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1.
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
2.
Water and Nutrient Dynamics in Surface Roots and Soils are not Modified by Short-term Flooding of Phreatophytic Plants in a Hyperarid Desert 总被引:3,自引:0,他引:3
Fanjiang Zeng Timothy M. Bleby Peter A. Landman Mark A. Adams Stefan K. Arndt 《Plant and Soil》2006,279(1-2):129-139
Little is known of the mechanisms employed by woody plants to acquire key resources such as water and nutrients in hyperarid
environments. For phreatophytic plants, deep roots are necessary to access the water table, but given that most nutrients
in many desert ecosystems are stored in the upper soil layers, viable shallow roots may be equally necessary for nutrient
uptake. We sought to better understand the interaction between water and nutrient uptake from soil horizons differing in the
relative abundance of these resources. To this end, we monitored plant water and nutrient status before and after applying
flood irrigation to four phreatophytic perennial plant species in the remote hyperarid Taklamakan desert in western China.
Sap flow in the roots of five plants of the perennial desert species Alhagi sparsifolia Shap., Karelina caspica (Pall.) Less., Calligonum caput medusea Schrenk, and Eleagnus angustifolia Hill. was monitored using the heat ratio method (HRM). Additionally we measured predawn and midday water potential, foliar
nitrate reductase activity (NRA), xylem sap nutrient concentration and the concentration of total solutes in the leaves before,
12 and 96 h after flooding to investigate possible short-term physiological effects on water and nutrient status. Rates of
sap flow measured during the day and at night in the absence of transpiration did not change after flooding. Moderately high
rates of sap flow (HRM heat pulse velocity, 5–25 cm h−1) detected during the day in soils that had a near zero water content at the surface indicated that all species had contact
to groundwater. There was no evidence from sap flow data that plants had utilised flood water to increase maximum rates of
transpiration under similar climatic conditions, and there was no evidence of a process to improve the efficiency of water
or nutrient uptake, such as hydraulic redistribution (i.e. the passive movement of water from moist soil to very dry soil
via roots). Measurements of plant water status, xylem sap nutrient status, foliar NRA and the concentration of osmotically
active substances were also unaffected by flood irrigation. Our results clearly show that groundwater acts as the major source
of water and nutrients for these plants. The inability of plants to utilise abundant surface soil–water or newly available
nutrients following irrigation was attributed to the absence of fine roots in the topsoil layer. 相似文献
3.
Hydraulic redistribution in three Amazonian trees 总被引:13,自引:0,他引:13
About half of the Amazon rainforest is subject to seasonal droughts of 3 months or more. Despite this drought, several studies have shown that these forests, under a strongly seasonal climate, do not exhibit significant water stress during the dry season. In addition to deep soil water uptake, another contributing explanation for the absence of plant water stress during drought is the process of hydraulic redistribution; the nocturnal transfer of water by roots from moist to dry regions of the soil profile. Here, we present data on patterns of soil moisture and sap flow in roots of three dimorphic-rooted species in the Tapajós Forest, Amazônia, which demonstrate both upward (hydraulic lift) and downward hydraulic redistribution. We measured sap flow in lateral and tap roots of our three study species over a 2-year period using the heat ratio method, a sap-flow technique that allows bi-directional measurement of water flow. On certain nights during the dry season, reverse or acropetal flow (i.e.,in the direction of the soil) in the lateral roots and positive or basipetal sap flow (toward the plant) in the tap roots of Coussarea racemosa (caferana), Manilkara huberi (maçaranduba) and Protium robustum (breu) were observed, a pattern consistent with upward hydraulic redistribution (hydraulic lift). With the onset of heavy rains, this pattern reversed, with continuous night-time acropetal sap flow in the tap root and basipetal sap flow in lateral roots, indicating water movement from wet top soil to dry deeper soils (downward hydraulic redistribution). Both patterns were present in trees within a rainfall exclusion plot (Seca Floresta) and to a more limited extent in the control plot. Although hydraulic redistribution has traditionally been associated with arid or strongly seasonal environments, our findings now suggest that it is important in ameliorating water stress and improving rain infiltration in Amazonian rainforests. This has broad implications for understanding and modeling ecosystem process and forest function in this important biome. 相似文献
4.
Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO3: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO3: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis 相似文献
5.
The redistribution of soil water by tree root systems 总被引:29,自引:0,他引:29
Plant roots transfer water between soil layers of different water potential thereby significantly affecting the distribution
and availability of water in the soil profile. We used a modification of the heat pulse method to measure sap flow in roots
of Grevillea robusta and Eucalyptus camaldulensis and demonstrated a redistribution of soil water from deeper in the profile to dry surface horizons by the root system. This
phenomenon, termed “hydraulic lift” has been reported previously. However, we also demonstrated that after the surface soils
were rewetted at the break of season, water was transported by roots from the surface to deeper soil horizons – the reverse
of the “hydraulic lift” behaviour described for other woody species. We suggest that “hydraulic redistribution” of water in
tree roots is significant in maintaining root viability, facilitating root growth in dry soils and modifying resource availability.
Received: 26 January 1998 / Accepted: 15 April 1998 相似文献
6.
Jokhan Anjeela D.; Else Mark A.; Jackson Michael B. 《Journal of experimental botany》1996,47(10):1595-1599
Abscisic acid (ABA) moving from roots to shoots in the transpirationstream is a potential hormonal message integrating perceptionof a root stress with adaptive changes in the shoot. A twinroot system was used to study ways of estimating effects ofdroughting the upper roots of Ricinus communis L. on abscisicacid (ABA) transport to the shoot in the transpiration stream.Droughted plants transpired more slowly than controls. Droughtingalso increased concentrations of ABA up to I I-fold in sap inducedto flow from the roots of freshly decapitated plants at ratesof whole plant transpiration. However, because of dilution effectsarising from the different sap flows in control and droughtedplants, these changes in ABA concentration in the xylem sapdid not accurately reflect amounts of ABA transported. To overcomethis problem, delivery rates were calculated by multiplyingconcentration with sap flow rate to generate ABA delivery interms of µmol s1 per plant. Droughting for 24 hor more increased ABA delivery from roots to shoots by 5-fold.Since droughting can alter the relative sizes of the roots andshoots and also the root:shoot ratio these delivery rates wererefined in several ways to reflect both the amount of root generatingthe ABA message and the size of the recipient shoot system. Key words: Abscisic acid, Ricinus communis L., soil drying, xylem sap 相似文献
7.
Xylem conduction and cavitation in Hevea brasiliensis 总被引:2,自引:0,他引:2
Clones of Hevea were studied in an attempt to discover the reasonsfor differences in the hydraulic performance of xylem. Differencesbetween clones were determined, including hydraulic conductivityand conduit width and length distributions. However, it hasproved difficult to reconcile anatomical differences with physiologicalperformance for use in future plant breeding programmes. When leaf relative water content (RWC) had been reduced fromabout 95% to 85%, the hydraulic conductivity of petioles decreasedsharply to about 40% of the initial value. This value correspondedwith xylem sap tensions of 1.82.0 MPa. Acoustic detectionexperiments revealed that this reduction in hydraulic conductivitycoincided with the greatest occurrence of cavitation. It seemsinescapable that the reduction in hydraulic conductivity wascaused by embolization; thereafter gas bubbles blocked the flowof water inside many of the conduits. There was some indicationthat eventually such bubbles might be dissolved, because thehydraulic conductivity increased again if specimens were fullyrehydrated. Apparently, the incidence of cavitation coincides with the entryof gas bubbles via ultramicroscopic pores into the conduitsthrough the walls according to the air-seeding hypothesis. Whena petiolate leaf is tested in a pressure chamber it is impossibleto make satisfactory measurements of a balancing pressure beyondc. 1.82.0 MPa, because air bubbles, mixed with sap andescaping from the conduits, form a persistent froth. Xylem transportin Hevea seems to be disrupted relatively easily under waterstress which is a feature of other tropical species adaptedto rainforesttype environments Key words: Hevea, xylem, cavitation, conduit, hydraulic conductivity 相似文献
8.
Xylem sap of sinker (tap) root, cluster feeding roots, lateral roots and from an age series of main stem extensions of 6-year trees of Banksia prionotes was collected and analyzed for principal organic and inorganic solutes. During the phase of root uptake activity in winter and spring, cluster roots were principal xylem donors of malate, phosphate, chloride, sodium, potassium and amino acid N whereas other parts of the root served as major sources to the shoot of other cations, nitrate and sulphate. Sinker root xylem sap was at all times less concentrated in solutes than that of lateral roots into which cluster roots were voiding exported solutes. Phosphate was abstracted from xylem by stem tissue during winter and it and a range of other solutes released back to xylem immediately prior to extension growth of the shoot in summer. Phloem sap collected from mid regions of stems was unusually low in potassium and phosphate relative to chloride and sulphate in comparison with phloem sap of other species, and its low potassium: sodium ratio relative to xylem indicated poor discrimination against sodium during phloem loading. Data are discussed in relation to the asynchronous seasonal cycles of nutrient uptake and shoot growth. 相似文献
9.
《Environmental and Experimental Botany》2003,49(3):201-208
We studied the tree access to deep water sources and the possibility of hydraulic lift from the deep roots of a Pinus nigra tree to the shallow soil layers in a Mediterranean forest of NE Spain. We also studied the use of hydraulically lifted water by neighboring trees, shrubs, and sprouts. We enriched the roots of a large P. nigra (10 m tall) with deuterium by accessing them from a below ground cave. During the next 3 days we measured stable deuterium isotopic composition of xylem sap, shoot predawn and midday water potentials, and the leaf δ13C and δ15N of the P. nigra tree, neighboring Quercus ilex ballota trees and sprouts, and Juniperus oxycedrus shrubs. The study was conducted both in dry summer and in wet spring. In summer, deuterated water absorbed by deep roots of P. nigra appeared in the stem water of neighboring plants and in surface soil. The most δD-enriched plant xylem sap was found in the enriched P. nigra tree, followed by the Q. ilex sprouts, the small Q. ilex trees and the surface soil (15 cm). All these trends disappeared in the wet spring season, when HDO only slightly appeared in the surface soil. The results show that the studied P. nigra tree accesses deep water source and conducts hydraulic lift in this Mediterranean forest in dry summer but not necessarily in wet spring. 相似文献
10.
Nadezhda Nadezhdina Maria Isabel Ferreira Rodolfo Silva Carlos Arruda Pacheco 《Plant and Soil》2008,305(1-2):105-119
Hydraulic redistribution (HR) is the phenomenon where plant roots transfer water between soil horizons of different water
potential. When dry soil is a stronger sink for water loss from the plant than transpiration, water absorbed by roots in wetter
soil horizons is transferred toward, and exuded into dry soil via flow reversals through the roots. Reverse flow is a good
marker of HR and can serve as a useful tool to study it over the long-term. Seasonal variation of water uptake of a Quercus suber tree was studied from late winter through autumn 2003 at Rio Frio near Lisbon, Portugal. Sap flow was measured in five small
shallow roots (diameter of 3–4 cm), 1 to 2 m from the tree trunk and in four azimuths and at different xylem depths at the
trunk base, using the heat field deformation method (HFD). The pattern of sap flow differed among lateral roots as soil dried
with constant positive flow in three roots and reverse flow in two other roots during the night when transpiration ceased.
Rain modified the pattern of flow in these two roots by eliminating reverse flow and substantially increasing water uptake
for transpiration during the day. The increase in water uptake in three other roots following rain was not so substantial.
In addition, the flux in individual roots was correlated to different degrees with the flux at different radial depths and
azimuthal directions in trunk xylem. The flow in outer trunk xylem seemed to be mostly consistent with water movement from
surface soil horizons, whereas deep roots seemed to supply water to the whole cross-section of sapwood. When water flow substantially
decreased in shallow lateral roots and the outer stem xylem during drought, water flow in the inner sapwood was maintained,
presumably due to its direct connection to deep roots. Results also suggest the importance of the sap flow sensor placement,
in relation to sinker roots, as to whether lateral roots might be found to exhibit reverse flow during drought. This study
is consistent with the dimorphic rooting habit of Quercus suber trees in which deep roots access groundwater to supply superficial roots and the whole tree, when shallow soil layers were
dry. 相似文献
11.
For the first time, in situ field measurements of sap flow were conducted in adult Dracaena cinnabari plant native to the arid tropical climate of Socotra Island. The heat field deformation (HFD) method was applied using both single and multi-point sensors to study azimuthal and radial sap flow variability in stem, roots and first-order branches over two weeks during a winter monsoon. The main aim of this work was to monitor sap flow in adult D. cinnabari in-situ to better understand its physiological adaptation to extreme arid environments. The second aim was to compare our results with earlier sap flow measurements in adult D. draco uing the same HFD method. The last question we wanted to answer was comparison of sap flow measurements in both, young and adult Dracaena species. We found that sap flow magnitude is low and of a similar range in all observed D. species. High sap flow variability was recorded in different parts of adult D. cinnabari plant which changed throughout the day responding to interplay between intrinsic and extrinsic water potential gradients induced by sunlight. Maximum sap flow levels had variable pattern around stem in response to sun exposure, similarly as it was observed in adult D. draco plant. Sensors installed tangentially in stem xylem showed that water transport in adult D. cinnabari may move in lateral direction. This work also presents several methodological aspects detected from earlier observations of dicots which proved to be more pronounced in adult D. species. These methodologies relate to interpreting negative sap flow rates in conjunction with established axial flow reversal during hydraulic redistribution usually occurring under low evaporative demands and dry soil. Conversely, flow reversal during the day under high evaporative demands and wet soil may designate lateral water movement induced by internal water redistribution. 相似文献
12.
Indications of Hydraulic Lift by Pinus halepensis and Its Effects on the Water Relations of Neighbour Shrubs 总被引:1,自引:0,他引:1
We measured the stable deuterium isotopic composition of xylem sap, the shoot predawn and midday water potentials, and the
leaf δ13C of Mediterranean shrubs Pistacia lentiscus, Globularia alypum and Rosmarinus officinalis in a south-oriented transect from a large (12 m tall) Aleppo pine tree, Pinus halepensis. We aimed to study the possibility of hydraulic lift from the deep roots of this pine tree to the shallow soil layers and
its influence on these neighbour shrubs. These same traits were also studied in several individuals of the shrub Pistacia lentiscus growing with different types of neighbours: just shrubs, a small (3 – 4 m) pine tree, and the above mentioned large pine
tree. The greater the distance from P. halepensis the plants grew, the higher xylem water δD, the lower the soil water content, and, the lower the predawn and midday water
potentials were found. These results suggest the existence of an hydraulic lift from deep roots to shallow soil in this big
tree. Further indication of this existence is provided by the improved water status of P. lentiscus (higher water potentials and δD, and lower δ13C and, therefore, lower water use efficiencies) when growing close to the big pine in comparison with the same shrub species
growing close to small pines or just surrounded by other shrubs. Moreover, all these trends occurred in the dry summer season,
but disappeared in the wet spring season.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Seasonal variation was followed in the content of total a-aminoacids, arginine, calcium, total carbohydrate, ß-galactosidaseactivity, magnesium, nitrate, phosphatase activity, phosphateand sulphate in vacuum-extracted xylem sap from Actinidia chinensisvar. hispida, the Chinese gooseberry or kiwifruit. There wasa marked increase in the concentration of most sap componentsjust prior to leaf emergence followed by a rapid decrease afterthe leaves had expanded. Experiments with excised extensionshoots showed that much of this spring-time increase in concentrationsof sap components was due to mobilization of nutrients withinthe shoot itself. Sap from the trunk and the older brancheschanged less in composition than did sap from the younger partsof the plant. The amplitude and direction of trends in concentrationof sap from the different parts of the plant varied with nutrientand with time. Analysis of vacuum-extracted xylem sap collectedduring periods of rapid transpiration from early summer onwardsgives a reliable indication of the composition of the transpirationstream. Actinidia chinensis, Chinese gooseberry, kiwifruit, storage reserves, xylem sap, amino acids, arginine, calcium, carbohydrate, ßgalactosidase, magnesium, nitrate, phosphatase, phosphate, potassium, sulphate 相似文献
14.
Does Xylem Sap ABA Control the Stomatal Behaviour of Water-Stressed Sycamore (Acer pseudoplatanus L.) Seedlings? 总被引:3,自引:0,他引:3
Sycamore seedlings were grown with their root systems dividedequally between two containers. Water was withheld from onecontainer while the other container was kept well-watered. Effectsof soil drying on stomatal behaviour, shoot water status, andabscisic acid (ABA) concentration in roots, xylem sap and leaveswere evaluated. At 3 d, root ABA in the drying container increased significantly,while the root ABA in the unstressed container of the same plantsdid not differ from that of the control. The increase in rootABA was associated with the increase in xylem sap ABA and withthe decrease in stomatal conductance without any significantperturbation in shoot water status. At 7 d, despite the continuous increase in root ABA concentration,xylem sap ABA showed a marked decline when soil water contentwas depleted below 013 g g1. This reduction in xylemsap ABA coincided with a partial recovery of stomatal conductance.The results indicate that xylem sap ABA is a function of rootABA as well as the flow rate of water from roots to shoots,and that this ABA can be a sensitive indicator to the shootof the effect of soil drying. Key words: Acer pseudoplatanus L., soil drying, stomatal behaviour, xylem sap ABA 相似文献
15.
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
16.
The accumulation, distribution and redistribution of dry matterand nitrogen is described for Helianthus annuus L. cv. Hysun21 grown on 6 mM urea in glasshouse culture. Seed dry matterand nitrogen were transferred to seedlings with net efficienciesof 40 and 86 per cent respectively. At flowering, the stem hadmost of the plant's dry matter and the leaves most of its nitrogen.About 35 per cent of the plant's nitrogen accumulated afterthree-row anthesis. The amount of protein in vegetative parts,especially leaves, declined after flowering. Concentrationsof free amino compounds also decreased during growth. Matureseeds had 38 per cent of the total plant dry weight and 68 percent of the total nitrogen. Seeds acquired 33 per cent of theirdry matter and nitrogen from redistribution from above-groundplant parts. The stem was most important for storage of carbohydrate,leaves the most important for nitrogen. Over 50 per cent ofthe nitrogen in the stem and leaves was redistributed. Plantsthat received 6 mM nitrate accumulated more dry matter thanurea-grown plants. Seeds from nitrate-grown plants were heavier(58 mg) than those of urea-grown plants (46 mg), and their percentageoil was greater (50 and 41 respectively). The amount of nitrogenper seed was the same. Little or no urea was detected in xylem sap of plants suppliedwith 5 mM urea, but it was detected in sap of plants which received25 mM. Concentrations of urea and amino compounds in the sapdecreased up the stem. Plants supplied with nitrate had mostof the nitrogen in xylem sap as NO2, suggesting littlenitrate reduction in roots. Plants grown on 6 mM nitrate andchanged to high levels of urea-nitrogen for 14 days still hadhigh levels of nitrate; little nitrate remained in plants receivinglow levels of urea. When urea is applied in irrigation waterto field-grown sunflower, the nitrogen is subsequently takenup as nitrate due to rapid nitrogen transformations in the soil. Helianthus annuus L., sunflower, urea, nitrate, nitrogen transport, xylem sap, nitrogen accumulation nitrogen distribution 相似文献
17.
MORESHET SAMUEL; COHEN YEHEZKEL; GREEN GEORGE C; FUC MARCEL 《Journal of experimental botany》1990,41(7):833-839
Sap flow (F) and leaf water potential (LWP) were followed diurnallyin mature Valencia and Shamouti orange trees in an orchard.The hydraulic conductance of these trees was computed from thediurnal relationship between the LWP and F. The driving forcefor water movement was estimated from a weighted average ofsunlit and shaded LWP, assuming that leaves in the shade transpireto some extent. LWP of covered, non-transpiring leaves was alsomeasured hourly. It was assumed to represent the xylem waterpotential within the axial conduit of the trunk. Relating coveredLWP to F on an hourly basis enables the computation of the hydraulicconductance of the root system, including axial conductances.The hydraulic conductance of the transpiring crown was computed.Its magnitude was comparable to the root system hydraulic conductance. Key words: Orange trees, hydraulic conductance, sap flow, leaf water potential 相似文献
18.
An application of the methods of irreversible thermodynamicsto the fluxes in plant xylem is examined, and an expressionis derived for the electric current present when a length ofstem is short circuted. After examination of the electrode by-passingefficiency, bioelectricity in Cayratia clematidea (F. Muell.)Domin., maintained under conditions of adequate soil water,is shown to reflect changes in the transpiration rate. Pressuregradients and sap velocities in C. clematidea are estimatedfrom short-circuit current data. It is suggested that the experimentaltechnique described may be useful for continuous measurementsof sap flow or transpiration without disturbing the plant environment. 相似文献
19.
STEINBERG SUSAN L.; MCFARLAND MARSHALL J.; WORTHINGTON JOSIAH W. 《Journal of experimental botany》1990,41(6):653-659
Trunk and branch sap flow were compared with canopy transpirationin a 5-year-old pecan tree (Carya illinoensis Wichita).Total trunk sap flow, measured by a heat balance trunk flowgauge, was 122.8 kg over a 24 h period, corresponding closelyto the 113.4 kg of canopy transpiration measured by a largeprecision weighing lysimeter. Branches, less than half the diameterof the main trunk, had a total sap flow an order of magnitudeless than the total flow in the trunk. Sap flow in a branchwith a northern exposure was 41% less than that with a southernexposure. When sap flow was normalized per unit tree or branchleaf area, peak sap flow in the south branch matched that inthe main trunk. Tree transpiration and the sap flow in trunkand branches began concurrently, indicating little dynamic waterstorage in the trunk above the gauge. The hydraulic conductanceof the entire tree was 8 to 14 x 1014 m s1 Pa1,similar to values found for a number of woody and herbaceousspecies. Key words: Sap flow, Carya illinoensis, transpiration, lysimeter, trunk flow gauge 相似文献
20.
The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.) 总被引:3,自引:0,他引:3
The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 530 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170196 mg ml1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K+ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml1 whereasxylem sap contained much lower levels (0.28 mg ml1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with 14CO2. A concentration gradient ofsugar (2.1 bar m1) was recorded for stems. Levels ofsucrose, amino compounds and K+ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions 相似文献