Stomatal dynamics are regulated by leaf hydraulic traits and guard cell anatomy in nine true mangrove species

Stomatal regulation is critical for mangroves to survive in the hyper-saline intertidal zone where water stress is severe and water availability is highly fluctuant.However,very little is known about the stomatal sensitivity to vapour pressure deficit(VPD)in mangroves,and its co-ordination with stomatal morphology and leaf hydraulic traits.We measured the stomatal response to a step increase in VPD in situ,stomatal anatomy,leaf hydraulic vulnerability and pressure-volume traits in nine true mangrove species of five families and collected the data of genome size.We aimed to answer two questions:(1)Does stomatal morphology influence stomatal dynamics in response to a high VPD in mangroves?with a consideration of possible influence of genome size on stomatal morphology;and(2)do leaf hydraulic traits influence stomatal sensitivity to VPD in mangroves?We found that the stomata of mangrove plants were highly sensitive to a step rise in VPD and the stomatal responses were directly affected by stomatal anatomy and hydraulic traits.Smaller,denser stomata was correlated with faster stomatal closure at high VPD across the species of Rhizophoraceae,and stomata size negatively and vein density positively correlated with genome size.Less negative leaf osmotic pressure at the full turgor(πo)was related to higher operating steady-state stomatal conductance(gs);and a higher leaf capacitance(Cleaf)and more embolism resistant leaf xylem were associated with slower stomatal responses to an increase in VPD.In addition,stomatal responsiveness to VPD was indirectly affected by leaf morphological traits,which were affected by site salinity and consequently leaf water status.Our results demonstrate that mangroves display a unique relationship between genome size,stomatal size and vein packing,and that stomatal responsiveness to VPD is regulated by leaf hydraulic traits and stomatal morphology.Our work provides a quantitative framework to better understand of stomatal regulation in mangroves in an environment with high salinity and dynamic water availability.

MdDGK3-like as a negative regulator participates in ALA-induced PP2AC to promote stomatal opening in apple leaves

5-Aminolevulinic acid(ALA)can inhibit abscisic acid(ABA)-induced stomatal closure.However,the molecular mechanism is unclear.In this study,we found that ALA upregulated the MdPP2AC expression and PP2A activity in the apple(Malus domestica Borkh.cv.‘Fuji’)leaves.With the promoter of MdPP2AC as bait,a diacylglycerol kinase MdDGK3-like was selected by the Yeast One Hybrid(Y1H)from the cDNA library of the epidermis of apple leaves treated by exogenous ALA.Additional to binding the promoter of MdPP2AC,MdDGK3-like was found to inhibit the transcription activity of MdPP2AC promoter,while ALA significantly eliminated the role of MdDGK3-like.In tobacco leaves,MdDGK3-like was localized in the nucleus of stomatal guard cells.Therefore,MdDGK3-like might act as a transcription factor negatively regulating MdPP2AC expression and causing stomatal closure.To further identify MdDGK3-like functions,several transiently transgenic apple leaves(including overexpression and interference)were established.The results revealed that overexpression of MdDGK3-like promoted stomatal closure by increasing Ca^(2+)and H_(2)O_(2)and decreasing flavonol levels in the guard cells.Conversely,MdDGK3-like(i)led the stomatal opening with lower levels of Ca^(2+)and H_(2)O_(2)but higher flavonols.Based on these,we proposed a new hypothesis that ALA up-regulated MdPP2AC expression via negatively regulating the expression of MdDGK3-like to up-regulate PP2A expression and the enzyme activity,which improved the stomatal aperture.Since it was the first time that MdDGK3-like was showed to act as a transcription factor,the proposed model provided a new insight onto the mechanisms of ALA-induced stomatal opening.

Gas flaring cause shifts in mesophyll and stomatal functional traits of Betula pubescens Ehrh.

In petroleum-producing territories of West Siberia(Russia),oil well gas flares have a thermal effect on nearby plant communities.Such communities can be used as models for studying plant acclimation to global warming.In the present study on the effect of the hydrothermal regime at the flare sites on mesophyll and stomatal functional traits of Betula pubescens,leaves were collected from trees at250 m(control site[CS]),200,150 and 100 m(maximum impact site[MIS])from a flare.From the CS to MIS site,the average annual air temperature increased by 0.5℃and bog water level decreased by 17 cm.On plants from the MIS,stomata were 16%smaller and density was 20%lower compared to those at the CS,resulting in lower maximum stomatal conductance in plants from the MIS(mean±SE:MIS 0.84±0.05 mol·m^(-2)s^(-1),CS 1.24±0.06 mol·m^(-2)s^(-1);F=12.6,P<0.01).Mesophyll cell volume was 1.9 times lower at MIS than at CS.Chloroplast numbers per cell also declined with distance from the flares,from 21(MIS)to18(CS;F=15.6,P<0.001),and chloroplast volume was 24%higher at the CS,whereas the number of mesophyll cells and chloroplasts numbers per unit leaf area were 1.9 and 1.8 times higher at the MIS than at the CS,respectively.As a result,leaves from the MIS had a large total mesophyll cell(Ames/A)and chloroplast(Achl/A)surface area per unit leaf area,resulting in a 46%increase in mesophyll conductance in plants from the MIS.Thus,structural changes in leaf epidermis consisted of a decrease in stomatal size and number,could lower transpiration losses with higher temperatures and less water.To compensate for the reduction in leaf conductance due to a decrease in stomatal conductance under these conditions,an increase in the number of mesophyll cells and chloroplasts per unit area provides a greater gas-exchange area and mesophyll conductance.

Hydraulic role in differential stomatal behaviors at two contrasting elevations in three dominant tree species of a mixed coniferous and broad-leaved forest in low subtropical China

Quantifying the variation in stomatal behavior and functional traits of trees with elevation can provide a better understanding of the adaptative strategies to a changing climate. In this study, six water-and carbon-related functional traits were examined for three dominant tree species, Schima superba, Pinus massoniana and Castanopsis chinensis, in a mixed coniferous and broad-leaved forest at two elevations(70 and 360 m above sea level,respectively) in low subtropical China. We hypothesized that trees at higher elevations would develop more efficient strategies of stomatal regulations and greater water transport capacity to cope with more variable hydrothermal conditions than those at lower elevations. Results show that the hydraulic conductivity did not differ between trees at the two elevations, contrary to our expectation. The C. chinensis trees had greater values of leaf mass per unit area(LMA), and the S. superba and C. chinensis trees had greater values of wood density(WD),relative stem water content(RWC), and ratio of sapwood area to leaf area(Hv) at the 360-m elevation than at 70-m elevation. The mean canopy stomatal conductance was greater and more sensitive to vapor deficit pressure at360 m than at 70 m for both S. superba and C. chinensis, while stomatal sensitivity did not differ between the two contrasting elevations for P. massoniana. The midday leaf water potential(ψL) in P. massoniana was significantly more negative at 360 m than at 70 m, but did not vary with increasing elevation in both S. superba and C. chinensis.Variations in Hvcan be related to the differential stomatal behaviors between the two elevations. The variations of stomatal behavior and ψLwith elevation suggested the isohydric strategy for the two broad-leaved species and the anisohydric strategy for the conifer species. The species-specific differences in LMA, WD, RWC, and Hvbetween the two elevations may reflect conservative resource use strategies at the higher elevation. Our findings revealed a close relationship between hydraulic and stomatal behavior and may help better understand the functional responses of forests to changing environmental conditions.

Variations in chlorophyll content, stomatal conductance, and photosynthesis in Setaria EMS mutants

Chlorophyll (Chl) content,especially Chl b content,and stomatal conductance (G_s) are the key factors affecting the net photosynthetic rate (P_n).Setaria italica,a diploid C_4 panicoid species with a simple genome and high transformation efficiency,has been widely accepted as a model in photosynthesis and drought-tolerance research.The current study characterized Chl content,G_s,and P_n of 48 Setaria mutants induced by ethyl methanesulfonate.A total of 24,34,and 35 mutants had significant variations in Chl content,G_s,and P_n,respectively.Correlation analysis showed a positive correlation between increased G_s and increased P_n,and a weak correlation between decreased Chl b content and decreased P_n was also found.Remarkably,two mutants behaved with significantly decreased Chl b content but increased P_n compared to Yugu 1.Seven mutants behaved with significantly decreased G_s but did not decrease P_(n )compared to Yugu 1.The current study thus identified various genetic lines,further exploration of which would be beneficial to elucidate the relationship between Chl content,G_s,and P_n and the mechanism underlying why C_4 species are efficient at photosynthesis and water saving.

GhHSP24.7 mediates mitochondrial protein acetylation to regulate stomatal conductance in response to abiotic stress in cotton

During seed germination,the cotton chaperone protein HSP24.7 regulates the release,from the mitochondrial electron transport chain,of reactive oxygen species(ROS),a stimulative signal regulating germination.The function of HSP24.7 during vegetative stages remains largely unknown.Here we propose that suppression of Gh HSP24.7 in cotton seedlings increases tolerance to heat and drought stress.Elevation of Gh HSP24.7 was found to be positively associated with endogenous levels of ROS.We identified a new client protein of Gh HSP24.7,cotton lysine deacetylase(Gh HDA14),which is involved in mitochondrial protein modification.Elevated levels of Gh HSP24.7 suppressed deacetylase activity in mitochondria,leading to increased acetylation of mitochondrial proteins enriched in the subunit of Ftype ATPase,V-type ATPase,and cytochrome C reductase,ultimately reducing leaf ATP content.Consequently,in combination with altered ROS content,Gh HSP24.7 transgenic lines were unable to coordinate stomatal closure under stress.The regulation circuit composed of Gh HSP24.7 and Gh HDA14 represents a post-translation level mechanism in plant abiotic stress responses that integrates the regulation of ROS and ATP.

Drought stress triggers alterations of adaxial and abaxial stomatal development in basil leaves increasing water-use efficiency

The physiological control of stomatal opening by which plants adjust for water availability has been extensively researched.However,the impact of water availability on stomatal development has not received as much attention,especially for amphistomatic plants.Therefore,the acclimation of stomatal development in basil(Ocimum basilicum L.)leaves was investigated.Our results show that leaves developed under water-deficit conditions possess higher stomatal densities and decreased stomatal length for both the adaxial and abaxial leaf sides.Although the stomatal developmental reaction to water deficit was similar for the two leaf surfaces,it was proven that adaxial stomata are more sensitive to water stress than abaxial stomata,with more closed adaxial stomata under water-deficit conditions.Furthermore,plants with leaves containing smaller stomata at higher densities possessed a higher water use efficiency.Our findings highlight the importance of stomatal development as a tool for long-term acclimation to limit water loss,with minimal reduction in biomass production.This highlights the central role that stomata play in both the short(opening)and long-term(development)reaction of plants to water availability,making them key tools for efficient resource use and anticipation of future environmental changes.

Response of stomatal conductance of two tree species to vapor pressure deficit in three climate zones

Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit （VPD） or relative humidity （RH） has been inadequately understood till now. In this study, responses of stomatal conduc- tance （gs） to VPD in two species of trees （Fraxinus chinensis Roxb., Populus alba L. var. pyramidalis Bge.）in three different climate zones （Jinan with typical warm humid/semi-humid climate, Urumqi with temperate continental arid climate and Turpan with extreme arid desert climate） were measured. Levels of two phytohormones （abscisic acid, ABA; indole-3-acetic acid, IAA） in the leaves of the two tree species at these three sites were also measured by high performance liquid chromatography. The results showed that the responses of gs to an increasing VPD in these two tree species at the three sites had peak curves which could be fitted with a Log Normal Model （gs=a.exp（-O.5（In（DIc）lb）2）. The VPD/RH values corresponding to the maximum g, can be calculated using the fitting models for the two tree species in the three sites. We found that the calculated g, -VPD correlated nega- tively with relative air humidity in the three sites during the plant growth period （April to October 2010）, which showed the values of g,-max-VPD were related to the climate conditions. The prevailing empirical stomatal model （Leuning model） and optimal stomatal behavior model could not properly simulate our measured data. The water use efficiency in the two tree species did not show obvious differences under three very different climatic conditions, but the highest gs, photosynthetic and transpiration rates occurred in P. alba var. of Turpan. The sensitivity in re- sponse of g~ to VPD in leaves of the two trees showed positive correlations with the concentration of ABA, which implied that ABA level could be used as an indicator of the sensitivity of stomatal response to VPD. Our results confirmed that the prediction of the response of gs to VPD might be incomplete in the two current popular models. Therefore, an improved g, model which is able to integrate the results is needed. Also, the stomatal response mechanism of single peak curves of g~ to VPD should be considered.

Improving water-use efficiency by decreasing stomatal conductance and transpiration rate to maintain higher ear photosynthetic rate in drought-resistant wheat

In wheat, the ear is one of the main photosynthetic contributors to grain filling under drought stress conditions. In order to determine the relationship between stomatal characteristics and plant drought resistance, photosynthetic and stomatal characteristics and water use efficiency(WUE) were studied in two wheat cultivars: the drought-resistant cultivar ‘Changhan 58' and the drought-sensitive cultivar ‘Xinong 9871'. Plants of both cultivars were grown in pot conditions under well-watered(WW) and water-stressed(WS) conditions. In both water regimes,‘Changhan 58' showed a significantly higher ear photosynthetic rate with a lower rate of variation and a significantly higher percentage variation of transpiration compared to control plants at the heading stage under WS conditions than did ‘Xinong 9871' plants. Moreover,‘Changhan 58' showed lower stomatal density(SD) and higher stomatal area per unit organ area(A) under both water conditions. Water stress decreased SD, A, and stomatal width(SW), and increased stomatal length in flag leaves(upper and lower surfaces) and ear organs(awn, glume,lemma, and palea), with the changes more pronounced in ear organs than in flag leaves.Instantaneous WUE increased slightly, while integral WUE improved significantly in both cultivars. Integral WUE was higher in ‘Changhan 58', and increased by a greater amount, than in‘Xinong 9871'. These results suggest that drought resistance in ‘Changhan 58' is regulated by stomatal characteristics through a decrease in transpiration rate in order to improve integral WUE and photosynthetic performance, and through sustaining a higher ear photosynthetic rate, therefore enhancing overall drought-resistance.

Quantitative Analysis of Paleoatmospheric CO2 Level Based on Stomatal Characters of Fossil Ginkgo from Jurassic to Cretaceous in China

A better theoretical and practical understanding of the linkage between paleo-CO2 and climate during geological history is important to enhance the sustainable development of modern human society. Development in plant physiology since the 1980s has led to the realization that fossil plants can serve as a proxy for paleoatmosphere and paleobiosphere. As a relict gymnosperm with evolutionary stasis, Ginkgo is well suited for paleoenvironmental reconstruction. This paper analyzes fossil Ginkgo species from integrated strata in the north of China using anatomic data of plant physiology. Using stomatal parameters, a trend for the paleo-CO2 level during the Early-Middle Jurassic and the Early Cretaceous was obtained, which is consistent with the estimates by GEOCARB. The trend is also similar to that of Mean Global Surface Temperature in geological time. Compared with three other atmospheric CO2 concentration parameters, the trend of paleo-CO2 level based on the stomatal parameter of the fossil Ginkgo specimens from three contiguous strata is more exact.

Hydrogen Sulfide May Function Downstream of Nitric Oxide in Ethylene-Induced Stomatal Closure in Vicia faba L.

Pharmacological, laser scanning confocal microscopic （LSCM）, and spectrophotographic approaches were used to study the roles of hydrogen sulfide （H2S） and nitric oxide （NO） in signaling transduction of stomatal movement in response to ethylene in Viciafaba L. Ethylene treatment resulted in the dose-dependent stomatal closure under light, and this effect was blocked by the inhibitors of H2S biosynthesis in V. faba L. Additionally, ethylene induces H2S generation and increases L-/D-cysteine desulfhydrase （pyridoxalphosphate-dependent enzyme） activity in leaves of V. faba L. Inhibitors of H2S biosynthesis have no effect on the ethylene-induced stomatal closure, NO accumulation, and nitrate reductase （NR） activity in guard cells or leaves of II. faba L. Moreover, the ethylene-induced increase of H2S levels and L-/D- cysteine desulfhydrase activity declined when NO generation was inhibited. Therefore, we conclude that H2S and NO probably are involved in the signal transduction pathway of ethylene-induced stomatal closure. H2S may represent a novel component downstream of NO in the ethylene-induced stomatal movement in V. faba L.

Changes in leaf stomatal traits of different aged temperate forest stands

Stomata control carbon and water vapor exchange between the leaves and the atmosphere,thus infl uencing photosynthesis and transpiration.Combinations of forest patches with different stand ages are common in nature,however,information of which stomatal traits vary among these stands and how,remains limited.Here,seven different aged forest stands(6,14,25,36,45,55,and 100 years)were selected in typical temperate,mixed broadleaf-conifer forests of northeast China.Stomatal density,size and relative area of 624 species,including the same species in stands of different ages were selected.Stomatal density,size and relative area were distributed log-normally,differing across all species and plant functional groups.Stomatal density ranged from 4.2 to 1276.7 stomata mm^(–2),stomatal size ranged from 66.6 to 8315.7μm^(2),and stomatal relative area 0.1–93.3%.There was a significant negative relationship between density and size at the species and functional group levels,while the relative stomatal area was positively correlated with density and size.Stomatal traits of dominant species were relatively stable across different stand ages but were significantly different for herbs.The results suggest that stomatal traits remain relatively stable for dominant species in natural forests and therefore,spatial variation in stomatal traits across forest patches does not need to be incorporated in future ecological models.

Study on the Relationship Between the Ploidy Level of Microspore-Derived Plants and the Number of Chloroplast in Stomatal Guard Cells in Brassica oleracea

The relationship between the ploidy level of microspore-derived plants and chloroplast number in stomatal guard cells was studied in cabbage, broccoli, and Chinese kale. In the experiment, distribution statistics analysis and t-test were used to perform statistical analysis on chloroplast number of different ploidy level in those stomatal guard cells mentioned above, and morphology identifying and chromosome counting were used to test accuracy of counting chloroplast number in stomatal guard cells. The chloroplast average number in stomatal guard cells was very similar among the different leaf positions on the same plant and among significantly among the different ploidy the different locations in the same stoma in the same variety. All the leaf, while the chloroplast number varied distributions of the chloroplast number in different ploidy stoma were normal distribution fitted. A correlation has been established between ploidy and chloroplast number in the stomatal guard cells. In every single stoma of microspore-derived plants, the chloroplast number for a haploid should not be more than 10, diploids 11 to 15, and polyploids more than 15. The accuracy of this method for identification of different ploidy plants was 93.93%. Furthermore, the accuracy of this method was reliable and did not vary with the plants growth conditions. Therefore, the chromosome ploidy of plants derived from microspore culture in cabbage, broccoli, and Chinese kale can be identified by simply counting the chloroplast number in stomatal guard cells.

A rapid dehydration leaf assay reveals stomatal response differences in grapevine genotypes

A simple and reliable way of phenotyping plant responses to dehydration was developed.Fully-developed leaves were detached and placed in a closed plastic box containing a salt solution to control the atmospheric water potential in the container.Three hours of dehydration(weight loss of the leaf)was optimal for measuring changes in stomatal response to dehydration.Application of the plant hormone abscisic acid(ABA)prior to leaf detachment decreased the amount of water loss,indicating that the assay was able to detect differences based on a stomatal response to dehydration.Five different Vitis genotypes(V.riparia,V.champinii,V.vinifera cv.Shiraz,V.vinifera cv.Grenache and V.vinifera cv.Cabernet Sauvignon)with known differences in drought tolerance were screened for their dehydration response and the results obtained corresponded to previous reports of stomatal responses in the vineyard.Significant differences in stomatal density along with differences in the amount and rate of water lost indicate differences in dehydration sensitivity among the genotypes screened.Differences in stomatal response to ABA were also detected.Shiraz had the lowest stomatal density and the highest ABA sensitivity among the genotypes screened,yet Shiraz lost the most amount of water,indicating that it was the least sensitive to dehydration.Despite having the highest stomatal density and intermediate stomatal sensitivity to ABA,V.riparia lost the smallest amount of water,indicating that it was the most sensitive to dehydration.The assay presented here represents a simple and reliable phenotyping method for plant responses to leaf dehydration.

Mapping QTLs for stomatal density and size under drought stress in wheat(Triticum aestivum L.)

Stomatal density and size affect plant water use efficiency, photosynthsis rate and yield. The objective of this study was to gain insights into the variation and genetic basis of stomatal density and size during grain filling under drought stress（DS） and well-watered（WW） conditions. The doubled haploid population derived from a cross of wheat cultivars Hanxuan 10（H10）, a female parent, and Lumai 14（L14）, a male parent, was used for phenotyping at the heading, flowering, and mid- and late grain filling stages along with established amplified fragment length polymorphism（AFLP） and simple sequence repeat（SSR） markers. The stomatal density of doubled haploid（DH） lines was gradually increased, while the stomatal lengths and widths were gradually decreased during grain filling stage. Twenty additive QTLs and 19 pairs of epistatic QTLs for the 3 traits were identified under DS. The other 20 QTLs and 25 pairs epistatic QTLs were obtained under WW. Most QTLs made more than 10% contributions to the total phenotypic variations at one growth stage under DS or WW. Furthermore, QTLs for stomatal density near Xwmc74 and Xgwm291 located on chromosome 5A were tightly linked to previously reported QTLs regulating total number of spikelets per spike, number of sterile spikelets per spike and proportion of fertile spikelets per spike. Qsw-2D-1 was detected across stages, and was in the same marker region as a major QTL for plant height, QPH.cgb-2D.1. These indicate that these QTLs on chromosomes 5A and 2D are involved in regulating these agronomic traits and are valuable for molecular breeding.

CO_2, H_2O exchange and stomatal regulation of regenerated Camptotheca acuminata plantlets during ex vitro acclimatization

For finding the changes in CO2, H20 exchange and their stomatal regulation during ex vitro acclimatization of regenerated Camptotheca acuminata plantlets, the net photosynthesis rate （Pn）, respiration rate （Ro）, light compensation point （Lc） and light saturation point （Ls）, transpiration rate （Tr）, stomatal conductance （gs） and water use efficiency（WUE） were measured during 37 days of ex vitro acclimatization. The results showed that Pn sharply increased until 29 days, then slightly decreased. A substantial decrease in Lc and a substantial increase of Ls in the former two weeks were observed, indicating the light regime enlargement for effective leaf photosynthesis. Tr and gs abruptly decreased during the first week then linearly increased until 29days ex vitro acclimatization, reflecting the strong regulation effect of stomata on water changes of ex vitro acclimating plantlets. Stomatal regulation effect on CO2 exchange was different from that on water exchange, i.e. P, was almost independent of gs during the first week, while P. was significantly correlated with gs thereafter （i.e. dual patterns）. Different from dual patterns of gs-Pn relation, the Tr monotonously linearly increased with gs. Furthermore, WUE was almost independent on gs during the first week, while a marked decreasing tendency with gs was found thereafter. At the beginning of the acclimatization, WUE was mainly determined by photosynthetic capacity, while transpiration becomes a main determinant factor for WUE from 7 to 37 days＇ acclimatization.

Responses of leaf stomatal and mesophyll conductance to abiotic stress factors

Plant photosynthesis assimilates CO_(2)from the atmosphere,and CO_(2)diffusion efficiency is mainly constrained by stomatal and mesophyll resistance.The stomatal and mesophyll conductance of plants are sensitive to abiotic stress factors,which affect the CO_(2)concentrations at carboxylation sites to control photosynthetic rates.Early studies conducted relevant reviews on the responses of stomatal conductance to the environment and the limitations of mesophyll conductance by internal structure and biochemical factors.However,reviews on the abiotic stress factors that systematically regulate plant CO_(2)diffusion are rare.Therefore,in this review,the rapid and long-term responses of stomatal and mesophyll conductance to abiotic stress factors(such as light intensity,drought,CO_(2)concentration and temperature)and their physiological mechanisms are summarized.Finally,future research trends are also investigated.

Leaf Morphological and Stomatal Variations in Paper Birch Populations along Environmental Gradients in Canada

Variations in leaf morphology and stomatal characteristics have been extensively studied at both inter- and intraspecific levels although not explicitly in the context of paper birch (Betula papyrifera Marsh) populations. The birch populations might have developed the leaf variations that allowed them to adapt to a wide climatic gradient. Therefore, in this study we examined variations in the leaf morphological and stomatal characteristics of sixteen paper birch populations collected across Canada and grown in a common garden. We also examined the relationship between these leaf characteristics and the climate of the population’s origin. Significant genotypic differences were found in the leaf characteristics measured among the birch populations. Thus, we expected that the observed leaf variations may be partly explained as natural diversity in the birch due to differences in environment of origin. We noticed that along mean annual precipitation and aridity gradients, hair density on leaf adaxial surface had decreased whereas stomatal density increased significantly. Our results showed that the populations with larger leaf area and specific leaf area had higher hair density but low stomatal density. These leaf characteristics provided a structural basis in reducing water loss through leaves and increasing water use efficiency. A trade-off between stomatal area and density resulted in this study might be a strategy of the birch to balance stomatal conductance in decreased precipitation.

Study on Transpiration and Stomatal Conductance Characteristics of C3 and C4 Plant

The transpiration experiment was done under greenhouse conditions with a C3 plant sweet pepper （Capsicum annuum Linn.） and two C4 plants, sorghum （Sorghum bicolor L.Moench） and maize （Zea mays Linn.）. Three species were irrigated with three different water treatment levels of 100%, 66% and 33% which gave a comparison of tolerance and adaptation to irrigation and two different levels of water stress. The measurements of transpiration rate and stomatal conductance were done between 8.00 a.m. and 16.00 p.m. with measurements about each 1.5 h with an infrared gas analyzer. The results showed that Z. mays probably due to a higher leaf area had very low values and was significantly different （LSD pairwise comparison） from C. annuum and S. bicolor. The hypotheses that C4 plants and C3 plants have different transpiration rates and stomatal conductance could not be shown with the results. However, the hypotheses that for the same species, the highest values in transpiration rate and stomatal conductance were with the 100% irrigation treatment and the lowest values were with the 33% irrigation treatment could be accepted due to the results of this trial.