Studies on the Movement of Water Through Apple Trees

Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 10¹³ Pa s m^–3 and there was some evidencethat root resistances (R_r) varied with transpiration rate; theratio R_r:R_x (where R_x is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 10^–8 kg kg^–1 Pa^–1). Leaf capacitancevalues ({small tilde}1 x 10^–8 kg Pa^–1 m^–2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s^–1)as values obtained previously.     

The Diffusive Conductivity of the Stomata of Wheat Leaves

A leaf chamber (described in detail) was used alternately witha resistance porometer to measure resistance to viscous flowof air through the leaf, and with a diffusion porometer to measurethe differential diffusive flow of hydrogen and air (V_H–V_A)through the leaf and the component of hydrogen flow (V'_H) movingstraight across the leaf. The resistance of the mesophyll isneeded for interpretation: estimates by three different methodsfor viscous flow did not agree very well, but two differentmethods for diffusive flow gave good agreement. For wheat leaves,only very large errors are important. Formal analysis is in three appendixes: I. Interpretation ofviscous and diffusive flow in small pores involves some problemsin molecular physics, complicated by the particular geometryof the wheat stoma. With some uncertainty, formal expressionsare derived for the viscous resistance of a single stoma, rv,and for the resistances to diffusion of hydrogen and air, andof water vapour and carbon dioxide, all expressed as r_s persquare centimetre of leaf surface. The analysis for hydrogen/airis the most uncertain; that for water vapour and carbon dioxideis more reliable. II. An indication is given of the flow characteristicsof the leaf-chamber system, from which rv can be derived, andof the basis for estimating mesophyll resistance. III. The methodof converting estimates of r_s into estimates of V_H–V_Aand V'_H is given. The results presented are expressed as nearly as possible interms of the quantities which were measured. For five leavesthe dependence of V_H–V_A on V'_H agrees well with theoreticalpredictions; the dependence of V_H–V_A (and V'_H) on rv,on average, agrees well with prediction, but involves the assumptionthat the stomata get shorter as they close. The agreement isgood enough to suggest that the formal expressions for r_s interms of stomatal dimensions and molecular gas constants arereliable enough to be carried forward into future transpirationand assimilation studies. The minimum value of ra for watervapour (c. 3 sec cm⁺¹) is close to values found elsewhere bydifferent techniques. At very small stomatal openings there was a large deviationfrom predicted behaviour, such as would occur if the imposedexcess air pressure further closed the stomata during viscousflow experiments.     

Hydraulic and osmotic properties of spruce roots

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(Lp_r) 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 Lp_r ranged between 0.2 and 810^–8m s^–1 MPa^–1(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)10^–8m s^–1 MPa^–1 at pressures between 0.2 and 0.4 MPaand (1.51.3)10^–8 m s^–1 MPa^–1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lp_r 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, Lp_r valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lp_r=0.01710^–8 was found for osmotic andLp_r=6.410^–8 m s^–1 MPa^–1 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. Lp_r 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 (     

Effects of thinning in a Pinus sylvestris L. stand on foliar water relations of Fagus sylvatica L. seedlings planted within the pinewood

Planting of beech in old Scots pine plantations could facilitate the extension of adjoining small natural populations of beech in the centre of the Iberian Peninsula. To be successful the survival and growth of seedlings after outplanting must be compatible with microclimatic conditions within thinned pine woods. The present paper deals with water relations in beech seedlings following the variation of available radiation and water as a result of thinning. The seedlings were established under an old Scots pine plantation. After pine felling, four situations were generated in terms of radiation. Hemispherical photographs were taken, and global relative irradiance was calculated for every treatment. During two growing seasons predawn water potential (O_pd) was measured and leaf water parameters were derived from P-V curves. The O_pd diminished through the season in all four situations, and the highest values were found when pine density was lowest. Osmotic potential at turgor lost (O?_o) was higher in early summer. A negative relationship was found between osmotic potential at full turgor (O_?full) and symplast solute content on a dry weight basis (N_s). Under the lowest irradiance (unthinned pine trees), O_?full and O_?o were the highest and the bulk modulus of elasticity ()_max) the lowest; )_max decreased in response to the lowest O_pd measured at the end of summer 1998. It was followed by a reduction in the symplastic relative water content and N_s, irrespective of the irradiance. Osmotic adjustment, as a drought tolerance mechanism, was limited under shade conditions (unthinned pine trees), restricting the acclimation of beech seedlings to drought. Therefore, the presence of overstory, necessary for a successful implantation, should not be extended for too many years because of the risk of negative effects on growth and survival, particularly after frequent dry summers.     

Photosynthesis in the Tapinanthus-Diplorhynchus Mistletoe-Host Relationship

Hill reaction activity and gas exchange were studied in thesouthern African mistletoe Tapinanthus vittatus, its host treeDiplorhynchus condylocarpon and uninfected trees of the samespecies. Photosynthetic potential was assessed by measuringHill reaction activities in isolated thylakoids: reaction ratesin the parasite were less than half those of the host or uninfectedtrees. In addition, parasite thylakoids were more sensitiveto heat treatment than those of the trees. Mean maximum CO₂assimilation rates (±s.e.) were significantly lower (4·2±0·24µmol m^-1 s^-1) in the parasite, compared to both uninfectedtrees (7·6±0·22), and those of the infectedhost (5·2±0·27). Chlorophyll contents (±s.e.)were 800±40 mg m^-2 in the parasite, lower in uninfectedtrees (490±80) and lowest in infected trees (310±70).CO₂ assimilation rates calculated on a per unit chlorophyllbasis were similar in parasitized and non-parasitized trees,58±4·3 and 56±2·2 µmol mgchlorophyll^-1 h^-1 respectively, whereas the parasite's maximumCO₂ assimilation rate was considerably lower (20±1·2).Parasite transpiration rates were approximately double thoseof infected trees throughout the daylight period, and somewhathigher than uninfected trees from mid-morning onwards. Overall,parasite were generally less photosynthetically active thanhost plants; additionally, parasite infection was seen to reducehost carbon assimilation rates compared to those of uninfectedtrees.Copyright 1993, 1999 Academic Press Tapinanthus vittatus, Diplorhynchus condylocarpon, mistletoe, photosynthesis, Hill reaction, Zimbabwe     

Field Estimates of Root and Xylem Resistances in Pinus contorta using Root Excision

A root excision technique was used to estimate the proportionof total resistance to water flux residing in the soil, theroot, and the xylem of lodgepole pine (Pinus contorta Douglex. Loud.) trees in the field. Root excision at mid-day alwaysresulted in rapid recovery of leaf water potential when waterwas supplied to the cut stem, suggesting a high soil-root resistance.Transpiration was unaffected if leaf water potential beforecutting was not limiting leaf conductance. By mid-June wateruptake by the excised stem always exceeded calculated crowntranspiration indicating recharge of internal sapwood storage.Predawn leaf water potential before root excision was highlycorrelated with total soil-plant resistance (r² = 0·89)and calculated root water uptake (r² = 0·92).     

Stem radius changes and their relation to stored water in stems of young Norway spruce trees

Changes in the stem radius of young Norway spruce [Picea abies (L.) Karst.] were related to changes in stem water content in order to investigate the relationship between diurnal stem size fluctuations and internally stored water. Experiments were performed on living trees and on cut stem segments. The defoliated stem segments were dried under room conditions and weight (W), volume (V), and xylem water potential (O_s) were continuously monitored for 95 h. Additionally, photos of cross-sections of fresh and air-dried stem segments were taken. For stem segments we found that the change in V was linearly correlated to the change in W as long as O_s was >-2.3ǂ.3 MPa (phase transition point). Stem contraction occurred almost solely in the elastic tissues of the bark (cambium, phloem, and parenchyma), and the stem radius changes were closely coupled to bark water content. For living trees, it is therefore possible to estimate the daily contribution of "bark water" to transpiration from knowledge of the stem size and continuous measurements of the stem radius fluctuations. When O_s reaches the phase-transition point, water is also withdrawn from the inelastic tissue of the stem (xylem), which - in the experiment with stem segments - was indicated by an increasing ratio between (V and (W. We assume that for O_s below the transition point, air is sucked into the tracheids (cavitation) and water is also withdrawn from the xylem. Due to the fact that in living P. abies O_s rarely falls below -2.3ǂ.3 MPa and the xylem size is almost unaffected by radius fluctuations, dendrometers are useful instruments with which to derive the diurnal changes in the bark water contents of Norway spruce trees.     

The Response of the C3-CAM Tree, Clusia rosea, to Light and Water Stress: I. GAS EXCHANGE CHARACTERISTICS

Gas exchange measurements were undertaken on 2-year-old plantsof Clusia rosea. The plants were shown to have the ability toswitch from C₃-photosynthesis to CAM and vice versa regardlessof leaf age and, under some conditions, CO₂ was taken up continuously,throughout the day and night. The light response was saturatedby 120 µmol m^–2 s^–1 typical of a shade plant. Gas exchange patterns in response to light, water and VPD wereexamined. All combinations of daytime and night-time CO₂ uptakewere observed, with rates of CO₂ uptake ranging from 2 to 11µmol m^–2 s^–1 depending upon water status andlight. Categorization of this plant asC₃, CAM or an intermediateis impossible. Differing VPD affected the magnitude of changesfrom CAM to C₃-photosynthesis (0 to 0.5 and 0 to 6.0 µmolm^–2 s^–1 CO₂, respectively) when plants were watered.Under well-watered conditions, but not under water stress, highPPFD elicited changes from CAM to C₃ gas exchange. This is unusualnot only for a shade plant but also for a plant with CAM. Itis of ecological importance for C. rosea, which may spend theearly years of its life as an epiphyte or in the forest understorey,to be able to maximize photosynthesis with minimal water loss. Key words: Clusia rosea, CAM, C₃, stress     

The electromotive force of the Chara membrane during the hyperpolarizing response

The hyperpolarizing response of the Chara internodal cell wasstudied by applying the voltage clamp and constant current techniques.By assuming the membrane as an electromotive force (emf) inseries with a resistance r (which is the sum of a series resistancer_s and the membrane resistance r_m), it was shown that the hyperpolarizingresponse was brought about not only by the increase in membraneresistance but by the increase in membrane emf. The time dependentcurrent-voltage (I–V_m) curve obtained under the voltageclamp during the hyperpolarizing response showed a negativeresistance. The hyperpolarizing response is also an excitation,since it is a transition process of the membrane across a negativeresistance region. (Received July 22, 1974; )     

Carbon Dioxide and Water Vapour Exchange of Leaves on Field-Grown Citrus Trees

Carbon dioxide and water vapour exchange rates were measuredon attached leaves of field-grown citrus trees. The exchangerates were measured continuously during several weeks in thespring of two successive years. These data confirmed the ratherlow rates of maximum CO₂ exchange (6–11 µmol m^–2s^–1) by citrus leaves. However, the maximum rate was maintainedthrough the midday period on only about half the days. On theother days, characterized by high temperatures and high atmosphericwater vapour pressure deficits, pronounced midday depressionsin CO₂ exchange rates were observed. Since midday transpirationremained stable at a constant rate even with increasing vapourpressure deficit, these results indicate that stomatal closurewas occurring. In fact, the data suggest tfiat specific, maximumtranspiration rates were associated with differing rootstocks.Thus, the rate of water supply to the leaves may be an importantfactor in determining the maximum transpiration rate, and therebymediating control of stomatal conductance and the resultantmidday depression in CO² exchange rates.     

The Responses of Net Photosysthesis to Light and Temperature in Spartina townsendii(sensu lato), a C4 Species from a Cool Temperate Climate

Carbon dioxide and water vapour exchanges for single attachedleaves of the temperate C₄ grass Spartina townsendii were measuredunder controlled environment conditions in an open gas-exchangesystem. The responses of net photosynthesis, stomatal resistance,and residual resistance to leaf temperature and photon fluxdensity are described. The light and temperature responses ofnet photosynthesis in S. townsendii are compared to informationon these responses in both temperate C₃ grasses and sub-tropicalC₄ grasses. Adaptation of photosynthesis in this C₄ speciesto a cool temperate climate is indicated both by the light andtemperature responses of net photo-synthesis. Unlike the C₄grasses examined previously, significant rates of net photosynthesiscan be detected at leaf temperatures below 10?C. Rates of netphotosynthesis equal or exceed those reported for temperateC₃ grasses at all of the temperature (5–40?C) and photonflax density (13–2500µmol m^–2 s^–1) conditionsexamined. Maximum rates of net photosynthesis in S. townsendiiare almost double those reported for C₃ herbage grasses. Unliketemperate C₃ grasses, the major limitation to net photosynthesisat low leaf temperatures (10?C and below) is the stomatal resistance,showing that the low residual resistance characteristic of C₄species is maintained in S. townsendii even at low leaf temperatures.     

Physiological and Anatomical Effects of Growth Temperature on Phaseolus vulgaris L. Cultivars

Two Phaseolus vulgaris L. cultivars were grown at 20/15, 25/20,and 30/25 °C day/night temperatures in growth chambers witha 16 h thermoperiod corresponding to the photoperiod. When thefirst trifoliolate leaf was fully expanded rates of CO₂ exchange(CER) were measured at 27 °C and saturating light usinginfrared gas analysis. Stomatal (r_s) and mesophyll resistances,CO₂ compensation points, activities of the enzymes ribulosebisphosphate carboxylase (RuBPCase), glycolate oxidase (GAO),malate dehydrogenase (MDH), and fructose-1, 6 diphosphate (FDP),chlorophyll content, Hill activities, and leaf anatomy at boththe light and electron microscope level were also investigatedin these leaves. Rates of CO₂ exchange in the light, transpiration rate, andchlorophyll content increased with increasing growth temperaturewhile leaf thickness, specific leaf weight, RuBPCase activity,compensation point, and stomatal resistance decreased. Mesophyllresistance also decreased when calculated assuming zero chloroplastCO₂ concentration (rm, o), but not when calculated assuminga chloroplast CO₂ concentration equal to the CO₂ compensationconcentration (rm, g). Average leaf size was maximal in 25/20°C plants while dark respiration, MDH activity, stomataldensity, and starch were minimal. The activities of GAO andFDP and Hill activity were not affected by temperature pretreatment.     

Effect of drought on leaf gland secretion of the mangrove Avicennia germinans L.

This study assessed the effects of salinity changes over space and time upon leaf gland secretion in Avicennia germinans trees growing naturally in an area featuring markedly seasonal rainfall. Soil ? (, soil N MPa) during the wet season was -0.95ǂ.05 and -2.12ǂ.08 at low and high salinity sites, respectively. During the dry season, these values decreased to -3.24ǂ.09 at low salinity and to -5.75ǂ.06 at high salinity. Consequently, predawn and midday plant water potential were lowered during drought at both sites. The rates of secretion (mmol m^-2 h^-1 ) increased during drought from 0.91ǂ.12 during the wet season to 1.93ǂ.12 at low salinity, and from 1.69ǂ.12 during the wet season to 2.81ǂ.15 at high salinity. Conversely, stomatal conductance (g_s) was lowered by both salinity and drought. As xylem osmolality increased during drought, secretion tended to rise exponentially, and g_s decayed hyperbolically. Thus, a trade-off is obtained between enhancement in salt secretion and control of water loss suggested by g_s.     

基于树干液流测定值进行尺度扩展的马占相思林段蒸腾和冠层气孔导度

应用Granier热消散探针,长期监测华南丘陵地马占相思(Acacia mangium)林14棵样树的树干液流(Sap flow),由此计算整树和林段的蒸腾速率,结合同步记录的环境因子,求算冠层平均气孔导度(G_c)。Granier探针的灵敏度较高,能精确测定即使是微弱的液流活动。观测结果显示,树木个体之间的液流密度(J_s)和整树蒸腾(E_t)受树形特征影响较大。马占相思林径级大的树木个体数较少,但占据林段边材总面积和林段蒸腾的比例较大。J_s和E_t的日变化主要受光合有效辐射(Q_o)和空气水蒸气压亏缺(D)的控制,土壤含水量(θ)对较大胸径树木E_t的影响大于胸径较小的树木,个体之间J_s和E_t的差异随θ的下降而缩小。一年中,林段蒸腾(E)在光照和水热条件较好的7月最高,9~12月,由于土壤水分供应的减少致使E值降低,E对D的敏感性下降。G_c与主要环境因子的关系与E相似,如果θ长期偏低,G_c会明显下降,是造成E降低的主要原因。成熟马占相思林在光照充足、水热条件较好的情况下的蒸腾活动旺盛,但对土壤水分胁迫的忍受力较低。     

Water relations of host trees and resistance to the phloem-boring beetle Phoracantha semipunctata F. (Coleoptera: Cerambycidae)

Environmental stresses, particularly water deficit, predispose eucalypt trees to attack by the eucalyptus longhorned borer, Phoracantha semipunctata F. (Coleoptera: Cerambycidae). Our experiments with potted eucalypts revealed that reduced tree water potential was associated with lower resistance to colonization by neonate P. semipunctata, but the linear relationship between water potential and colonization success was reversed at higher larval densities. There was no indication that the bark exudate “kino” served to defend trees from borer attack. Larvae were not able to colonize the cambium of eucalypt logs with high bark moisture, and survival was low under high moisture conditions in artificial hosts composed of pure cellulose. In trees and cut logs with moist bark, larvae failed to reach the cambium, feeding instead in poorer-quality tissues just beneath the bark surface. Our findings suggest that variation in resistance of eucalypts to attack by the borer is associated with moisture content of the bark. Received: 2 September 1998 / Accepted: 8 January 1999     

The Responses of Net Photosynthesis to Vapour Pressure Deficit and CO2 Concentration in Spartina townsendii (sensu lato), a C4 Species from a Cool Temperate Climate

As the initial part of a detailed study of photosynthetic CO₂assimilation in the temperate C₄ grass, Spartina townsendii,the responses of net photosynthesis to the leaf-air vapour pressuredeficit (VPD) and to CO₂ concentration are examined. Water vapourand CO₂ exchange for single attached leaves were measured undercontrolled-environment conditions in an open gas-exchange system.The responses of net photosynthesis, stomatal resistance (r_s),and residual resistance (r_r) to vapour pressure deficit(VPD)and CO₂ concentration under a range of light and temperatureconditions are reported. Net photosynthesis was insensitiveto increase in the VPD up to 1.0 kPa, but beyond this valuenet photosynthesis decreased with further increase in VPD asa result of an increase in r_s. The residual resistance was notaffected by VPD under any of the conditions examined. Net photosynthesisresponded linearly to increase in the CO₂ concentration in theexternal air (C_a up to the normal atmospheric concentrationwhere there was a sharp change in the response, net photosynthesisbeing independent of any further increase in C_a. Differencesbetween the response curves observed here and in other studiesare discussed and the possible reasons for these differencesare considered.     

Water Relations of Chromium VI Treated Bush Bean Plants (Phaseolus vulgaris L. cv. Contender) under both Normal and Water Stress Conditions

The effect of Chromium VI on leaf water potential (^w), solutepotential (^a), turgor potential (^p) and relative water content(RWC) of primary and first trifoliatc leaves of Phaseolus vulgarisL. was studied under normal growth conditions and during anartificially induced water stress period in order to establishthe possible influence of this heavy metal on the water stressresistance of plants. Plants were grown on perlite with nutrientsolution containing 0, 1•0, 2•5, 5•0 or 10•0µg cm^–3 Cr as Na₂Cr₂O₇.2H₂O. The effect of Cr onwater relations was highly concentration dependent, and primaryand first trifoliate leaves were affected differently. The growthreducing concentrations of Cr (2•5, 5•0 and 10•0µg cm^–3) generally decreased _s and _w and increased_p in primary leaves. The 1•0 µg cm^–3 Cr treatmentdid not affect growth, but altered water relations substantially:in primary leaves _w and _p were increased and _s decreased, whilein trifoliate leaves the effect was the opposite. All Cr treatedplants resisted water stress for longer than control plants.The higher water stress resistance may be due to the lower _sand to the increased cell wall elasticity observed in Cr VItreated plants. Key words: Phaseolus vulgaris, Chromium VI, water stress, Richter plot     

Dynamic measurements of roots hydraulic conductance using a high-pressure flowmeter in the laboratory and field

A new high-pressure flowmeter(HPFM)is described which is capableof rapid water-flow measurements. The HPFM permits dynamic determinationof hydraulic conductance of roots, K_r, 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 3–7 kPa s^–1while measuring the flow into the root every 2–4 s. Theslope of the plot of flow versus applied pressure is K_r. This paper describes the HPFM, presnents the theory of dynamicflow measurements, discusses sources of error, presnets evidencethat dynamic measurements of K_r 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     

A reconnaissance approach for hydrology of atoll lagoons

As a reconnaissance tool of the hydrology of atoll lagoons in the micro-tidal environment of the Tuamotu Archipelago, we define and compute "potential" flow rates at lagoon scale under three swell regimes (high, average, and low swell) after assessment of orientation and width of reef-flat spillways using satellite images. As a direct test, the "potential" flows were compared with field measurements of (1) measured inflows across the reef flat (for eight atolls), (2) net outgoing flow through the pass (for three atolls), and (3) lagoon-level variation rates (for four atolls). Absolute values of "potential" and field flows agreed (r²=0.94, n=42, slope ~1). Computed average water renewal times (T_RAV) were also tested against concentrations of dissolved organic matter (DOM). DOM and T_RAV were positively correlated (r²=0.54, n=26; Spearman's r_s=0.54), and this relationship should enable the detection of unusual atolls. This approach would then appear to be useful for the reconnaissance of hydrodynamics processes in comparable micro-tidal environments.     

Crop load affects assimilation rate, stomatal conductance, stem water potential and water relations of field-grown Sauvignon blanc grapevines

The effects of two shoot densities (14 and 44 shoots/vine) andtwo crop levels (one and two clusters/shoot) on gas exchangeand water relations of field-grown Sauvignon blanc (Vitis viniferaL.) were studied in a factorial design over 3 years. The two-clustertreatments had 0.14 MPa higher stem water potential (_stem),1.4 µmol m^–2 s^–1 higher assimilation rate(A), 0.04 mol m^–2 s^–1 higher stomatal conductance(g_s) and 0.008 mol m^–2 s^–1 higher non-stomatal (g_m)conductance. The two-cluster treatments had higher g_s and transpirationrates than the one-cluster treatments, for similar _stem. A quantitativeanalysis suggests that storage capacity cannot account for thesimultaneous increase in g_s and _stem in the two-cluster treatments.Similar g_s-g_m responses were found In the one- and two-clustertreatments, regard less of differences between the treatmentsin g_s-_stem response. Key words: Grapevine, stomatal conductance, assimilation rate, water relations