植物气孔扩散传导率的研究

本文对生长在可控环境温室中的花生气孔扩散传导率进行了实验研究,揭示了单个植株之间、上下表面之间、叶片不同部位以及冠层垂直方向上气孔扩散传导率的变异性。同时以气孔扩散传导率与环境条件的测定值为基础,对传导率对环境因子的反应进行了分析,植株顶部叶片气孔扩散传导率与太阳总辐射和空气饱和差有关系;冠层传导率与冠层截留辐射和空气饱和差有相关关系。     

Does transpiration control stomatal responses to water vapour pressure deficit?

Three types of observations were used to test the hypothesis that the response of stomatal conductance to a change in vapour pressure deficit is controlled by whole-leaf transpiration rate or by feedback from leaf water potential. Varying the leaf water potential of a measured leaf by controlling the transpiration rate of other leaves on the plant did not affect the response of stomatal conductance to vapour pressure deficit in Glycine max. In three species, stomatal sensitivity to vapour pressure deficit was eliminated when measurements were made at near-zero carbon dioxide concentrations, despite the much higher transpiration rates of leaves at low carbon dioxide. In Abutilon theophrasti, increasing vapour pressure deficit sometimes resulted in both decreased stomatal conductance and a lower transpiration rate even though the response of assimilation rate to the calculated substomatal carbon dioxide concentration indicated that there was no ‘patchy’ stomatal closure at high vapour pressure deficit in this case. These results are not consistent with stomatal closure at high vapour pressure deficit caused by increased whole-leaf transpiration rate or by lower leaf water potential. The lack of response of conductance to vapour pressure deficit in carbon dioxide-free air suggests that abscisic acid may mediate the response.     

Is stomatal conductance in a tomato crop controlled by soil or atmosphere?

Summary The effects of soil water deficits and air vapour pressure deficits on stomatal conductance of tomato leaves were analysed separately under field conditions in central Portugal. Three conditions were created: low soil and air humidity (A), high soil and air humidity (B) and low soil but high air humidity (C). The results show that the effect of air vapour pressure deficit on stomatal behaviour is more important than the effect of soil water deficit when the predawn leaf water potential is above –0.4 MPa.     

Stomatal response to vapour pressure deficit and the effect of plant water stress

Abstract The dynamic response of stomata to changes in atmospheric humidity was investigated in Fragaria × ananassa Duch., Picea engelmannii Parry, and Pseudotsuga menziesii (Mirb.) Franco; and the effect of water stress on this response was determined in Pseudotsuga menziesii. The plants were rotated through three regimes of ambient temperature and vapour pressure deficit: 35°C–3. 5kPa, 35°C–0. 5 kPa, and 20°C–1. 5kPa. Branch and leaflet conductance were measured with a steady-state porometer, first at ambient vapour pressure deficit and then at one of four treatment conditions achieved by increasing or decreasing vapour pressure within the porometer cuvette. All three species showed similar stomatal response: enhanced conductance at low vapour pressure deficit and depressed conductance at high vapour pressure deficit. Engelmann spruce was more sensitive than Douglas fir and strawberry. Plant water status significantly altered stomatal response to vapour pressure deficit. The relationship of conductance of xylem water potential was linear under ambient conditions but became curvilinear when conductance was measured above and below ambient vapour pressure deficit. Between ?0. 5 MPa and ?2. 0 MPa xylem water potential, the stomata were sensitive to vapour pressure deficit, but below ? 2. 0 MPa, the sensitivity decreased.     

Water relations of coast redwood planted in the semi-arid climate of southern California

Trees planted in urban landscapes in southern California are often exposed to an unusual combination of high atmospheric evaporative demand and moist soil conditions caused by irrigation. The water relations of species transplanted into these conditions are uncertain. We investigated the water relations of coast redwood (Sequoia sempervirens) planted in the urbanized semi-arid Los Angeles Basin, where it often experiences leaf chlorosis and senescence. We measured the sap flux (J(O)) and hydraulic properties of irrigated trees at three sites in the Los Angeles region. We observed relatively strong stomatal regulation in response to atmospheric vapour pressure deficit (D; J(O) saturated at D < 1 kPa), and a linear response of J(O) to photosynthetically active radiation. Total tree water use by coast redwood was relatively low, with plot-level transpiration rates below 1 mm d(-1) . There was some evidence of xylem cavitation during the summer, which appeared to be reversed in fall and early winter. We conclude that water stress was not a direct factor in causing leaf chlorosis and senescence as has been proposed. Instead, the relatively strong stomatal control that is adaptive in the native habitat of coast redwood may lead to carbon limitation and other stresses in semi-arid, irrigated habitats.     

A model of stomatal conductance to quantify the relationship between leaf transpiration, microclimate and soil water stress

A model of stomatal conductance was developed to relate plant transpiration rate to photosynthetic active radiation (PAR), vapour pressure deficit and soil water potential. Parameters of the model include sensitivity of osmotic potential of guard cells to photosynthetic active radiation, elastic modulus of guard cell structure, soil‐to‐leaf conductance and osmotic potential of guard cells at zero PAR. The model was applied to field observations on three functional types that include 11 species in subtropical southern China. Non‐linear statistical regression was used to obtain parameters of the model. The result indicated that the model was capable of predicting stomatal conductance of all the 11 species and three functional types under wide ranges of environmental conditions. Major conclusions included that coniferous trees and shrubs were more tolerant for and resistant to soil water stress than broad‐leaf trees due to their lower osmotic potential, lignified guard cell walls, and sunken and suspended guard cell structure under subsidiary epidermal cells. Mid‐day depression in transpiration and photosynthesis of pines may be explained by decreased stomatal conductance under a large vapour pressure deficit. Stomatal conductance of pine trees was more strongly affected by vapour pressure deficit than that of other species because of their small soil‐to‐leaf conductance, which is explainable in terms of xylem tracheids in conifer trees. Tracheids transport water by means of small pit‐pairs in their side walls, and are much less efficient than the end‐perforated vessel members in broad‐leaf xylem systems. These conclusions remain hypothetical until direct measurements of these parameters are available.     

Seasonal evolution of diffusional limitations and photosynthetic capacity in olive under drought

This study tests the hypothesis that diffusional limitation of photosynthesis, rather than light, determines the distribution of photosynthetic capacity in olive leaves under drought conditions. The crowns of four olive trees growing in an orchard were divided into two sectors: one sector absorbed most of the radiation early in the morning (MS) while the other absorbed most in the afternoon (AS). When the peak of radiation absorption was higher in MS, air vapour pressure deficit (VPD) was not high enough to provoke stomatal closure. In contrast, peak radiation absorption in AS coincided with the daily peak in VPD. In addition, two soil water treatments were evaluated: irrigated trees (I) and non-irrigated trees (nI). The seasonal evolution of leaf water potential, leaf gas exchange and photosynthetic capacity were measured throughout the tree crowns in spring and summer. Results showed that stomatal conductance was reduced in nI trees in summer as a consequence of soil water stress, which limited their net assimilation rate. Olive leaves displayed isohydric behaviour and no important differences in the diurnal course of leaf water potentials among treatments and sectors were found. Seasonal diffusional limitation of photosynthesis was mainly increased in nI trees, especially as a result of stomatal limitation, although mesophyll conductance (g(m)) was found to decrease in summer in both treatments and sectors. A positive relationship between leaf nitrogen content with both leaf photosynthetic capacity and the daily integrated quantum flux density was found in spring, but not in summer. The relationship between photosynthetic capacity and g(m) was curvilinear. Leaf temperature also affected to g(m) with an optimum temperature at 29 degrees C. AS showed larger biochemical limitation than MS in August in both treatments. All these suggest that both diffusional limitation and the effect of leaf temperature could be involved in the seasonal reduction of photosynthetic capacity of olive leaves. This work highlights the need for models of plant growth and ecosystem function to incorporate new parameters affecting the distribution of photosynthetic capacity in canopies.     

Stomatal responses to changes in temperature at increasing water stress

Summary The response of stomata to a gradual increase in temperature at increasing plant water stress was studied in a hot desert habitat (Negev, Israel) in the field, but under controlled temperature and humidity conditions. Four native species (Zygophyllum dumosum, Artemisia herba-alba, Hammada scoparia, Reaumuria negevensis) and one cultivated plant (Prunus armeniaca) were used in these studies. The stomatal response to temperature was compared with the response in well-irrigated plants of the same species.At low water stress, the diffusion resistance for water vapour decreased in response to a gradual increase in temperature. Transpiration increased accordingly. This response was reversible. All species responded in the same way. The opening of stomata with increasing temperature was apparently independent of the stomatal response regulated by atmospheric humidity. At high plant water stress, the stomatal response was reversed, i.e., the stomata closed when temperature was gradually increased. This stomatal closure was also independent of the closure regulated by atmospheric humidity. The plant water potential at which the stomatal response to temperature was reversed, differed among the species investigated.     

土壤-植物-大气连续体水流阻力分布规律的研究

本文依据田间实测资料,分析了土壤-植物-大气连续体水流阻力的相对重要性,结果表明在连续体中的水流阻力主要分布于从叶气孔腔到大气的扩散过程和根系的吸水过程。叶-气之间的水流阻力比土-根之间要大50倍。最后,讨论了控制连续体水流运动的气孔阻力的变化规律及其与环境因素之间的关系。     

Phenomics allows identification of genomic regions affecting maize stomatal conductance with conditional effects of water deficit and evaporative demand

Stomatal conductance is central for the trades‐off between hydraulics and photosynthesis. We aimed at deciphering its genetic control and that of its responses to evaporative demand and water deficit, a nearly impossible task with gas exchanges measurements. Whole‐plant stomatal conductance was estimated via inversion of the Penman–Monteith equation from data of transpiration and plant architecture collected in a phenotyping platform. We have analysed jointly 4 experiments with contrasting environmental conditions imposed to a panel of 254 maize hybrids. Estimated whole‐plant stomatal conductance closely correlated with gas‐exchange measurements and biomass accumulation rate. Sixteen robust quantitative trait loci (QTLs) were identified by genome wide association studies and co‐located with QTLs of transpiration and biomass. Light, vapour pressure deficit, or soil water potential largely accounted for the differences in allelic effects between experiments, thereby providing strong hypotheses for mechanisms of stomatal control and a way to select relevant candidate genes among the 1–19 genes harboured by QTLs. The combination of allelic effects, as affected by environmental conditions, accounted for the variability of stomatal conductance across a range of hybrids and environmental conditions. This approach may therefore contribute to genetic analysis and prediction of stomatal control in diverse environments.     

Stomatal response functions to environmental stress of dominant species in the tropical Andean páramo

ABSTRACT

Background: Stomatal response functions of dominant plant species can provide insights into the behaviour of ecosystems under environmental stress, and provide tools for modelling their response to climate change. However, they remain little studied in tropical Alpine ecosystems.

Aims: Our objective was to formulate and compare stomatal response functions for two dominant páramo species with different adaptive strategies to drought, the stress-tolerant shrub Hypericum laricifolium, and the stress avoiding giant rosette Espeletia schultzii and thus enable making projections as to their future fitness in a changing climate.

Methods: A reanalysis of data found in the literature and new ecophysiological and micrometeorological measurements were used to fit and test new stomatal response functions to environmental variables for these two species.

Results: The response functions of vapour pressure differences between leaf and air showed an exponential decrease for both species, while for photosynthetically active radiation (PAR), peak-form response functions provided the best fit. The response function for leaf water potential was linear for the drought-tolerant shrub and decreased exponentially for the stress avoiding giant rosette. Several thresholds prior to stomatal closure were also included in the functions.

Conclusions: Although stress-avoiding and stress-tolerant strategies are both successful in the Andean páramo, the response functions suggest that the tolerant shrub could be more resistant to more intense drought.     

Rapid stomatal responses to humidity

The response of leaf conductance in apple to rapid changes in atmospheric humidity was studied using a continuous flow porometer. Leaf-air vapour pressure difference was changed by adjusting the humidity of the inlet air or by altering the flow rate of the air through the chamber. The time course of the response of leaf conductance to leaf-air vapour pressure difference was monitored for periods up to 10 min using a chart-recorder. There were significant changes in leaf conductance within seconds of changing humidity. These were attributed to alterations in stomatal aperture.Abbreviations E evaporation rate - g leaf conductance - PAR photosynthetically active radiation     

Leaf Gas Exchange in Canopy Species of a Venezuelan Cloud Forest

Tropical cloud forests are considered humid ecosystems with frequent cloud cover down to the ground surface. However, seasonal variation in precipitation may induce short-term water stress. For canopy leaves, this water stress may also be a consequence of large atmospheric vapor pressure deficits. The objective of this work was to study five canopy cloud forest species to determine if there are restrictions to leaf gas exchange as a consequence of seasonality in precipitation and to daily water deficit due to air evaporative demand mainly during maximum incoming radiation hours. Seasonal daily courses of microclimatic variables (air temperature, relative humidity, photosynthetic photon flux density) and plant responses (leaf water potential, stomatal conductance, CO₂ assimilation rates, leaf nitrogen concentration) were measured at 2400 m asl in Monterrey, an intermontane valley of the Venezuelan Andes. A gradient in terms of responses to water stress conditions was observed between the species, with Clusia multiflora (a 46% reduction in stomatal conductance between seasons) as the most affected and Miconia resimoides (increased stomatal conductance) responding more favorably to slight water stress conditions. If we consider the limitations of water stress and/or light conditions on CO₂ assimilation we may arrange the species into those in which water stress conditions have a greater impact on leaf carbon gain, those where light conditions are determinant and one in which both water stress and light conditions may affect leaf carbon assimilation.     

北京市5种园林树木蒸腾作用模拟研究

通过对北京市园林5种常用乔木, 国槐(Sophora japonica)、银杏(Ginkgo biloba)、白蜡(Fraxinus chinensis)、杜仲(Eucommia ulmoides)和臭椿( Ailanthus altissima)等植物蒸腾作用与周围环境气象因子(温度、湿度、太阳有效辐射)及植株叶面积指数相关关系的研究, 利用Javis公式计算冠层气孔阻力, 同时采用PM公式计算冠层蒸腾速率和植株日蒸腾量, 并分析不同乔木的冠层气孔导度对环境主要驱动因子的响应规律。结果表明: 5种被观测乔木中, 国槐耗水量最大, 白蜡耗水量最小, 植株蒸腾量大小依次为国槐>银杏>杜仲>臭椿>白蜡(P<0.01)。植物叶片气孔导度及蒸腾量与环境驱动因子太阳辐射及水气压亏缺的相关关系表明, 在土壤水分条件较好时, 国槐长势优于其它4种乔木, 但是其对水分的利用不够经济, 在干旱的情况下不能有效节水。     

Day length regulates seasonal patterns of stomatal conductance in Quercus species

Vapour pressure deficit is a major driver of seasonal changes in transpiration, but photoperiod also modulates leaf responses. Climate warming might enhance transpiration by increasing atmospheric water demand and the length of the growing season, but photoperiod-sensitive species could show dampened responses. Here, we document that day length is a significant driver of the seasonal variation in stomatal conductance. We performed weekly gas exchange measurements across a common garden experiment with 12 oak species from contrasting geographical origins, and we observed that the influence of day length was of similar strength to that of vapour pressure deficit in driving the seasonal pattern. We then examined the generality of our findings by incorporating day-length regulation into well-known stomatal models. For both angiosperm and gymnosperm species, the models improved significantly when adding day-length dependences. Photoperiod control over stomatal conductance could play a large yet underexplored role on the plant and ecosystem water balances.     

Stomatal responses to humidity in isolated epidermes

The ability of guard cells to hydrate and dehydrate from the surrounding air was investigated using isolated epidermes of Tradescantia pallida and Vicia faba . Stomata were found to respond to the water vapour pressure on the outside and inside of the epidermis, but the response was more sensitive to the inside vapour pressure, and occurred in the presence or absence of living, turgid epidermal cells. Experiments using helium–oxygen air showed that guard cells hydrated and dehydrated entirely from water vapour, suggesting that there was no significant transfer of water from the epidermal tissue to the guard cells. The stomatal aperture achieved at any given vapour pressure was shown to be consistent with water potential equilibrium between the guard cells and the air near the bottom of the stomatal pore, and water vapour exchange through the external cuticle appeared to be unimportant for the responses. Although stomatal responses to humidity in isolated epidermes are the result of water potential equilibrium between the guard cells and the air near the bottom of the stomatal pore, stomatal responses to humidity in leaves are unlikely to be the result of a similar equilibrium.     

Soil water deficits decrease the internal conductance to CO2 transfer but atmospheric water deficits do not

The internal conductance to CO₂ supply from substomatal cavitiesto sites of carboxylation poses a large limitation to photosynthesis.It is known that internal conductance is decreased by soil waterdeficits, but it is not known if it is affected by atmosphericwater deficits (i.e. leaf to air vapour pressure deficit, VPD).The aim of this paper was to examine the responses of internalconductance to atmospheric and soil water deficits in seedlingsof the evergreen perennial Eucalyptus regnans F. Muell and theherbaceous plants Solanum lycopersicum (formerly Lycopersiconesculentum) Mill. and Phaseolus vulgaris L. Internal conductancewas estimated with the variable J method from concurrent measurementsof gas exchange and fluorescence. In all three species steady-statestomatal conductance decreased by 30% as VPD increased from1 kPa to 2 kPa. In no species was internal conductance affectedby VPD despite large effects on stomatal conductance. In contrast,soil water deficits decreased stomatal conductance and internalconductance of all three species. Decreases in stomatal andinternal conductance under water deficit were proportional,but this proportionality differed among species, and thus therelationship between stomatal and internal conductance differedamong species. These findings indicate that soil water deficitsaffect internal conductance while atmospheric water deficitsdo not. The reasons for this distinction are unknown but areconsistent with soil and atmospheric water deficits having differingeffects on leaf physiology and/or root–shoot communication. Key words: Carbon dioxide, drought, internal conductance, mesophyll conductance, photosynthesis, stomatal conductance, transfer conductance, vapour pressure deficit, water deficit Received 11 October 2007; Revised 9 November 2007 Accepted 15 November 2007     

冬小麦近轴和远轴叶面气孔对土壤水分胁迫反应的敏感性

当根层土壤水分含量不足,作物体内出现水分胁迫时,小麦叶片两面气孔的反应有明显差异。远轴叶面气孔对水分胁迫的反应比近轴叶面气孔敏感。当出现水分胁迫时,远轴叶面气孔首先收缩,且收缩的程度比近轴叶面气孔大。远轴与近轴叶面气孔阻力的比值(r_(ab)/r_(ab))与根层平均土壤水势(Ψ_s)有关,当Ψ_s大于-50 kPa时,r_(ab)/r_(ad)基本稳定在1.5左右,而当Ψ_s小于-50 kPa时,r_(ab )/r_(ab)随Ψ_s降低而明显增加。     

Analysis of Environmental Effects on Leaf Temperature under Sunlight,High Pressure Sodium and Light Emitting Diodes

The use of LED technology is commonly assumed to result in significantly cooler leaf temperatures than high pressure sodium technology. To evaluate the magnitude of this effect, we measured radiation incident to and absorbed by a leaf under four radiation sources: clear sky sunlight in the field, sunlight in a glass greenhouse, and indoor plants under either high pressure sodium or light emitting diodes. We then applied a common mechanistic energy-balance model to compare leaf to air temperature difference among the radiation sources and environments. At equal photosynthetic photon flux, our results indicate that the effect of plant water status and leaf evaporative cooling is much larger than the effect of radiation source. If plants are not water stressed, leaves in all four radiation sources were typically within 2°C of air temperature. Under clear sky conditions, cool sky temperatures mean that leaves in the field are always cooler than greenhouse or indoor plants-when photosynthetic photon flux, stomatal conductance, wind speed, vapor pressure deficit, and leaf size are equivalent. As water stress increases and cooling via transpiration decreases, leaf temperatures can increase well above air temperature. In a near-worst case scenario of water stress and low wind, our model indicates that leaves would increase 6°, 8°, 10°, and 12°C above air temperature under field, LED, greenhouse, and HPS scenarios, respectively. Because LED fixtures emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures than leaves in greenhouses and under HPS fixtures, but the effect of LED technology on leaf temperature is smaller than is often assumed. Quantifying the thermodynamic outputs of these lamps, and their physiological consequences, will allow both researchers and the horticulture industry to make informed decisions when employing these technologies.     

Stomatal sensitivity to vapour pressure deficit of temperate and tropical evergreen rainforest trees of Australia

Although rainforests of eastern Australia grow in regions of high precipitation, there is a shift from a summer dry season in the temperate south to a winter dry season in the tropical north. Therefore, rainforest trees of eastern Australia provide an opportunity to investigate stomatal sensitivity of mesic trees to vapour pressure deficit (VPD) along a gradient in seasonality of precipitation. Eight rainforest canopy tree species were selected to cover the latitudinal range of rainforests in eastern Australia. Seedlings of these species were grown for a year in glasshouses under ambient conditions or at low VPD and water vapour exchange of leaves was measured during summer. Tropical species, which experience summer-dominant precipitation, showed higher stomatal sensitivities to VPD than temperate species, which experience winter-dominant precipitation. Growing plants under a low VPD increased stomatal sensitivity to increasing VPD in most species. The high stomatal sensitivity to VPD of the tropical species is consistent with the infrequent water stress experienced during their growing season and suggests a high susceptibility to water deficits. In contrast, temperate species may use other mechanisms to maintain photosynthesis under the relatively drier conditions of the temperate growing season.