (LCO2) and xylem-transported CO2 (TCO2) to EA was estimated from their different isotopic composition. Mean daily values of TCO2/EA ranged from 13% to 38%, evidencing the notable role that xylem CO2 transport plays in the assessment of stem respiration. Mean daily TCO2/EA did not differ between treatments of drought stress and light exclusion of woody tissues, but they showed different TCO2/EA dynamics on a sub-daily time scale. Sub-daily CO2 diffusion patterns were explained by a light-induced axial CO2 gradient ascribed to woody tissue photosynthesis, and the resistance to radial CO2 diffusion determined by bark water content. Here, we demonstrate the outstanding potential of CRDS paired with 13C-CO2 labelling to advance in the understanding of CO2 movement at the plant-atmosphere interface and the respiratory physiology in woody tissues.
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stem girdling affects the quantity of co2 transported in xylem as well as co2 efflux from soil
New Phytologist, 2014Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Laura Agneessens, Lieven Van Meulebroek, Kathy SteppeAbstract:Summary There is recent clear evidence that an important fraction of root-respired CO2 is transported upward in the Transpiration Stream in tree stems rather than fluxing to the soil. In this study, we aimed to quantify the contribution of root-respired CO2 to both soil CO2 efflux and xylem CO2 transport by manipulating the autotrophic component of belowground respiration. We compared soil CO2 efflux and the flux of root-respired CO2 transported in the Transpiration Stream in girdled and nongirdled 9-yr-old oak trees (Quercus robur) to assess the impact of a change in the autotrophic component of belowground respiration on both CO2 fluxes. Stem girdling decreased xylem CO2 concentration, indicating that belowground respiration contributes to the aboveground transport of internal CO2. Girdling also decreased soil CO2 efflux. These results confirmed that root respiration contributes to xylem CO2 transport and that failure to account for this flux results in inaccurate estimates of belowground respiration when efflux-based methods are used. This research adds to the growing body of evidence that efflux-based measurements of belowground respiration underestimate autotrophic contributions.
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transport of root respired co2 via the Transpiration Stream affects aboveground carbon assimilation and co2 efflux in trees
New Phytologist, 2013Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Summary Upward transport of CO2 via the Transpiration Stream from belowground to aboveground tissues occurs in tree stems. Despite potentially important implications for our understanding of plant physiology, the fate of internally transported CO2 derived from autotrophic respiratory processes remains unclear. We infused a 13CO2-labeled aqueous solution into the base of 7-yr-old field-grown eastern cottonwood (Populus deltoides) trees to investigate the effect of xylem-transported CO2 derived from the root system on aboveground carbon assimilation and CO2 efflux. The 13C label was transported internally and detected throughout the tree. Up to 17% of the infused label was assimilated, while the remainder diffused to the atmosphere via stem and branch efflux. The largest amount of assimilated 13C was found in branch woody tissues, while only a small quantity was assimilated in the foliage. Petioles were more highly enriched in 13C than other leaf tissues. Our results confirm a recycling pathway for respired CO2 and indicate that internal transport of CO2 from the root system may confound the interpretation of efflux-based estimates of woody tissue respiration and patterns of carbohydrate allocation.
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Transport of root-derived CO2 via the Transpiration Stream affects aboveground tree physiology
The EGU General Assembly, 2012Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Recent research on soil CO2 efflux has shown that belowground autotrophic respiration is largely underestimated using classical net CO2 flux measurements. Aubrey & Teskey (2009) found that in forest ecosystems a substantial portion of the CO2 released from root respiration remained within the root system and was transported aboveground in the stem via the Transpiration Stream. The magnitude of this upward movement of CO2 from belowground tissues suggested important implications for how we measure aboveand belowground respiration. If a considerable fraction of root-respired CO2 is transported aboveground, where it might be fixed in woody and leaf tissues, then we are routinely underestimating the amount of C needed to sustain belowground tissues.
M J Canny - One of the best experts on this subject based on the ideXlab platform.
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Tyloses and the Maintenance of Transpiration
Annals of Botany, 1997Co-Authors: M J CannyAbstract:During a study of Transpiration and embolism-formation in petioles of sunflower, tyloses were frequently observed in early metaxylem vessels. Tyloses were confined to the inner ends of the xylem arcs, remote from the phloem. Vessels in this position are especially vulnerable to embolism. All stages of the invasion of vessel lumens by xylem parenchyma cells were observed, from the early protuberance of a cell through a pit to the complete occlusion of the lumen by one to several cells. The lumen space not occupied by tyloses was seen both filled with xylem sap, or embolized and gas-filled. Thus, during the early stages of tylosis formation the vessel remained active in carrying the Transpiration Stream. Thin-walled vessels of the protoxylem or early metaxylem were not tylosed, but were squashed and disappeared. These observations are interpreted as evidence that vessels vulnerable to embolism are decommissioned and replaced by parenchyma tissue, while new and less vulnerable vessels are added to the xylem arcs at the cambial side. It is proposed that tylosis formation is triggered by the frequent embolization of the vulnerable vessels to give, ultimately, an incompressible tissue. Then tyloses would be necessary to preserve the tissue pressure which expresses water to refill embolisms in the remaining vessels, and maintain Transpiration, as explained by the compensating pressure theory of water transport. # 1997 Annals of Botany Company
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potassium cycling in helianthus ions of the xylem sap and secondary vessel formation
Philosophical Transactions of the Royal Society B, 1995Co-Authors: M J CannyAbstract:Recent work has shown that dyes travelling in the Transpiration Stream in dicotyledon leaves become concentrated in the vessels of the finest veins where water enters the symplast. Such concentrations are called sumps. Using X-ray microanalysis of frozen-planed Helianthus leaf tissues, this paper investigates whether natural ions in the Transpiration Stream behave similarly and become concentrated in the fine veins. The most abundant ion in the xylem sap was potassium (K): concentrations of up to ~ 200 mM were found in some vessels of some leaf veins. Occurrence of such high concentrations was irregular and unrelated to vein order, leaf age, time of day or Transpiration conditions. High K concentrations were not especially characteristic of the fine veins, and it appears that sumps are not formed (as with the dyes) by selective uptake of water to the symplast: absence of K sumps is probably the result of uptake of K by the cells surrounding the vessels. The origin of K was sought in the stem, where evidence was found that differentiating secondary vessel elements accumulate very high concentrations (~ 500 mM) of K, releasing it into mature open vessels when they mature themselves. I propose the hypothesis that the K in the leaf vessels is derived from the K of the maturing secondary vessel elements of the stem. It arrives irregularly because the vessel maturation is spasmodic and the destiny of the released K depends upon the particular downStream connections of the new vessel to leaf traces. I further propose that the K in the leaf veins is taken up by bundle sheath cells and phloem parenchyma cells, and part of it is returned via the phloem to the cambium of the stem where it may be used again to provide osmoticum in the expansion of newly differentiating secondary vessel elements. When high concentrations of ions are present in vessels that are embedded in tissues whose cell walls have non-zero reflection coefficients (low diffusivities), osmotic pressures would develop in them. Such pressures may counteract tensions in the xylem sap generated by Transpiration, and help to account for the small values of these tensions measured recently with the xylem-pressure probe.
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the Transpiration Stream in the leaf apoplast water and solutes
Philosophical Transactions of the Royal Society B, 1993Co-Authors: M J CannyAbstract:Flow of the Transpiration Stream in the lumen apoplast of the xylem appears hydrodynamically orthodox in being approximately described by the Hagen-Poiseuille Law, and by Murray's Law for branching pipes. Flow may be followed in the major (supply) veins by labelling the Stream with dye solutions. Progress of the dye in the Stream into the minor (distribution) veins is obscured by surrounding tissues. Observations of the spread of fluorescent tracers from these veins in living leaves gave results that have been seriously misinterpreted to present a false view of the cell wall apoplast. Microscopy of the stabilized water-soluble fluorescent tracers moving out of the minor veins has revealed that: (i) the dye is separated from the water by filtration through cell membranes, and the water moves through the symplast; and (ii) the dye diffuses in the cell wall apoplast at rates 1/100 to 1/10 000 the rate of diffusion in water. As a consequence of (i), high concentrations of dye build up at sites called sumps. In grasses these sumps may be in the intercellular spaces outside the xylem. In dicotyledons these sumps are within the small tracheary elements. In fact, flow in the lumen apoplast is flow through leaky tubes, and is inadequately described by the Hagen-Poiseuille Law. Leaky tubes have a critical radius, below which (for a given pressure gradient) flow cannot occur. As a consequence of this, a wedge of xylem made up of vessels of different radii acts as a unit to concentrate dye tracers in a sump at its apex. Sumps may also be formed by evaporation of the water in the Stream, especially at leaf margins. Investigations with the cryo-analytical scanning electron microscope of the natural ions of the Transpiration Stream reveal high concentrations of K, Cl, P and Ca in the Stream in all the sizes of vessel and vein of sunflower leaves. These high concentrations appear to be produced, not by the mechanisms responsible for the formation of sumps of dyes, but by some other processes, probably occurring in the stem. The absence of sump formation by ions at the places where dyes form sumps is probably due to the more rapid penetration of the ions through the cell membranes. Reasons for the discrepancy between these measurements of salt concentrations in the Stream and those obtained from sap expressed from leaves by pressure vessels are discussed. Implications of these facts for the design and interpretation of experiments with leaves are presented.
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transfusion tissue of pine needles as a site of retrieval of solutes from the Transpiration Stream
New Phytologist, 1993Co-Authors: M J CannyAbstract:SUMMARY The fluorescent tracers sulphorhodamine G (SR) and pyrene trisulphonate (PTS) were used to explore the functions of cells and tissues within the pine needle, following their progress after feeding through the Transpiration Stream. The distributions of tracer in the needles were stabilized for fluorescence microscopy by rapid freezing and freeze-substitution, and anhydrous embedding and sectioning. After short pulse + chase times (up to 2 h), SR and PTS accumulated at higher-than-xylem concentrations in the transfusion tracheids on the flanks of the vascular strand, but did not pass out through the endodermis. The accumulations occurred locally where the Transpiration water was separated from the tracers and passed into the symplast of the transfusion parenchyma and endodermis. After a 24 h water chase, SR had entered the symplast through the transfusion parenchyma, and spread through the endodermis and palisade. It is argued that this is evidence of active H+-ATPase systems lowering the external pH of the transfusion parenchyma, and characterizes these cells as scavenging cells similar to those found in the bundle sheath systems of legume leaves. The transport of SR through the endodermis and palisade is the first clear evidence that this tracer can also function as a symplastic tracer. The hypothesis that the transfusion parenchyma acts to scavenge solutes from the Transpiration Stream was tested by loading the Stream with [14C]aspartate and examining the subsequent distribution of 14C by dry autoradiography. After a pulse + chase of (0.75 + 3) h, 14C was found concentrated in the transfusion parenchyma, and at even higher levels in the Strasburger cells. It is proposed that major functions of the transfusion tissue of gymnosperms are (a) the concentrating of solutes from the Transpiration Stream and (b) the retrieval from the Stream of selected solutes that are returned to the phloem through the Strasburger cells, or forwarded through the endodermis to the palisade.
Robert O. Teskey - One of the best experts on this subject based on the ideXlab platform.
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stem girdling affects the quantity of co2 transported in xylem as well as co2 efflux from soil
New Phytologist, 2014Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Laura Agneessens, Lieven Van Meulebroek, Kathy SteppeAbstract:Summary There is recent clear evidence that an important fraction of root-respired CO2 is transported upward in the Transpiration Stream in tree stems rather than fluxing to the soil. In this study, we aimed to quantify the contribution of root-respired CO2 to both soil CO2 efflux and xylem CO2 transport by manipulating the autotrophic component of belowground respiration. We compared soil CO2 efflux and the flux of root-respired CO2 transported in the Transpiration Stream in girdled and nongirdled 9-yr-old oak trees (Quercus robur) to assess the impact of a change in the autotrophic component of belowground respiration on both CO2 fluxes. Stem girdling decreased xylem CO2 concentration, indicating that belowground respiration contributes to the aboveground transport of internal CO2. Girdling also decreased soil CO2 efflux. These results confirmed that root respiration contributes to xylem CO2 transport and that failure to account for this flux results in inaccurate estimates of belowground respiration when efflux-based methods are used. This research adds to the growing body of evidence that efflux-based measurements of belowground respiration underestimate autotrophic contributions.
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transport of root respired co2 via the Transpiration Stream affects aboveground carbon assimilation and co2 efflux in trees
New Phytologist, 2013Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Summary Upward transport of CO2 via the Transpiration Stream from belowground to aboveground tissues occurs in tree stems. Despite potentially important implications for our understanding of plant physiology, the fate of internally transported CO2 derived from autotrophic respiratory processes remains unclear. We infused a 13CO2-labeled aqueous solution into the base of 7-yr-old field-grown eastern cottonwood (Populus deltoides) trees to investigate the effect of xylem-transported CO2 derived from the root system on aboveground carbon assimilation and CO2 efflux. The 13C label was transported internally and detected throughout the tree. Up to 17% of the infused label was assimilated, while the remainder diffused to the atmosphere via stem and branch efflux. The largest amount of assimilated 13C was found in branch woody tissues, while only a small quantity was assimilated in the foliage. Petioles were more highly enriched in 13C than other leaf tissues. Our results confirm a recycling pathway for respired CO2 and indicate that internal transport of CO2 from the root system may confound the interpretation of efflux-based estimates of woody tissue respiration and patterns of carbohydrate allocation.
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Transport of root-derived CO2 via the Transpiration Stream affects aboveground tree physiology
The EGU General Assembly, 2012Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Recent research on soil CO2 efflux has shown that belowground autotrophic respiration is largely underestimated using classical net CO2 flux measurements. Aubrey & Teskey (2009) found that in forest ecosystems a substantial portion of the CO2 released from root respiration remained within the root system and was transported aboveground in the stem via the Transpiration Stream. The magnitude of this upward movement of CO2 from belowground tissues suggested important implications for how we measure aboveand belowground respiration. If a considerable fraction of root-respired CO2 is transported aboveground, where it might be fixed in woody and leaf tissues, then we are routinely underestimating the amount of C needed to sustain belowground tissues.
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assimilation of xylem transported 13c labelled co2 in leaves and branches of sycamore platanus occidentalis l
Journal of Experimental Botany, 2009Co-Authors: Mary Anne Mcguire, John D Marshall, Robert O. TeskeyAbstract:Previous reports have shown that CO2 dissolved in xylem sap in tree stems can move upward in the Transpiration Stream. To determine the fate of this dissolved CO2, the internal transport of respired CO2 at high concentration from the bole of the tree was simulated by allowing detached young branches of sycamore (Platanus occidentalis L.) to transpire water enriched with a known quantity of 13CO2 in sunlight. Simultaneously, leaf net photosynthesis and CO2 efflux from woody tissue were measured. Branch and leaf tissues were subsequently analysed for 13C content to determine the quantity of transported 13CO2 label that was fixed. Treatment branches assimilated an average of 35% (SE=2.4) of the 13CO2 label taken up in the treatment water. The majority was fixed in the woody tissue of the branches, with smaller amounts fixed in the leaves and petioles. Overall, the fixation of internally transported 13CO2 label by woody tissues averaged 6% of the assimilation of CO2 from the atmosphere by the leaves. Woody tissue assimilation rates calculated from measurements of 13C differed from rates calculated from measurements of CO2 efflux in the lower branch but not in the upper branch. The results of this study showed unequivocally that CO2 transported in xylem sap can be fixed in photosynthetic cells in the leaves and branches of sycamore trees and provided evidence that recycling of xylem-transported CO2 may be an important means by which trees reduce the carbon cost of respiration.
Mary Anne Mcguire - One of the best experts on this subject based on the ideXlab platform.
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stem girdling affects the quantity of co2 transported in xylem as well as co2 efflux from soil
New Phytologist, 2014Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Laura Agneessens, Lieven Van Meulebroek, Kathy SteppeAbstract:Summary There is recent clear evidence that an important fraction of root-respired CO2 is transported upward in the Transpiration Stream in tree stems rather than fluxing to the soil. In this study, we aimed to quantify the contribution of root-respired CO2 to both soil CO2 efflux and xylem CO2 transport by manipulating the autotrophic component of belowground respiration. We compared soil CO2 efflux and the flux of root-respired CO2 transported in the Transpiration Stream in girdled and nongirdled 9-yr-old oak trees (Quercus robur) to assess the impact of a change in the autotrophic component of belowground respiration on both CO2 fluxes. Stem girdling decreased xylem CO2 concentration, indicating that belowground respiration contributes to the aboveground transport of internal CO2. Girdling also decreased soil CO2 efflux. These results confirmed that root respiration contributes to xylem CO2 transport and that failure to account for this flux results in inaccurate estimates of belowground respiration when efflux-based methods are used. This research adds to the growing body of evidence that efflux-based measurements of belowground respiration underestimate autotrophic contributions.
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transport of root respired co2 via the Transpiration Stream affects aboveground carbon assimilation and co2 efflux in trees
New Phytologist, 2013Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Summary Upward transport of CO2 via the Transpiration Stream from belowground to aboveground tissues occurs in tree stems. Despite potentially important implications for our understanding of plant physiology, the fate of internally transported CO2 derived from autotrophic respiratory processes remains unclear. We infused a 13CO2-labeled aqueous solution into the base of 7-yr-old field-grown eastern cottonwood (Populus deltoides) trees to investigate the effect of xylem-transported CO2 derived from the root system on aboveground carbon assimilation and CO2 efflux. The 13C label was transported internally and detected throughout the tree. Up to 17% of the infused label was assimilated, while the remainder diffused to the atmosphere via stem and branch efflux. The largest amount of assimilated 13C was found in branch woody tissues, while only a small quantity was assimilated in the foliage. Petioles were more highly enriched in 13C than other leaf tissues. Our results confirm a recycling pathway for respired CO2 and indicate that internal transport of CO2 from the root system may confound the interpretation of efflux-based estimates of woody tissue respiration and patterns of carbohydrate allocation.
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Transport of root-derived CO2 via the Transpiration Stream affects aboveground tree physiology
The EGU General Assembly, 2012Co-Authors: Jasper Bloemen, Robert O. Teskey, Mary Anne Mcguire, Doug P. Aubrey, Kathy SteppeAbstract:Recent research on soil CO2 efflux has shown that belowground autotrophic respiration is largely underestimated using classical net CO2 flux measurements. Aubrey & Teskey (2009) found that in forest ecosystems a substantial portion of the CO2 released from root respiration remained within the root system and was transported aboveground in the stem via the Transpiration Stream. The magnitude of this upward movement of CO2 from belowground tissues suggested important implications for how we measure aboveand belowground respiration. If a considerable fraction of root-respired CO2 is transported aboveground, where it might be fixed in woody and leaf tissues, then we are routinely underestimating the amount of C needed to sustain belowground tissues.
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assimilation of xylem transported 13c labelled co2 in leaves and branches of sycamore platanus occidentalis l
Journal of Experimental Botany, 2009Co-Authors: Mary Anne Mcguire, John D Marshall, Robert O. TeskeyAbstract:Previous reports have shown that CO2 dissolved in xylem sap in tree stems can move upward in the Transpiration Stream. To determine the fate of this dissolved CO2, the internal transport of respired CO2 at high concentration from the bole of the tree was simulated by allowing detached young branches of sycamore (Platanus occidentalis L.) to transpire water enriched with a known quantity of 13CO2 in sunlight. Simultaneously, leaf net photosynthesis and CO2 efflux from woody tissue were measured. Branch and leaf tissues were subsequently analysed for 13C content to determine the quantity of transported 13CO2 label that was fixed. Treatment branches assimilated an average of 35% (SE=2.4) of the 13CO2 label taken up in the treatment water. The majority was fixed in the woody tissue of the branches, with smaller amounts fixed in the leaves and petioles. Overall, the fixation of internally transported 13CO2 label by woody tissues averaged 6% of the assimilation of CO2 from the atmosphere by the leaves. Woody tissue assimilation rates calculated from measurements of 13C differed from rates calculated from measurements of CO2 efflux in the lower branch but not in the upper branch. The results of this study showed unequivocally that CO2 transported in xylem sap can be fixed in photosynthetic cells in the leaves and branches of sycamore trees and provided evidence that recycling of xylem-transported CO2 may be an important means by which trees reduce the carbon cost of respiration.
T. A. Mansfield - One of the best experts on this subject based on the ideXlab platform.
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the stomatal physiology of calcicoles in relation to calcium delivered in the xylem sap
Proceedings of The Royal Society B: Biological Sciences, 1994Co-Authors: D L R De Silva, T. A. MansfieldAbstract:Physiological mechanisms in calcicoles in simulated highly calcareous habitats have been investigated using Campanula glomerata, Centaurea scabiosa and Leontodon hispidus. Diffusion resistance of the leaves was unaffected by high concentrations (15 mol m$^{-3}$) of rhizospheric calcium in all three species, and in C. scabiosa and L. hispidus there was no inhibition of leaf extension even at 20 mol m$^{-3}$. Free calcium concentrations in samples of xylem sap taken from the roots were found to be very close to those in the rhizosphere. However, stomata on isolated epidermis of C. scabiosa and L. hispidus closed in response to elevated free calcium in the same manner as those of Commelina communis, a calcium-neutral plant. It is concluded that the calcicoles must possess an efficient mechanism to remove high concentrations of free calcium delivered into the leaf's apoplast by the Transpiration Stream. If the xylem sap reached the apoplast around the stomata containing even 5-10% of its free calcium, stomatal function would be disturbed. If these species are representative of calcicoles in general, the leaf's mechanism for preventing excess calcium from reaching the stomatal guard cells may be indispensable. The capacity to remove or sequester most of the calcium delivered in the xylem may be a key factor in determining whether a plant is a calcicole or not.
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the Transpiration Stream introduction
Philosophical Transactions of the Royal Society B, 1993Co-Authors: T. A. Mansfield, W J Davies, R A LeighAbstract:An inevitable consequence of their assimilation of carbon dioxide is the loss of water from aerial parts of plants. Leaves have a very low water content compared with the rate at which water can be lost into dry air. If they are to avoid damaging water deficits, which can develop within a few minutes, they must not only have a way of controlling water loss, but also have a means of ensuring rapid replacement of any water that is lost. The existence of tall land plants became possible only after a vascular system evolved which permitted rapid conduction of sufficient water from roots to shoots. Stephen Hales in Essays in vegetable statics in 1727 first proved experimentally that the ascending Transpiration Stream flows through the woody part of the stem. Figure 1 is a copy of Hales’ own illustration for which Strasburger et al . (1903) offered this explanation: At Z in the branch b all the tissues external to the slender wood have been removed. Since the leaves of this branch remain as fresh as those of the branch c , it is evident that the Transpiration current must pass through the wood and not through the cortical tissues. On the other hand, when a short length of the wood is removed from a stem, without at the same time unduly destroying the continuity of the bark, the leaves above the point of removal will droop as quickly as a twig cut off from the stem.
