Diurnal Courses 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.

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.

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~#.

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.

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.