共查询到20条相似文献,搜索用时 46 毫秒
1.
P. Guicherd J. P. Peltier E. Gout R. Bligny G. Marigo 《Trees - Structure and Function》1997,11(3):155-161
In leaves of Fraxinus excelsior L., malate and mannitol were characterized by 13C NMR spectroscopy and enzymatic specific assays as the major constituents of a soluble carbon fraction involved in an osmotic
adjustment. During a summer drought where predawn leaf water potential of adult trees growing in a mesoxerophilic stand fell
to – 4 MPa in August, malate and mannitol leaf contents increased by a factor of 1.8 and 2.2 respectively, compared to control
trees growing on a flood plain. This drought stress led to concentrations as high as 280 mM and 600 mM for mannitol and malate,
respectively. The effects of gradually developing water deficit were also studied in a semi-controlled environment in 3-year-old
seedlings. When predawn leaf water potential reached -6 MPa, leaves displayed a low turgor pressure but stomatal conductance
was still measurable. Malate and mannitol were also the main osmoticum involved. After rewatering, gas exchange capacities
were largely restored. Altogether, these results show that the strong water-stress tolerance of Fraxinus excelsior is in part related to an accumulation of malate and mannitol.
Received: 3 January 1996 / Accepted: 19 March 1996 相似文献
2.
During the extreme 1992–1997 El Niño drought event, widespread stem mortality, or tree dieback, of both mature and juvenile eucalypts occurred within the tropical savannas of northeast Australia. Most of the dieback occurred in individuals of the ironbark species complex (Eucalyptus crebra – E. xanthoclada) while individuals of the bloodwood species Corymbia erythrophloia, exhibited significantly less stem mortality. Indicative of greater water stress, predawn and midday xylem water potentials of ironbark adults and saplings were significantly more negative than predawn values of bloodwoods. The very negative xylem water potentials in ironbarks suggest that stem mortality in both adult and juvenile ironbarks results from drought-induced embolism and that ironbarks perhaps have a shallower and less extensive root system than bloodwoods. Although predawn and midday water potentials for ironbark adults and saplings were similar, a census of mature and juvenile ironbark trees indicated that mortality was higher in adult trees. Cavitation vulnerability curves indicated that ironbark saplings may be better buffered against cavitation than adult trees. If they possess smaller root systems, saplings are more likely than adults to experience low xylem water potentials, even in non-drought years. Xylem conduits produced in adult trees during periods of normal rainfall, although perhaps more efficient in water conduction, may be more vulnerable to cavitation during infrequent severe droughts. 相似文献
3.
Seasonal change in the δ2H content of water from twig sap, soil, rainfall and groundwater were measured to determine the water sources accessed by
jarrah (Eucalyptus marginata) trees at three sites in Western Australia with differing soils and depths to water table. During winter and spring the main
contributor to the water uptake of the trees was stored water in the surface layers of the soil replenished by predominantly
winter rainfall. With the onset of summer drought jarrah became more reliant on water from deeper down the profile. There
was no clear evidence that jarrah could tap water from groundwater more than 14 m deep in deep sands. Defining the source
of water for trees in deep lateritic soils using stable isotopes is hampered by the uniform deuterium profiles down most of
the unsaturated zone and into the groundwater. There was a limited response in the δ2H values of sapwater in twigs to changes in the δ2H of the upper layers of the deep sand following input of rainfall in autumn. The damped response was related to the small
variation in the δ2H composition of rainfall in most events during the year and the mixing in the tree of water extracted from different locations
in the soil profile.
Received: 21 August 1995 / Accepted: 3 December 1995 相似文献
4.
Marion Zapater Christian Hossann Nathalie Br��da Claude Br��chet Damien Bonal Andr�� Granier 《Trees - Structure and Function》2011,25(5):885-894
Hydraulic lift (HL) by tree roots in a young, broad-leaved, mixed temperate European forest was investigated during the 2008
growing season by injecting 18O-enriched soil water at a depth of 75–90 cm under drought conditions experimentally imposed in a rain-exclusion system. Based
on sap flow, leaf water potential, 2-D root distribution measurements, soil isotope profiles, and xylem water isotope composition,
water acquisition and use by two tree species, beech (Fagus sylvatica) and oak (Quercus petraea) was compared. We showed that, unlike oak, beech experienced a marked decrease in sap flow and predawn leaf water potential
with increasing soil drought. This behaviour was logical considering the shallower root system in beech than in oak. Six days
after 18O-labelling, we observed isotopic enrichment in the shallower soil layers. Since the intermediate soil layers did not display
any enrichment, our results clearly pointed to hydraulic lift by tree roots. The superficial enrichment that was observed
in the vicinity of oak trunks and the increase in the isotopic signature of xylem sap in the oak trees but not in the beech
trees confirmed the predominant role of oak in the hydraulic lift at our site. Even though facilitation for water acquisition
among species was not observed here, our results suggest a potential positive contribution of species like oak toward maintaining
species diversity in mixed forest ecosystems submitted to severe drought events. 相似文献
5.
Sap flow as an indicator of transpiration and the water status of young apricot trees 总被引:15,自引:0,他引:15
Alarcón J.J. Domingo R. Green S.R. Sánchez-Blanco M.J. Rodríguez P. Torrecillas A. 《Plant and Soil》2000,227(1-2):77-85
The relationship between water loss via transpiration and stem sap flow in young apricot trees was studied under different
environmental conditions and different levels of soil water status. The experiment was carried out in a greenhouse over a
2-week period (November 2–14, 1997) using three-year-old apricot trees (Prunus armeniaca cv. Búlida) growing in pots. Diurnal courses of leaf water potential, leaf conductance and leaf turgor potential also were
recorded throughout the experiment. Data from four days of different enviromental conditions and soil water availability have
been selected for analysis. On each of the selected days the leaf water potential and the mean transpiration rates were well
correlated. The slope of the linear regression of this correlation, taken to indicate the total hydraulic resistance of the
tree, confirmed an increasing hydraulic resistance under drought conditions. When the trees were not drought stressed the
diurnal courses of sap flow and transpiration were very similar. However, when the trees were droughted, measured of sap flow
slightly underestimated actual transpiration. Our heat-pulse measurements suggest the amount of readily available water stored
in the stem and leaf tissues of young apricot trees is sufficient to sustain the peak transpiration rates for about 1 hour.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
"Cavitation fatigue" is the increased susceptibility of a xylem conduit to cavitation as a result of its prior cavitation. It was investigated whether cavitation fatigue induced in vivo could be repaired in intact plants. Sunflowers (Helianthus annuus L.) were subjected to soil drought in the greenhouse. Native embolism and vulnerability to cavitation was measured in well-watered controls and after 5 d and 10 d of controlled drought. A dramatic cavitation fatigue was observed where droughted xylem that was refilled in the laboratory developed up to 60 PLC (percentage loss of hydraulic conductivity) at -1 MPa versus only 5.2 PLC in non-droughted controls. Rewatered plants showed the complete reversal of cavitation fatigue over 4 d. Reversal of fatigue was correlated with the refilling of embolized vessels in the intact plants (r(2)=0.91, P<0.01), suggesting that xylem transport to fatigued vessels was required for their repair. The in vivo reversal of fatigue was partially duplicated in excised stem segments by perfusing them with root exudates from droughted (DR) and well-watered (WW) plants. The DR exudate had a greater effect, and this was associated with a greater pH in the DR versus WW saps, but there was no difference in total cation concentration. Perfusions with 2 mM CaCl(2) and KCl solutions also partially reversed cavitation fatigue as opposed to no effect with deionized water, suggesting a role of ions in addition to a pH effect. It is suspected that fatigue is caused by stretching and partial disruption of linkages between cellulose microfibrils in inter-conduit pit membranes during air seeding, and that the reversal of fatigue involves restoring these linkages by ingredients in xylem sap. 相似文献
7.
Cavitation fatigue. Embolism and refilling cycles can weaken the cavitation resistance of xylem 总被引:11,自引:0,他引:11
Although cavitation and refilling cycles could be common in plants, it is unknown whether these cycles weaken the cavitation resistance of xylem. Stem or petiole segments were tested for cavitation resistance before and after a controlled cavitation-refilling cycle. Cavitation was induced by centrifugation, air drying of shoots, or soil drought. Except for droughted plants, material was not significantly water stressed prior to collection. Cavitation resistance was determined from "vulnerability curves" showing the percentage loss of conductivity versus xylem pressure. Two responses were observed. "Resilient" xylem (Acer negundo and Alnus incana stems) showed no change in cavitation resistance after a cavitation-refilling cycle. In contrast, "weakened" xylem (Populus angustifolia, P. tremuloides, Helianthus annuus stems, and Aesculus hippocastanum petioles) showed considerable reduction in cavitation resistance. Weakening was observed whether cavitation was induced by centrifugation, air dehydration, or soil drought. Observations from H. annuus showed that weakening was proportional to the embolism induced by stress. Air injection experiments indicated that the weakened response was a result of an increase in the leakiness of the vascular system to air seeding. The increased air permeability in weakened xylem could result from rupture or loosening of the cellulosic mesh of interconduit pit membranes during the water stress and cavitation treatment. 相似文献
8.
Wood diameter indicates diurnal and long-term patterns of xylem water potential in Norway spruce 总被引:6,自引:0,他引:6
The stem diameter of adult Norway spruce trees was measured to see whether changes in xylem water potential lead to detectable radial deformation of the wood. The dendrometers used in these experiments measured only the dimensional changes of the woody cylinder (sap- and heartwood). Wood diameter was measured close to the ground and just below the living crown. After correction for thermal expansion of dendrometers and wood, diurnal variation of wood diameter ranged between 50 and 180 µm. Psychrometric measurements showed that xylem water potential varied in parallel to wood diameter. Diameter changes were always more pronounced at the higher stem position and exhibited a clear diurnal pattern. During the day, wood diameter decreased with increasing vapor pressure deficit and transpiration rate and with decreasing twig water potential. At night, the wood re-expanded but did not always reach the dimension of the previous day. Pre-dawn wood diameter decreased during periods of soil drought, a process which rapidly stopped and reversed after rain events. On several days, oscillation in wood diameter was observed during the mid-day hours. The oscillation had a period of approximately 50 min and showed a phase shift between different stem heights. All observed patterns of wood shrinkage and expansion were consistent with the hypothesis that xylem water tension leads to an elastic contraction of xylem conduits. The results demonstrate that xylem diameter is more suitable than whole-stem diameter for monitoring changes in xylem water potential. 相似文献
9.
10.
Significance and limits in the use of predawn leaf water potential for tree irrigation 总被引:5,自引:1,他引:4
Améglio Thierry Archer Philippe Cohen Moisés Valancogne Charles Daudet François-alain Dayau Sylvia Cruiziat Pierre 《Plant and Soil》1999,207(2):155-167
Research in estimating the water status of crops is increasingly based on plant responses to water stress. Several indicators
can now be used to estimate this response, the most widely available of which is leaf water potential (ΨLWP) as measured with a pressure chamber. For many annual crops, the predawn leaf water potential (ΨPLWP), assumed to represent the mean soil water potential next to the roots, is closely correlated to the relative transpiration
rate, RT. A similar correlation also holds for young fruit trees grown in containers. However, exceptions to this rule are
common when soil water content is markedly heterogeneous.
Two experimental conditions were chosen to assess the validity of this correlation for heterogeneous soil water content: 1)
young walnut trees in split-root containers. The heterogeneity was created by two unequal compartments (20% and 80% of total
volume), of which only the smaller was irrigated and kept at a moisture content higher than field capacity (permanent drainage).
2) adult walnut trees in an orchard. In this case, soil water heterogeneity was achieved by limiting the amount of localised
irrigation (20% of the irrigated control)
which was applied every evening.
Values of sap flux and of minimum and predawn leaf water potentials with homogeneous and heterogeneous soil water content
were compared for trees grown in the orchard and in containers. In spite of intense drought reflected by very low RT or stem
water potential, ΨPLWP of trees under heterogeneous moisture conditions remained high (between -0.2 and -0.4 MPa) both in the orchard and in containers.
These values were higher than those usually considered critical under homogeneous soil conditions. A semi-quantitative model,
based on the application of Ohm's analogy to split-root conditions, is proposed to explain the apparently conflicting results
in the literature on the relation between ΨPLWP and soil water potential.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
The canopy water relations of old-growth Douglas-fir trees 总被引:4,自引:0,他引:4
W. L. Bauerle T. M. Hinckley J. Cermak J. Kucera K. Bible 《Trees - Structure and Function》1999,13(4):211-217
We investigated whole tree water relations in 56–65 m tall, old-growth Pseudotsuga menziesii trees within the Wind River Canopy Crane site, Carson, Washington, USA. We measured at predawn and solar noon the vertical
gradients in xylem pressure potential using a pressure chamber. On an Abies amabilis sapling located in the understory at the base of one of the study trees, predawn and solar noon xylem pressure potentials
were also measured. Xylem pressure potential data were measured from late June through early September 1996 on foliage sampled
from 1 to 64.5 m. Over this height gradient, predawn water potentials ranged from –0.23 to –1.10 MPa. Solar noon values showed
an even greater range (from –0.44 to –2.51 MPa). At predawn, the water potential gradient approached the theoretical hydrostatic
gradient (–0.0105 vs –0.010 MPa m–1). The gradient at solar noon was steeper (–0.0331 MPa m–1). Instantaneous stomatal conductances were not greatly different between young, sapling-sized and old-growth trees [0.094±0.033
(SD) vs 0.086±0.045 cm s–1, respectively]. Stomata of both size classes of trees appeared very sensitive to increasing vapor pressure deficits. A comparison
of stable carbon isotope values from the old-growth and sapling-sized trees indicated lower stomatal conductances in the old-growth.
This study provides sound documentation regarding the utility of the cohesion theory in the interpretation of water potential
gradients. This study also emphasizes inherent differences between sapling-sized and tall, old-growth trees.
Received: 10 January 1998 / Accepted: 12 October 1998 相似文献
12.
Drought-induced changes in xylem pH, ionic composition, and ABA concentration act as early signals in field-grown maize (Zea mays L.). 总被引:4,自引:0,他引:4
Andi Bahrun Christian R Jensen Folkard Asch Vagn O Mogensen 《Journal of experimental botany》2002,53(367):251-263
Early signals potentially regulating leaf growth and stomatal aperture in field-grown maize (Zea mays L.) subjected to drought were investigated. Plants grown in a field lysimeter on two soil types were subjected to progressive drought during vegetative growth. Leaf ABA content, water status, extension rate, conductance, photosynthesis, nitrogen content, and xylem sap composition were measured daily. Maize responded similarly to progressive drought on both soil types. Effects on loam were less pronounced than on sand. Relative to fully-watered controls, xylem pH increased by about 0.2 units one day after withholding irrigation (DAWI) and conductivity decreased by about 0.25 mS cm(-1) 1-3 DAWI. Xylem nitrate, ammonium, and phosphate concentrations decreased by about 50% at 1-5 DAWI and potassium concentration decreased by about 50% at 7-8 DAWI. Xylem ABA concentration consistently increased by 45-70 pmol ml(-1) at 7 DAWI. Leaf extension rate decreased 5 DAWI, after the changes in xylem chemical composition had occurred. Leaf nitrogen significantly decreased 8-16 DAWI in droughted plants. Midday leaf water potential and photosynthesis were significantly decreased in droughted plants late in the drying period. Xylem nitrate concentration was the only ionic xylem sap component significantly correlated to increasing soil moisture deficit and decreasing leaf nitrogen concentration. Predawn leaf ABA content in droughted plants increased by 100-200 ng g(-1) dry weight at 7 DAWI coinciding with a decrease in stomatal conductance before any significant decrease in midday leaf water potential was observed. Based on the observed sequence, a chain of signal events is suggested eventually leading to stomatal closure and leaf surface reduction through interactive effects of reduced nitrogen supply and plant growth regulators under drought. 相似文献
13.
Predawn disequilibrium between plant and soil water potentials in two cold-desert shrubs 总被引:15,自引:0,他引:15
L. A. Donovan D. J. Grisé J. B. West R. A. Pappert N. N. Alder J. H. Richards 《Oecologia》1999,120(2):209-217
Classical water relations theory predicts that predawn plant water potential should be in equilibrium with soil water potential
(soil Ψw) around roots, and many interpretations of plant water status in natural populations are based on this expectation. We examined
this expectation for two salt-tolerant, cold-desert shrub species in glasshouse experiments where frequent watering assured
homogeneity in soil Ψw and soil-root hydraulic continuity and where NaCl controlled soil Ψw. Plant water potentials were measured with a pressure chamber (xylem Ψp) and thermocouple psychrometers (leaf Ψw). Soil Ψw was measured with in situ thermocouple psychrometers. Predawn leaf Ψw and xylem Ψp were significantly more negative than soil Ψw, for many treatments, indicating large predawn soil-plant Ψw disequilibria: up to 1.2 MPa for Chrysothamnus nauseosus (0 and 100 mm NaCl) and 1.8 MPa for Sarcobatus vermiculatus (0, 100, 300, and 600 mm NaCl). Significant nighttime canopy water loss was one mechanism contributing to predawn disequilibrium, assessed by comparison
of xylem Ψp for bagged (to minimize transpiration) and unbagged canopies, and by gas exchange measurements. However, nighttime transpiration
accounted for only part of the predawn disequilibrium. Other mechanisms that could act with nighttime transpiration to generate
large predawn disequilibria are described and include a model of how leaf apoplastic solutes could contribute to the phenomenon.
This study is among the first to conclusively document such large departures from the expectation of predawn soil-plant equilibrium
for C3 shrubs, and provides a general framework for considering relative contributions of nighttime transpiration and other plant-related
mechanisms to predawn disequilibrium.
Received: 12 November 1998 / Accepted: 5 May 1999 相似文献
14.
Hydraulic Lift in Cork Oak Trees in a Savannah-Type Mediterranean Ecosystem and its Contribution to the Local Water Balance 总被引:3,自引:1,他引:2
Cathy Kurz-Besson Dennis Otieno Raquel Lobo do Vale Rolf Siegwolf Markus Schmidt Alastair Herd Carla Nogueira Teresa Soares David Jorge Soares David John Tenhunen João Santos Pereira Manuela Chaves 《Plant and Soil》2006,282(1-2):361-378
The aim of this study was to identify the sources and depth of water uptake by 15-years old Quercus suber L. trees in southern Portugal under a Mediterranean climate, measuring δ18O and δD in the soil–plant-atmosphere continuum. Evidence for hydraulic lift was substantiated by the daily fluctuations observed
in Ψs at 0.4 and 1 m depth and supported by similar δ18O values found in tree xylem sap, soil water in the rhizosphere and groundwater. From 0.25 m down to a depth of 1 m, δD trends
differed according to vegetation type, showing a more depleted value in soil water collected under the evergreen trees (−47‰)
than under dead grasses (−35‰). The hypothesis of a fractionation process occurring in the soil due to diffusion of water
vapour in the dry soil is proposed to explain the more depleted soil δD signature observed under trees. Hydraulically lifted
water was estimated to account for 17–81% of the water used during the following day by tree transpiration at the peak of
the drought season, i.e., 0.1–14 L tree−1 day−1. Significant relationships found between xylem sap isotopic composition and leaf water potential in early September emphasized
the positive impact of the redistribution of groundwater in the rhizosphere on tree water status. 相似文献
15.
Leaf gas exchange and stem xylem hydraulic and mechanical properties were studied for unburned adults and resprouting burned
Juglans californica (southern California black walnut) trees 1 year after a fire to explore possible trade-offs between mechanical and hydraulic
properties of plants. The CO2 uptake rates and stomatal conductance were 2–3 times greater for resprouting trees than for unburned adults. Both predawn
and midday water potentials were more negative for unburned adult trees, indicating that the stems were experiencing greater
water stress than the stems of resprouting trees. In addition, the xylem specific conductivity was similar in the two growth
forms, even though the stems of resprouting trees were less vulnerable to water-stress-induced embolism than similar diameter,
but older, stems of adult trees. The reduced vulnerability may have been due to less cavitation fatigue in stems of resprouts.
The modulus of elasticity, modulus of rupture and xylem density were all greater for resprouts, indicating that resprouts
have greater mechanical strength than do adult trees. The data suggest that there is no trade-off between stem mechanical
strength and shoot hydraulic and photosynthetic efficiency in resprouts, which may have implications for the success of this
species in the fire-prone plant communities of southern California. 相似文献
16.
Interpretation of seasonal changes of xylem embolism and plant hydraulic resistance in Fagus sylvatica 总被引:6,自引:1,他引:5
The annual course of xylem embolism in twigs of adult beech trees was monitored, and compared to concurrent changes of tree water status and hydraulic resistances. Xylem embolism was quantified in 1-year-old apical twigs by the hydraulic conductivity as a percentage of the maximum measured after removal of air emboli. Tree and root hydraulic resistances were estimated from water potential differences and sap flux measurements. The considerable degree of twig embolism found in winter (up to 90% loss of hydraulic conductivity) may be attributed to the effect of freeze-thaw cycles in the xylem. A partial recovery from winter embolism occurred in spring, probably because of the production of new functional xylem. Xylem embolism fluctuated around 50% throughout the summer, without significant changes. Almost complete refilling of apical twigs was observed early in autumn. A significant negative correlation was found between xylem embolism and precipitation; thus, an active role of rainfall in embolism reversion is hypothesized. Tree and root hydraulic resistances were found to change throughout the growing period. A marked decrease of hydraulic resistance preceded the refilling of apical twigs in the autumn. Most of the decrease in total tree resistance was estimated to be located in the root compartment. 相似文献
17.
Alexandros Beis Anastasios Zotos Angelos Patakas 《Environmental and Experimental Botany》2009,67(2):305-311
The effect of differences in applied pressure and time of sampling on pH values of xylem sap collected using the leaf pressurization technique was examined in two grapevine varieties originating from contrasting habitats (Vitis vinifera L., cvs. Sabatiano and Mavrodafni) after subjecting them to drought. Three fractions of xylem sap exudates were collected from each leaf according to differences in applied pressure; fractions (I), (II) and (III) corresponding to 1 MPa, 2 MPa and 2.5 MPa pressure, respectively. The pH values in fraction (I) were significantly lower than those in fractions (II) and (III). The sap pH values in fraction (III) seemed to better correspond to changes in leaf apoplastic pH. The time of sampling was found to strongly influence xylem pH values. In particular, a positive relationship between predawn xylem pH values and soil drying was observed. Conversely, xylem pH values measured later during the day (i.e. at 8:00, 9:00 and 10:00 am) were not significantly affected by the reduction in soil water availability in both varieties. It is suggested that the most suitable period for sap sampling in order to better discriminate drought effects on xylem sap pH is at predawn. Furthermore, there were significant differences in pH values as well as in the sensitivity of stomatal conductance to pH between the two varieties. These differences might be related to strategy differences between grapevine varieties for adaptation to drought. 相似文献
18.
Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance 总被引:2,自引:0,他引:2
NICOLAS MARC E.; SIMPSON RICHARD J.; LAMBERS HANS; DALLING MICHAEL J. 《Annals of botany》1985,55(5):743-754
A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 4060per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation 相似文献
19.
The functional xylem anatomy and the hydraulic conductivity of intact and treated branch junctions of the diffuse-porous
sugar maple (Acer saccharum Marsh.) were compared to those of the ring-porous black oak (Quercus velutina Lam.). Maple shoots possessed greater growth intensity than those of oak. The extensive growth of the maple trees resulted
in about a two-fold increase in xylem production in the maple branches. Branches were altered by removing a patch of bark
from the base of a branch (near a junction) leaving a bridge of bark on the upper or lower side of the branch. The experimentally
treated branch junctions revealed that, in oak, most (up to 92%) of the water flows in the lower side of a branch, where most
of the large vessels occurred. In maple, most of the conductive tissue was observed to form in the upper side of the branches,
which was equally or more conductive than the lower side. A treatment of longitudinal, parallel scratches in the bark-bridge,
which reduced earlywood vessel width, substantially decreased conductivity (to only 15%) in oak, but had no effect on conductivity
in maple. In maple, such wounding stimulated more wood formation and increased conductivity. In both trees, a narrow bridge
at the junction induced more wood formation and higher conductivity in the branch. The mechanisms controlling wood formation
and water flow in branch junctions of ring- and diffuse-porous trees are discussed.
Received: 14 February 1996 / Accepted: 27 May 1996 相似文献
20.
Involvement of malate and mannitol in the diurnal regulation of the water status in members of Oleaceae 总被引:1,自引:0,他引:1
This study examines water status regulation in plants of the Oleaceae family and in some other co-occurring species that
are exposed to high solar radiation, in the same habitat. Fraxinus excelsior L., one of the most studied Oleaceae in this field exhibited, during the growing season, a close relationship between diurnal
variations in leaf water potential and changes in malate, mannitol and K+ levels, depending on the weather conditions. On sunny days, similar variations can be observed in leaves of the other Oleaceae, with a concomitant decrease in the osmotic potential between predawn and solar noon. Malate, mannitol and the well-known
osmoticum K+, contribute greatly to the osmotic potential decrease. This mechanism, which can be related to the osmotic adjustment described
for both drought and salt-affected plants, appears as a general response in plants of the Oleaceae family. Among the other
co-occurring species investigated, only Quercus robur L. displayed a similar mechanism under the same environmental conditions, but two other organic compounds, quinic and shikimic
acids, are presumably involved. Alnus glutinosa (L.) Gaertn. and Robinia pseudacacia L. responded to a vapor deficit by partial stomatal closure, as transpiration progressed through the morning.
Received: 19 December 1996 / Accepted: 17 February 1997 相似文献