Course Of Stomatal Conductance Research Articles

How does mistletoe infection affect seasonal physiological responses of hosts with different leaf phenology?

Plants should have the ability to perceive physiological changes within their branches when infected by mistletoes, adjusting the use of resources between infected and uninfected branches which can be crucial for their survival in the long-term. Here we investigated how branches infected by the mistletoe Passovia ovata (Pohl ex DC.) Tiegh. and uninfected branches within the same individual tree respond to seasonal environmental changes across two hosts of contrasting leaf phenology (the evergreen Miconia albicans (SW.) Triana and the deciduous Byrsonima verbascifolia (L.) DC.). We measured key leaf traits (instantaneous gas exchange rates, diurnal courses of stomatal conductance, leaf water potential, specific leaf area and leaf macronutrient concentrations) during the peak of the wet and dry season in a seasonal savanna of central Brazil. Pre-dawn leaf water potentials were consistently more negative for infected branches of both hosts, suggesting that overnight water refilling of infected branches was more limited. However, infected and uninfected branches exhibited similar leaf water potentials at midday, suggesting that they undergo similar imbalances in water supply and demand during periods of high atmospheric evaporative demand. Infected and non-infected branches of the evergreen mistletoe showed tighter regulation of water loss, whereas infected branches of the deciduous host were less constrained in regulating leaf transpiration. We also found differences for nutrient concentrations: N, P and K were lower, while Ca was higher in leaves of infected branches. Physiological changes induced by mistletoe infection affected host performance, and were reflected in water and nutrient use differences between infected and uninfected branches. Our findings show that infection responses by mistletoes can be detected between branches within individual trees, and that host species with distinct patterns of leaf phenology are capable to adjust, at the individual level, to cope with mistletoe's imposed physiological stress throughout the year.

Soil moisture regime and palm height influence embolism resistance in oil palm.

With the prospect of climate change and more frequent El Niño-related dry spells, the drought tolerance of oil palm (Elaeis guineensis Jacq.), one of the most important tropical crop species, is of major concern. We studied the influence of soil water availability and palm height on the plasticity of xylem anatomy of oil palm fronds and their embolism resistance at well-drained and seasonally flooded riparian sites in lowland Sumatra, Indonesia. We found overall mean P12 and P50 values, i.e., the xylem pressures at 12% or 50% loss of hydraulic conductance, of -1.05 and-1.86MPa, respectively, indicating a rather vulnerable frond xylem of oil palm. This matches diurnal courses of stomatal conductance, which in combination with the observed low xylem safety evidence a sensitive water loss regulation. While the xylem anatomical traits vessel diameter (Dh), vessel density and potential hydraulic conductivity (Kp) were not different between the sites, palms in the moister riparian plots had on average by 0.4MPa higher P50 values than plants in the well-drained plots. This could largely be attributed to differences in palm height between systems. As a consequence, palms of equal height had 1.3MPa less negative P50 values in the moister riparian plots than in the well-drained plots. While palm height was positively related to P50, Dh and Kp decreased with height. The high plasticity in embolism resistance may be an element of the drought response strategy of oil palm, which, as a monocot, has a relatively deterministic hydraulic architecture. We conclude that oil palm fronds develop a vulnerable water transport system, which may expose the palms to increasing drought stress in a warmer and drier climate. However, the risk of hydraulic failure may be reduced by considerable plasticity in the hydraulic system and the environmental control of embolism resistance, and a presumably large stem capacitance.

Ozone-induced stomatal sluggishness changes stomatal parameters of Jarvis-type model in white birch and deciduous oak.

Stomatal ozone flux is closely related to ozone injury to plants. Jarvis-type multiplicative model has been recommended for estimating stomatal ozone flux in forest trees. Ozone can change stomatal conductance by both stomatal closure and less efficient stomatal control (stomatal sluggishness). However, current Jarvis-type models do not account for these ozone effects on stomatal conductance in forest trees. We examined seasonal course of stomatal conductance in two common deciduous tree species native to northern Japan (white birch: Betula platyphylla var. japonica; deciduous oak: Quercus mongolica var. crispula) grown under free-air ozone exposure. We innovatively considered stomatal sluggishness in the Jarvis-type model using a simple parameter, s, relating to cumulative ozone uptake (defined as POD: phytotoxic ozone dose). We found that ozone decreased stomatal conductance of white birch leaves after full expansion (-28%). However, such a reduction of stomatal conductance by ozone fell in late summer (-10%). At the same time, ozone reduced stomatal sensitivity of white birch to VPD and increased stomatal conductance under low light conditions. In contrast, in deciduous oak, ozone did not clearly change the model parameters. The consideration of both ozone-induced stomatal closure and stomatal sluggishness improved the model performance to estimate stomatal conductance and to explain the dose-response relationship on ozone-induced decline of photosynthesis of white birch. Our results indicate that ozone effects on stomatal conductance (i.e. stomatal closure and stomatal sluggishness) are crucial for modelling studies to determine stomatal response in deciduous trees, especially in species sensitive to ozone.

Effects of ozone-induced stomatal closure on ozone uptake and its changes due to leaf age in sun and shade leaves of Siebold's beech

An estimation of stomatal ozone uptake for the assessment of ozone risks in forest trees can be modified by ozoneinduced stomatal closure. We thus examined a seasonal course of stomatal conductance in sun and shade leaves of Siebold’s beech native to northern Japan (Fagus crenata) grown under free-air ozone exposure. A performance of multiplicative stomatal conductance model was also tested, when considering ozone-induced stomatal closure into the model. Ozone caused stomatal closure in both sun and shade leaves (20% and 30–40% reduction of stomatal conductance in sun and shade leaves, respectively) during early summer. However, in autumn, stomatal closure was diminished regardless of canopy positions (approximately 7% and 6% reduction of stomatal conductance in sun and shade leaves, respectively). When observed seasonal course of stomatal closure was taken into account in stomatal conductance model, the model provided a good agreement with measurements even under conditions of elevated ozone. As a result, ozone-induced stomatal closure limited stomatal ozone uptake by 11% and 17% in sun and shade leaves of Siebold’s beech, respectively. In addition, stomatal ozone uptake in shade leaves under elevated ozone was much less than that in sun leaves (35% of the value in sun leaves), indicating better avoidance of ozone stress in shade leaves. Our results suggest that a loss of ozoneinduced stomatal closure after ozone exposure in the late growing season should be considered in modeling stomatal ozone uptake for the assessment of ozone impacts on Siebold’s beech.

Photosynthetic characterization of three dominant plant species in the saline–alkaline soil of the Yellow River Delta, China

The diurnal variations of photosynthesis of three dominant species, including Glycine soja, Phragmites australis, and Cynanchum chinensis, in the Yellow River Delta in China have been studied under the same natural conditions using a Li-6400 portable photosynthesis system. The results showed that the curves of diurnal variations of net photosynthetic rate (PN) of the three plants were different. The diurnal variation of PN on C. chinensis was a midday depression pattern and had two peaks. However, PN of G. soja and P. australis showed single-peak curves. The transpiration rate (E) of G. soja was significantly higher than that of P. australis and C. chinensis, both showed single-peak curves. In general, the diurnal course of stomatal conductance (gs) followed the same pattern of PN. A similar diurnal pattern of intercellular CO2 concentration (Ci), vapor pressure deficit (VPD), and water use efficiency (WUE) was observed among different species. VPD showed single-peak curves, while WUE was characterized by double-peak curves, which was contrary to Ci. Linear correlations among photosynthetic variables and key environmental factors indicate high positive correlations between PN and E, PN and photosynthetic active radiation, PN and leaf temperature (Tleaf), PN and VPD, and between PN and gs except C. chinensis. Negative correlations among PN and relative humidity, PN and Ci were found. The irradiance response curves derived from the leaves were substantially affected by different species. C. chinensis showed highest apparent quantum efficiency, followed by P. australis and G. soja, while apparent dark respiration (Rd), convexity (k), light saturation point, and maximum gross CO2 assimilation rate (Pmax) of G. soja were higher than those of P. australis and C. chinensis. The irradiance response curve of PN and WUE of different plant species followed the same order: G. soja>C. chinensis>P. australis. They were both higher than most of other species. It was concluded that plant species adapting to the saline–alkaline habitat showed higher photosynthesis. In addition, G. soja is also effective to improve saline–alkaline soil quality.

Performance of a new dynamic model for predicting diurnal time courses of stomatal conductance at the leaf level

Under natural conditions, plants are subjected to continuous changes of irradiance that drive variations of stomatal conductance to water vapour (g(s)). We propose a dynamic model to predict the temporal response of g(s) at the leaf level using an asymmetric sigmoid function with a unique parameter describing time constants for increasing and decreasing g(s). The model parameters were adjusted to observed data using Approximate Bayesian Computation. We tested the model performance for (1) instant changes of irradiance; or (2) continuous and controlled variations of irradiance simulating diurnal time courses. Compared with the two mostly used steady-state models, our dynamic model described daily time courses of g(s) with a higher accuracy. In particular, it was able to describe the hysteresis of g(s) responses to increasing/decreasing irradiance and the resulting rapid variations of intrinsic water-use efficiency. Compared to the mechanistic model of temporal responses of g(s) by Kirschbaum, Gross & Pearcy, for which time constants were estimated with a large variance, our model estimated time constants with a higher precision. It is expected to improve predictions of water loss and water-use efficiency in higher scale models by using a small number of parameters.

Diurnal pattern of stomatal conductance in the large-leaved temperate liana Aristolochia macrophylla depends on spatial position within the leaf lamina.

The large distance between peripheral leaf regions and the petiole in large leaves is expected to cause stronger negative water potentials at the leaf apex and marginal zones compared with more central or basal leaf regions. Leaf zone-specific differences in water supply and/or gas exchange may therefore be anticipated. In this study, an investigation was made to see whether zonal differences in gas exchange regulation can be detected in large leaves. The diurnal course of stomatal conductance, gs, was monitored at defined lamina zones during two consecutive vegetation periods in the liana Aristolochia macrophylla that has large leaves. Local climate and stem water potential were also monitored to include parameters involved in stomatal response. Additionally, leaf zonal vein densities were measured to assess possible trends in local hydraulic supply. It was found that the diurnal pattern of gs depends on the position within a leaf in A. macrophylla. The highest values during the early morning were shown by the apical region, with subsequent decline later in the morning and a further gradual decline towards the evening. The diurnal pattern of gs at the marginal regions was similar to that of the leaf tip but showed a time lag of about 1 h. At the leaf base, the diurnal pattern of gs was similar to that of the margins but with lower maximum gs. At the the leaf centre regions, gs tended to show quite constant moderate values during most of the day. Densities of minor veins were lower at the margin and tip compared with the centre and base. Gas exchange regulation appears to be zone specific in A. macrophylla leaves. It is suggested that the spatial-diurnal pattern of gs expressed by A. macrophylla leaves represents a strategy to prevent leaf zonal water stress and subsequent vein embolism.

Diurnal and seasonal variation in photosynthesis of peach palms grown under subtropical conditions

The Amazonian peach palm (Bactris gasipaes Kunth) has been grown for heart-of-palm production under subtropical conditions. As we did not see any substantial study on its photosynthesis under Amazonian or subtropical conditions, we carried out an investigation on the diurnal and seasonal variations in photosynthesis of peach palms until the first heart-of-palm harvest, considering their relationship with key environmental factors. Spineless peach palms were grown in 80-L plastic pots, under irrigation. Gas exchange and chlorophyll fluorescence emission measurements were taken in late winter, mid spring, mid summer and early autumn, from 7:00 to 18:00 h, with an additional chlorophyll fluorescence measurement at 6:00 h. The highest net CO2 assimilation (P N), observed in mid summer, reached about 15 μmol m−2 s−1, which was about 20% higher than the maximum values found in autumn and spring, and 60% higher than that in winter The same pattern of diurnal course for P N was observed in all seasons, showing higher values from 8:00 to 9:00 h and declining gradually from 11:00 h toward late afternoon. The diurnal course of stomatal conductance (g s) followed the same pattern of P N, with the highest value of 0.6 mol m−2 s−1 being observed in February and the lowest one (0.23 mol m−2 s−1) in September. The maximal quantum yield of photosystem II (Fv/Fm) was above 0.75 in the early morning in all the months. The reversible decrease was observed around midday in September and October, suggesting the occurrence of dynamic photoinhibition. A significant negative correlation between the leaf-air vapour pressure difference (VPDleaf-air) and P N and a positive correlation between P N and g s were observed. The photosynthesis of peach palm was likely modulated mainly by the stomatal control that was quite sensible to atmospheric environmental conditions. Under subtropical conditions, air temperature (T air) and VPDleaf-air impose more significant effects over P N of peach palm than an excessive photosynthetic photon flux density (PPFD). The occurrence of dynamic photoinhibition indicates that under irrigation, peach palms appeared to be acclimated to the full-sunlight conditions under which they have been grown.

A comparison of photosynthethetic characteristics in four poplar clones

The photosynthetic characteristics and the relationship of net photosynthetic rate,water use efficiency with the environmental factors and stomatal conductance in four new poplar clones(3~#、6~#、8~#、9~#) were studied.The results showed that the peak value of the diurnal courses of the photosynthetic rate generally appeared around 10:00,and then reduced gradually.The diurnal courses of transpiration rate in different months were different.The peak value of the diurnal courses of stomatal conductance generally appeared at 7:00~9:00.The total mean net photosynthetic rate(μmol CO_2·m~(-2)·s~(-1)),transpiration rate(mmol H_2O·m~(-2)·s~(-1)) and water use efficiency(mmol CO_2·mol~(-1) H_2O) had following order in June,July and August respectively: Clone 9~#(8.53)6~#(7.21)3~#(6.47)8~#(4.98);Clone 9~#(3.74)3~#(2.76)6~#(1.76)8~#(1.47);Clone 8~#(4.77)6~#(4.35)3~#(2.99)9~#(2.40).Clone 9~# had higher net photosynthetic rate and transpiration rate,with lower water use efficiency.On the contrary,clone 8~# had lower net photosynthetic rate and transpiration rate,with higher water use efficiency.Net photosynthetic rate and water use efficiency had a close relationship with the air temperature and relative humidity in 6~#,and had a close relationship with the photosynthetic active radiation and stomatal conductance in 3~#、8~# and 9~#.

SAP FLOW TRANSPIRATION MEASUREMENTS IN A TABLE GRAPE VINEYARD GROWING IN SOUTHERN ITALY

Optimising crop irrigation management is a general concern in semi-arid climates. Actual crop water use in the field has to be determined as a function of microclimate and of soil water availability. The work described here studies stomatal conductance, transpiration and evapotranspiration of an irrigated vineyard to elucidate their relations with microclimate at decreasing soil moisture availability and to assess their usefulness in determining plant water consumption in the field. The experiment was carried out in a vineyard, trained by the overhead system (“Tendone”), in Southern Italy, in July 1998 for six days in the interval between two irrigations. Stem heat balance gauges were installed on six plants and transpiration flow of one shoot per plant was measured; daily course of stomatal conductance was determined by porometry, and actual evapotranspiration was measured by the Bowen Ratio technique. Results can be summarised as follows: i) at decreasing soil water availability stomatal conductance and transpiration rate decreased and modified their daily pattern, shifting their peaks from noon to mid-morning; ii) sap flow transpiration rates per unit leaf area showed considerable variability among shoots; iii) the daily transpiration course measured by sap flow was in good agreement with actual evapotranspiration measured by the Bowen Ratio method.

Simulations of canopy net photosynthesis and transpiration in Quercus ilex L. under the influence of seasonal drought

A mechanistically based C 3 leaf photosynthesis model combined with an empirical stomatal model and a canopy model of light interception and microclimate was used to simulate Quercus ilex canopy net photosynthesis and transpiration at l'Avic watershed (NE Spain). The model takes into account the sun-shade leaf differentiation of photosynthetic characteristics as affected by depth within the canopy. Based on field studies, simulations were carried out for two locations within the watershed along a gradient in elevation, microclimate and forest structure. Effective predictions of diurnal and seasonal courses of stomatal conductance of sun and shade leaves for different days during the year were obtained by changing a single model variable termed g F. The value of g F determined from least squares of observed vs. simulated time courses was linearly related to pre-dawn xylem water potential over critical ranges of the response curve. Response to g F in the model may to a great extent be thought of as the integrated expression of canopy response to root system generated signals or control mechanisms. For development of predictive capability, g F is extremely useful because it allows seasonal assessments of water use and carbon dioxide uptake with differing patterns in water availability. Based on simulated responses on representative clear, overcast and variable days throughout the year, only small differences in annual totals for net photosynthesis and transpiration were found between the two sites, despite large differences in soil drying. Annual estimates of canopy water loss were in close agreement with independent estimates of evapotranspiration using the hydrological input/output method.

Tissue water relations in elfin cloud forest tree species of Serrania de Macuira, Guajira, Colombia

Diurnal courses of stomatal conductance, leaf water potential, and the components of tissue water potential were measured in six canopy species in an elfin cloud forest. High values of stomatal conductance were measured on cloudy days and during early morning and late afternoon of sunny days. Decreases in stomatal conductance with increases in vapour pressure deficit may have been a response to avoid further water deficits and suggested a stomatal response to changes in relative humidity. Daily transpiration varied between 470 and 1014 g m-2 day-1 during cloudy days and between 532 and 944 g m-2 day-1 during clear days. Stomatal conductance may have also responded to changes in leaf water potential, which was minimum at noon. The minimum tissue water potential measured in the field was -1.8 MPa in Myrcianthes fragrans, and the minimum turgor pressure was 0.49 MPa also in M. fragrans. There was a correlation between the osmotic potential and the minimum tissue water potential, suggesting that osmotic potential plays a major role in the maintenance of turgor in these species, in spite of the great variability in the elastic properties of leaf tissues. Turgor pressure decreased during the day following the course of water potential but never approached the turgor loss point, as it has been measured in some lowland rain forest trees. This is a strong indication that elfin cloud forest trees do not suffer severe water deficits, and that small tree stature is not directly related to water shortage.

Field water relations of a wet-tropical forest tree species, Pentaclethra macroloba (Mimosaceae).

The water relations of Pentaclethra macroloba (Willd.) Kuntze, a dominant, shade-tolerant, tree species in the Atlantic lowlands of Costa Rica, were examined within the forest canopy. Pressure-volume curves and diurnal courses of stomatal conductance and leaf water potential were measured in order to assess differences in water relations between understory, mid-canopy and canopy leaves. Leaves in the canopy had the smallest pinnules but the largest stomatal frequencies and stomatal conductances of the three forest levels. Osmotic potentials at full turgidity decreased with height in the forest; in the canopy and midcanopy they were reduced relative to those in the understory just enough to balance the gravitational component of water potential. Consequently, maximum turgor pressures were similar for leaves from all three canopy levels. Bulk tissue elastic modulus increased with height in the canopy. Leaf water potentials were lowest in the canopy and highest in the understory, even when the gravitational component was added to mid-canopy and canopy values. As a result, minimum turgor pressures were also lowest in the canopy compared to those at lesser heights, and approached zero in full sunlight on clear days.Osmotic potentials at each canopy level were similar for both wet and dry season samples dates suggesting that seasonal osmotic adjustment does not occur. Despite lowered predawn water potentials during the dry season, turgor was maintained in the understory by reduced stomatal conductances.

Stomatal conductance and transpiration of the two faces of Acacia phyllodes

The daily course of stomatal conductance and transpiration was monitored on each separate face of vertical phyllodes of various acacias. The selected phyllodes had a north-south orientation so that one side faced eastwards and the other westwards. The principal measurements were made on Acacia longifolia and A. melanoxylon in Portugal in late summer and autumn, and additional measurements were made on A. ligulata and A. melanoxylon in Australia. In Portugal, irrespective of soil moisture status, conductance showed on early morning maximum with a subsequent gradual decline and sometimes a subsidiary peak in the late afternoon. Maximum conductances appeared to be a function of soil moisture status, whereas the decline in conductance in the late morning and afternoon was correlated with changes in phyllode-to-air vapour pressure deficits rather than changes in phyllode water status. The relationship of transpiration to phyllode water potential did not appear to be influenced by soil moisture status, although transpiration was less in drier soils and in the afternoons, this latter factor contributing to a marked hysteresis in the relationship. The opposing faces of the phyllodes exhibited a high degree of synchrony, showing parallel stomatal opening and closing, despite their large differences in irradiance. Stomatal conductance tended to be higher on the eastern faces in the morning and lower in the afternoon. In A. longifolia the daily average of relative conductance was much the same for both faces, but in A. melanoxylon that of the eastern face was higher and was retained even when the normal orientation of the phyllodes was reversed by turning them through 180°. Synchrony must be achieved by the stomata of both sides responding to common environmental or endogenous signals which are perceived by both surfaces with equal sensitivity.

Optimal water‐use efficiency in a California shrub

Abstract. The stomatal behaviour of a California chaparral shrub was compared with that predicted by a model of optimal water‐use efficiency (Cowan & Farquhar, 1977). The daily courses of stomatal conductance, evaporation, and assimilation were calculated as was the derivative of evaporation with respect to assimilation (∂E/∂A). The derivative ∂E/∂A was not constant, and the measured courses of conductance were not optimal, but daily courses of evaporation and assimilation were usually very close to what would have been predicted had ∂E/∂A been constant. This discrepancy arises because evaporation and assimilation are sometimes so severely constrained by the microenvironment that stomatal conductance has almost no effect on them.

Gas exchange in a 20‐year‐old stand of Scots pine

The rates of net photosynthesis and transpiration of one‐year‐old shoots were measured in situ in five different positions within the crown of a young Scots pine (Pinus sylvestris L.). Measurements were carried out on south‐ and north‐facing shoots on the third and sixth whorls, respectively, and on an east‐facing shoot on the ninth whorl. In another investigation the rates of gas exchange of one‐year‐old shoots on the third whorl of eight different trees were studied. The measurements were made during June and July, 1977, under non‐limiting conditions of soil water. The daily rates of net photosynthesis in whorls three and six followed the light conditions closely, with higher rates for the south side of each whorl and higher for whorl three than six. On whorl nine the shoot had a higher light compensation point and a low rate of photosynthesis at light saturation compared to the other shoot positions. The quantum yield for the shoot on the lowest whorl, as estimated from the linear part of the light response curve, was 50% lower than for shoots on whorl three and six.The variation in transpiration rates was pronounced within the crown as an effect of differences in the absolute value and diurnal course of stomatal conductance. The variation in net photosynthesis was small between different trees while the variation in transpiration was much higher. Thus the variation in water use efficiency was great. It is concluded that it is possible to extrapolate measurements of net photosynthesis from individual trees up to a stand level without introducing large errors in the estimate. More caution must be paid before extrapolating tree transpiration up to stand transpiration. However, before an extrapolation of gas exchange is made from tree to stand level the variation in net photosynthesis and transpiration rate within the crown must be known.

Midday Stomatal Closure in Mediterranean Type Sclerophylls under Simulated Habitat Conditions in an Environmental Chamber: I. Comparison of the Behaviour of Various European Mediterranean Species

Summary Well watered shrubs of ten Mediterranean sclerophyllous species were studied. under simulated habitat conditions in an environmental chamber. Temperature, air humidity and light intensity were altered stepwise to simulate a diurnal course of weather conditions similar to that measured in an evergreen macchia in Portugal on a typical cloudless summer day. Twigs with leaves were enclosed in cuvettes which reproduced the growth chamber climate and which allowed measurement of CO 2 exchange and transpiration. The species investigated differed considerably in stomatal responses at midday to high air temperature and steep leaf to air vapor pressure gradient. Arbutus unedo, Laurus nobilis, Phillyrea angustifolia, Quercus coccifera, Q. ilex, and Q. suber exhibited pronounced midday closure of stomata, which resulted in a strong depression of net photosynthesis and transpiration rates, followed by reopening of stomata and higher rates of CO 2 uptake and water loss. Arbutus andrachne, Nerium oleander, Pistacia lentiscus , and Smilax aspera , on the other hand, showed only a single maximum in stomatal conductance. We conclude, that the differences may reflect species-specific sensitivities of the stomatal apparatus to atmospheric stress in the form of high temperature and low air humidity. All of the species investigated exhibited a lower leaf conductance and a lower net photosynthesis in the afternoon when compared under the same environmental conditions as in the morning. This time dependent response was independent of the absolute degree of maximal conductance and independent of whether or not the diurnal course of stomatal conductance was two-peaked. These observations indicate that it is necessary in the future to consider more carefully the effects of time dependent processes on regulation of stomatal conductance.