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1.
A method for measuring xylem hydraulic conductance and embolism in entire root and shoot systems 总被引:12,自引:6,他引:6
Current methods for determining the influence of xylem cavitationon hydraulic conductance are limited to unbranched stem or rootsegments with hydraulic conductances above c. 2 mmol s1MPa1. Lower conductances and/or highly branched systemsare encountered in seedlings, arid-land shrubs, herbs, and distalportions of shoot and root systems of trees. In order to quantifythe hydraulic impact of cavitation in such systems, existingtechniques have been modified. Branched shoot or root systemswere prepared for measurement by removal of leaves, or roottips, respectively. The shoot or root system was enclosed ina vacuum chamber with the proximal end protruding and suppliedwith perfusing solution. Flow through the xylem was inducedby chamber vacuum. Hydraulic conductance was determined fromthe slope of the flow rate versus pressure relationship. Xylemembolism was quantified from the increase in hydraulic conductancefollowing high pressure (100 kPa) perfusion of solution throughthe plant. Examples are provided of the application of the methodto cavitation studies in the cold desert shrub Artemisia tridentata. Key words: Hydraulic conductance, xylem cavitation, embolism, whole root/shoot system 相似文献
2.
Hydraulic and osmotic properties of spruce roots 总被引:9,自引:6,他引:3
Rdinger Marcus; Hallgren Stephen W.; Steudle Ernst; Schulze Ernst-Detlef 《Journal of experimental botany》1994,45(10):1413-1425
Hydraulic and osmotic properties of roots of 2-year-old Norwayspruce seedlings (Plcea abiea (L.) Karst) were investigatedusing different techniques (steady flow, pressure probe, andstop flow technique). Root pressures were measured using theroot pressure probe. Compared to roots of herbaceous plantsor deciduous trees, excised root systems of spruce did not developappreciable root pressure (-0.001 to 0.004 MPa or -10 to 40cm of water column). When hydrostatic pressure gradients wereused to drive water flows across the roots, hydraulic conductivities(Lpr) were determined in two types of experiments: (i) rootpressure relaxations (using the root pressure probe) and (ii)steady flow experiments (pneumatic pressures applied to theroot system or xylem or partial vacuum applied to the xylem).Root Lpr ranged between 0.2 and 8108m s1 MPa1(on average) depending on the conditions. In steady flow experiments,Lpr depended on the pressure applied (or on the flow acrossthe roots) and equalled (0.190.12) to (1.21.7)108m s1 MPa1 at pressures between 0.2 and 0.4 MPaand (1.51.3)108 m s1 MPa1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lpr values were similar. The hydraulicconductivity measured during pressure relaxations (transientwater flows) was similar to that obtained at high pressures(and water flows). Although there was a considerable scatterin the data, there was a tendency of the hydraulic conductivityof the roots to decrease with increasing size of the root system.When osmotic gradients were used to drive water flows, Lpr valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lpr=0.017108 was found for osmotic andLpr=6.4108 m s1 MPa1 in correspondinghydrostatic experiments, i.e. the two values differed by a factorwhich was as large as 380. The same hydraulic conductivity asthat obtained in osmotic experiments using the pressure probewas obtained by the 'stop flow techniquel. In this technique,the suction created by an osmoticum applied to the root wasbalanced by a vacuum applied to the xylem. Lpr values of rootsystems did not change significantly when measured for up to5 d. In osmotic experiments with different solutes (Na2S04,K2S04, Ca(NO3)2, mannitol), no passive uptake of solutes couldbe detected, i.e. the solute permeability was very low whichwas different from earlier findings on roots of herbs. Reflectioncoefficients of spruce roots (O were low for solutes for whichplant cell membranes exhibit values of virtually unity ( 相似文献
3.
A morphologically explicit numerical model for analysing wateruptake by individual roots was developed based on a conductornetwork, with specific conductors representing axial or radialconductivities for discrete root segments. Hydraulic conductivity(Lp; m s1 MPa1) was measured for roots of Agavedeserti Engelm. and Opuntia ficus-indica (L.) Miller by applyinga partial vacuum to the proximal ends of excised roots in solution.Lp was also measured for 40- to 80-mm segments along a root,followed by measurements of axial conductivity and calculationof radial conductivity. Predicted values of Lp for entire rootsbased on two to ten segments per root averaged 1.04±0.07(mean±s.e. mean for n = 3) of the measured Lp for A.deserti and 1.06±0.10 for O. ficus-indica. The modelalso closely predicted the drop in water potential along theroot xylem (xylem); when a tension of 50 kPa was applied tothe proximal ends of 0.2 m-long roots of A. deserti and O. ficus-indica,the measured xylem to midroot averaged 30 kPa compared witha predicted decrease of 36 kPa. Such steep gradients in xylemsuggest that the driving force for water movement from the soilto young distal roots may be relatively small. The model, whichagreed with an analytical solution for a simple hypotheticalsituation, can quantify situations without analytical solutions,such as when root and soil properties vary arbitrarily alonga root. Agave deserti, electrical circuit analog, hydraulic conductivity, Opuntia ficus-indica, water potential 相似文献
4.
Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha1yr1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C3 and C4 agronomic species. The respiration rateof attached main roots was 32 µmol CO2 evolved kg1dry weight s1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C3 and C4 agronomic species.The root hydraulic conductivity had a maximal value of 3 x 107ms1 MPa1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake 相似文献
5.
植物通过木质部管道系统进行水分运输, 木质部的水分运输效率和抗空穴化能力等水力结构特征对于植物物种的分布、抗逆能力等方面起关键性作用。目前, 国内外学者一般采用“冲洗法”进行木质部水力结构研究, 然而在该方法中使用的不同冲洗溶质可能对植物木质部水力结构等产生较大影响, 因此该文研究了3种溶质的冲洗溶液对毛白杨(Populus tomentosa)和油松(Pinus tabulaeformis)枝条的水力导度和抵抗空穴化能力的影响。实验结果表明: 相对于去离子水, 用0.01 mol·L-1的草酸和0.03 mol·L-1KCl溶液作为冲洗溶液, 均导致毛白杨木质部导管和油松管胞的水力导度测定值的增大。KCl导致毛白杨和油松木质部抵抗空穴化能力测定值的提高, 草酸导致杨树抵抗空穴化能力测定值增强, 但导致油松抗空穴化能力显著(p<0.01)减弱。小枝水平上, 毛白杨和油松的水分运输效率和抗空穴化能力之间没有显著相关性。另外, 在截枝实验中发现, 毛白杨小枝木质部水力导度随长度增加变化不大, 而油松枝条的木质部水力导度有逐渐增大的趋势。以上的实验结果表明不同溶质下毛白杨和油松枝条的木质部水力导度和抵抗空穴化能力不同, 草酸和KCl可能对木质部管道系统及纹孔处的果胶等产生作用, 从而使毛白杨和油松的水力结构发生变化。毛白杨与油松水力结构在去离子水、草酸和KCl的作用下的不同结果及两物种截枝试验下水力导度的不同变化趋势表明, 导管运输系统和管胞运输系统可能具有不同的水分运输影响因素。 相似文献
6.
Root Hydraulic Conductivity of Two Cactus Species in Relation to Root Age, Temperature, and Soil Water Status 总被引:6,自引:1,他引:5
The effects of root age, temperature, and soil water statuson root hydraulic conductivity (LP) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, LP at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 107m s1 MPa1 for F. acanthodes and 5.2 ? 107m s1 MPa1 for O.ficus-indica at 11 to 17 weeksof age; LP subsequently declined with increasing root age forboth species. LP was maximal at a temperature of about 10 ?Cfor the youngest roots (13 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), LP increased with temperature from 0?C to 50 ?C, with a Q10 of 1.3 between 20 ?C and 30 ?C. At asoil water potential (soil) of 0.016 MPa, root LP wasindependent of the direction of water flow for both species.Depending on root age, LP declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as soil was reduced from0.016 to 1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow 相似文献
7.
The Effect of Drying Rate on the Survival of Three Desiccation-tolerant Angiosperm Species 总被引:7,自引:1,他引:6
FARRANT JILL M.; COOPER KEREN; KRUGER LYNETTE A.; SHERWIN HEATHER W. 《Annals of botany》1999,84(3):371-379
The effect of drying rate on the survival of three angiospermresurrection plants, Craterostigma wilmsii (homoiochlorophyllous),Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius(homoiochlorophyllous) was examined. All species survived slowdrying, but only C. wilmsii was able to survive rapid drying.C. wilmsii was rapidly able to induce protection mechanismssuch as folding of cell walls to prevent mechanical stress andcurling of leaves to minimize light stress, and thus survivedfast drying. Rapid drying of X. humilis andM. flabellifoliusappeared to allow insufficient time for complete induction ofprotection mechanisms. In X. humilis, there was incomplete replacementof water in vacuoles, the photosynthetic apparatus was not dismantled,plasma membrane disruption occurred and quantum efficiency ofphotosystem II (FV/FM) did not recover on rehydration. Rapidlydried leaves of M. flabellifolius did not fold tightly againstthe stem and FV/FMdid not recover. Ultrastructural studies showedthat subcellular damage incurred during drying was exacerbatedon rehydration. The three species co-occur in environments inwhich they experience high desiccation pressures. C. wilmsiihas few features to retard water loss and thus the ability forrapid induction of subcellular protection is vital to survival.X. humilis and M. flabellifolius are able to retard water lossand protection is acquired relatively slowly. Copyright 1999Annals of Botany Company Chlorophyll fluorescence, Craterostigma wilmsii, drying rate, Myrothamnus flabellifolius, resurrection plant, ultrastructure, Xerophyta humilis. 相似文献
8.
Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm. 总被引:4,自引:0,他引:4
NOBEL PARK S.; SCHULTE PAUL J.; NORTH GRETCHEN B. 《Journal of experimental botany》1990,41(4):409-415
Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, Lp, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q10 of 1.45. Suchvariations in Lp with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, Lp was 2.3 x 107 ms{macron}1MPa{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, Lp for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as Lp for established roots. Hence, the conventionalbelief that rain roots have a higher Lp than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on Lp for rain roots andestablished roots. Lp for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in Lp mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential 相似文献
9.
Mechanisms Controlling Changes in Water Movement Through the Roots of Helianthus annuus L. During Continuous Exposure to Oxygen Deficiency 总被引:2,自引:0,他引:2
The effects of oxygen deficiency on suction-induced water flux(Jv) through detached roots of hydroponically-grown sunflowerwere investigated over a period of up to 6 d. Jv was reducedby the time the oxygen partial pressure in the solution, spargedwith oxygen-free N2, had fallen below 2 kPa (air 20.6kPa). This reduction resulted from a decline in the hydraulicconductivity of the radial pathway for water movement (Lp),although up to 46% of the decline was attributable to changesin the osmotic component of the driving force (). Lp (mm s1MPa1), for aerobic roots was 2.23 ? 105 and foranaerobic roots during the initial 16 h, 1.21 ? 105. At 22 h after the onset of anaerobic treatments, Jv and Lp increased,with Lp values becoming 3 times greater than those measuredbetween 4 h and 16 h of treatment and 1.4 times greater thanin aerated roots. However, Lp increased a further 15-fold whenroots were killed by immersion in boiling water for 2 min. Duringand up to 6 d of anaerobic treatment, some roots retained Lpvalues similar to those at 22 h, while others displayed characteristicstypical of dead roots. At no time was there any indication ofreduced axial conductivity due to xylem vessel blockage. The results are discussed in terms of possible energy sourcesfor the maintenance of root integrity and their importance toplant survival during long periods of severe oxygen shortage. Key words: Anaerobiosis, oxygen deficiency, hydraulic conductivity, osmotic potential, water 相似文献
10.
P.J. Melcher G. Goldstein F.C. Meinzer D.E. Yount T.J. Jones N.M. Holbrook C.X. Huang 《Oecologia》2001,126(2):182-192
Physiological traits related to water transport were studied in Rhizophora mangle (red mangrove) growing in coastal and estuarine sites in Hawaii. The magnitude of xylem pressure potential (Px), the vulnerability of xylem to cavitation, the frequency of embolized vessels in situ, and the capacity of R. mangle to repair embolized vessels were evaluated with conventional and recently developed techniques. The osmotic potential of the interstitial soil water (?sw) surrounding the roots of R. mangle was c. -2.6LJ.52᎒-3 and -0.4Lj.13᎒-3 MPa in the coastal and estuarine sites, respectively. Midday covered (non-transpiring) leaf water potentials (OL) determined with a pressure chamber were 0.6-0.8 MPa more positive than those of exposed, freely-transpiring leaves, and osmotic potential of the xylem sap (?x) ranged from -0.1 to -0.3 MPa. Consequently, estimated midday values of Px (calculated by subtracting ?x from covered OL) were about 1 MPa more positive than OL determined on freely transpiring leaves. The differences in OL between covered and transpiring leaves were linearly related to the transpiration rates. The slope of this relationship was steeper for the coastal site, suggesting that the hydraulic resistance was larger in leaves of coastal R. mangle plants. This was confirmed by both hydraulic conductivity measurements on stem segments and high-pressure flowmeter studies made on excised leafy twigs. Based on two independent criteria, loss of hydraulic conductivity and proportions of gas- and liquid-filled vessels in cryo-scanning electron microscope (cryo-SEM) images, the xylem of R. mangle plants growing at the estuarine site was found to be more vulnerable to cavitation than that of plants growing at the coastal site. However, the cryo-SEM analyses suggested that cavitation occurred more readily in intact plants than in excised branches that were air-dried in the laboratory. Cryo-SEM analyses also revealed that, in both sites, the proportion of gas-filled vessels was 20-30% greater at midday than at dawn or during the late afternoon. Refilling of cavitated vessels thus occurred during the late afternoon when considerable tension was present in neighboring vessels. These results and results from pressure-volume relationships suggest that R. mangle adjusts hydraulic properties of the water-transport system, as well as the leaf osmotic potential, in concert with the environmental growing conditions. 相似文献
11.
Inhibition of Ion Transport in Excised Barley Roots by Abscisic Acid; Relation to Water Permeability of the Roots 总被引:4,自引:0,他引:4
Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (Js) or in permeabilityof the roots to water (Lp). This paper investigates the effectof ABA on Lp and Js separately. It is shown that Lp increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in Js. Inhibitionof Js was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na+, Mg2+, Ca2+, and phosphate as wellas the major ion in the exudate, K+. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport. 相似文献
12.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献
13.
The occurrence of root pressure, the vulnerability of xylemvessels to drought-induced cavitation, and the seasonal changesin hydraulic conductivity due to embolism were studied in theculms of Rhipidocladum racemiflorum (Steud.) McClure, a tropicalvine-like bamboo from central Panama. Positive hydrostatic potentialsup to 120 kPa occurred only during the wet season when the transpirationrate of the plant was low, i.e. at night or during rain events.Although the xylem vessels were large and efficient for conductingwater, they were highly resistant to cavitation. Xylem waterpotentials lower than 4.5 MPa were required to induce50% loss of hydraulic conductivity in culms. The minimum waterpotential reached 3.75 MPa at the end of the 1993 dryseason, so loss of hydraulic conductivity due to embolism remained<10%. The species is adapted to drier habitats both by wayof a low vulnerability to xylem cavitation and by root pressuresin the wet season that could refill vessels that became embolizedduring a severe dry season. Key words: Rhipidocladum racemiflorum, root pressure, cavitation, embolism, water relations 相似文献
14.
Specific conductivity (ks, m2s-1MPa-1) describes the permeability of xylem and is determined by all aspects of xylem anatomy that create resistance to the flow of water. Here we test the hypothesis that ks is a function of radial and vertical position within the stem, rather than solely a function of cambial age (ring number from the pith), by measuring ks on samples excised from 35-year-old Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco] trees at six heights and two or three radial positions. Sapwood ks decreased from the cambium to the heartwood boundary, and the difference between outer and inner sapwood increased with height in the tree. Beneath the live crown, inner sapwood had 80-90% the ks of outer sapwood, but only 55% just 10 m higher in the stem (about 10 nodes down from the tree top). Outer sapwood ks peaked near the base of the crown and declined toward both the base and top of the stem. These patterns can be explained by two superimposed effects: the effect of cambial age on the dimensions of tracheids as they are produced, and the effect of xylem aging, which may include accumulation of emboli and aspiration of bordered pits. Tracheid lumen diameter and earlywood and latewood density and width, all factors known to vary with cambial age, were measured on different trees of the same age and from the same stand. Lumen diameter increased with cambial age, whereas the proportion of latewood and growth ring density increased after an initial decrease in the first 5 years. Our results suggest that the effect of cambial age on xylem anatomy is not sufficient to explain variation in ks. Instead, physical position (both vertical and radial) in the stem and cambial age must be considered as determinants of conductivity. 相似文献
15.
Wolterbeek, H. Th. 1987. Relationships between adsorption, chemicalstate and fluxes of cadmium applied as Cd(NO3)2 in isolatedxylem cell walls of tomato.J. exp. Bot. 38: 419432. Isolated xylem cell wall pieces were applied as membranes inion diffusion experiments. The cell walls were isolated fromtomato internodes (Lycopersicon esculentum Mill, cv. Tiny Tim)and sealed in a two-compartment diffusion system. In flux andadsorption calculations, the cell wall was regarded as a leakymembrane with parallel fluxes through Donnan Free Space (DFS)and Water Free Space (WFS). During the experiments absorptioninto and diffusion across the walls was determined of Cd2 +, applied as 115Cd(NO3)2. Flux experiments with 82Brindicated that excluded volume effects and path tortuosity resultedin apparent WFS diffusion coefficients in the walls which were0·012 times as high as in water. The free proton concentration in the DFS was shown to be relatedto a complex formation between fixed charges and Cd2 +. Thecell wall permeability for Cd2 + and NO3 varied withapplied and absorbed concentrations, and the Cd2 + flux curveshowed an inflexion point coinciding with a buffered degreeof dissociation of fixed charges in the DFS. The necessary couplingof fluxes of opposite charges resulted in relatively high NO3and small Cd2 + permeability of the DFS for strongly dilutedsolutions (P = 104 m s1 and 1011 m s1for NO3 and Cd2 + respectively). The results demonstratethe possible regulatory effects of the cell wall in processesof ion transfer from xylem vessels, or ion uptake in plant tissues. Key words: Cadmium, chemical state, DFS, WFS, ion flux, permeability, xylem cell walls, tomato, bromium, nitrate 相似文献
16.
Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO2assimilation, chlorophyllfluorescence and the chlorophyll content of temperate hostparasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO2assimilation (3.59 ±0.41 µmol m-2 s-1) than I. micranthus(2.42 ± 0.20µmol m-2 s-1), and C. serratus(2.41 ± 0.43 µmolm-2 s-1) showed higher CO2assimilation than T. antarctica(0.67± 0.64 µmol m-2 s-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO2assimilationand electron transport suggests that the lower CO2assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO2assimilation (3.21 ±0.37 µmol m-2 s-1) than mistletoes (2.54 ± 0.41µmol m-2 s-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO2assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (qp), non-photochemical quenching (qn), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand 相似文献
17.
Influence of climate-driven shifts in biomass allocation on water transport and storage in ponderosa pine 总被引:12,自引:0,他引:12
Conifers decrease the amount of biomass apportioned to leaves relative to sapwood in response to increasing atmospheric evaporative demand. We determined how these climate-driven shifts in allocation affect the aboveground water relations of ponderosa pine growing in contrasting arid (desert) and humid (montane) climates. To support higher transpiration rates, a low leaf:sapwood area ratio (AL/AS) in desert versus montane trees could increase leaf-specific hydraulic conductance (KL). Alternatively, a high sapwood volume:leaf area ratio in the desert environment may increase the contribution of stored water to transpiration. Transpiration and hydraulic conductance were determined by measuring sap flow (JS) and shoot water potential during the summer (June-July) and fall (August-September). The daily contribution of stored water to transpiration was determined using the lag between the beginning of transpiration from the crown at sunrise and JS. In the summer, mean maximum JS was 31.80LJ.74 and 24.34Dž.05 g m-2 s-1 for desert and montane trees (a 30.6% difference), respectively. In the fall, JS was 25.33NJ.52 and 16.36dž.64 g m-2 s-1 in desert and montane trees (a 54.8% difference), respectively. JS was significantly higher in desert relative to montane trees during summer and fall (P<0.05). Predawn and midday shoot water potential and sapwood relative water content did not differ between environments. Desert trees had a 129% higher KL than montane trees in the summer (2.41᎒-5 versus 1.05᎒-5 kg m-2 s-1 MPa-1, P<0.001) and a 162% higher KL in the fall (1.97᎒-5 versus 0.75᎒-5 kg m-2 s-1 MPa-1, P<0.001). Canopy conductance decreased with D in all trees at all measurement periods (P<0.05). Maximum gC was 3.91 times higher in desert relative to montane trees averaged over the summer and fall. Water storage capacity accounted for 11 kg (11%) and 10.6 kg (17%) of daily transpiration in the summer and fall, respectively, and did not differ between desert and montane trees. By preventing xylem tensions from reaching levels that cause xylem cavitation, high KL in desert ponderosa pine may facilitate its avoidance. Thus, the primary benefit of low leaf:sapwood allocation in progressively arid environments is to increase KL and not to increase the contribution of stored water to transpiration. 相似文献
18.
Stomatal conductances (gs) of plants of Vicia faba, Raphanussativus, Phaseolus vulgaris, Heilanthus annuus, and Nicotianatabacum were measured in chambers containing either clean airor air containing between 18 and 1000 parts 109 SO2 atwater vapour pressure deficits (vpd) ranging from 1·0to 1·8 kPa. When vpd was low (<1·3 kPa at 22 °C) and stomatawere open, exposure to SO2 induced rapid and irreversible increasesin gs in V. faba. This response persisted throughout the exposure(3 d). The increase in gs, 2030% compared with cleanair, was independent of SO2 concentration up to 350 parts 109Stomatal conductances of polluted plants at night were greaterthan controls. When stomata were closed before exposure to SO2,there was no effect on gs. When vpd was varied, gs of unpolluted plants of P. vulgarisshowed no response, but that of R. sativus increased slightlywith increasing vpd. In both species exposure to SO2 causedan increase in gs at all vpd values. gs of unpolluted plantsof V. faba, H. annuus, and N. tabacum decreased with increasingvpd. At low vpd values exposure to SO2 in these species causedan increase in gs, but, above a certain value of vpd, dependingon species, gs decreased with exposure to SO2. It is postulated that SO2, once in the substomatal cavity, entersthe stomatal complex via adjacent epidermal cells and at lowconcentrations leads to a reduction in turgor in these cellsand consequently to stomatal opening. In vpd-sensitive species,increased transpiration from guard cells or epidermal cellsadjacent to the stomata induced by SO2 may lead to stomatalclosure at large vpd levels. Stomatal sensitivity to vpd insuch cases may be enhanced because adjacent epidermal cell turgoris lowered by SO2. At high SO2 concentrations direct disruptionof guard cell structure may lead to a loss of turgor and stomatalclosure. 相似文献
19.
Tyree Melvin T.; Patio Sandra; Bennink John; Alexander John 《Journal of experimental botany》1995,46(1):83-94
A new high-pressure flowmeter(HPFM)is described which is capableof rapid water-flow measurements. The HPFM permits dynamic determinationof hydraulic conductance of roots, Kr, and can be used in tehlaboratory or field. The base of a root is connected to theHPFM and water is perfused into the root system opposite tothe normal direction of flow during trnaspiration. The perfusionpressure is changed at a constant rate of 37 kPa s1while measuring the flow into the root every 24 s. Theslope of the plot of flow versus applied pressure is Kr. This paper describes the HPFM, presnents the theory of dynamicflow measurements, discusses sources of error, presnets evidencethat dynamic measurements of Kr in Ficus maclellandi (and sixother tropical species from Panama) yield the correct result,and demonstrates the use of the method under field conditionsin Panama on Cecropia obtusifolia and Palicourea guianensis. Key words: High-pressure flowmeter, root and shoot hydraulic conductance, Ficus maclellandi, Cecropia obtusifolia, Palicourea guianensis 相似文献
20.
G. Vercambre C. Doussan L. Pages R. Habib A. Pierret 《Trees - Structure and Function》2002,16(7):479-487
The effect of secondary growth on the distribution of the axial hydraulic conductance within the Prunus root system was investigated. Secondary growth resulted in a large increase in both the number (from about 10 to several thousand) and diameter of xylem vessels (from a few micrometres to nearly 150 µm). For fine roots (<3 mm), an increase in root diameter was correlated with a slight increase in the number of xylem vessels and a large increase in their diameter. Conversely, for woody roots, an increase in root diameter was associated with a dramatic increase in the number of xylem vessels, but little or no change in vessel diameter. The theoretical axial conductivity (Kh, m4.s-1.MPa-1) of root segments was calculated with the Poiseuille-Hagen equation from measurements of vessel diameter. Kh measured using the tension-induced technique varies over several orders of magnitude (7.4᎒-11 to 5.7᎒-7 m4.s-1.MPa-1) and shows large discrepancies with theoretical calculated Kh. We concluded that root diameter is a pertinent and useful parameter to predict the axial conductance of a given root, provided the root type is known. Indeed, the relationship between measured Kh and root diameter varies according to the root type (fine or woody), due to differences in the xylem produced by secondary growth. Finally, we show how the combination of branching pattern and axial conductance may limit water flow through root systems. For Prunus, the main roots do not appear to limit water transfer; the axial conductance of the main axes is at least 10% higher than the sum of the axial conductance of the branches. 相似文献