Stomata in Anthurium (Araceae)

Fig 1. Paradermic sections displaying stomata on the abaxial surface of Anthurium andraeanum cv. Rubi leaves grown in vitro in culture medium containing various concentrations of sodium silicate. a) Control, b) 0.5 mg L-1 , c) 1.0 mg L-1 , d) 2.0 mg L-1

 

Photosynthesis and leaf anatomy of Anthurium cv. Rubi plantlets cultured in vitro under different silicon (Si) concentrations

by Gomes Dias G. M., Rodrigues Soares J. D., Pasqual M., Lara Silva R. A., de Almeida Rodrigues L. C., Pereira F. J., de Castro E. M. (2014)

Gabrielen de Maria Gomes Dias1* , Joyce Dória Rodrigues Soares1 , Moacir Pasqual1 , Renata Alves Lara Silva1 , Luiz Carlos de Almeida Rodrigues2 , Fabricio José Pereira2Evaristo Mauro de Castro2

1 Federal University of Lavras (UFLA), Departamento of Agriculture, Plant Tissue Culture Laboratory, Postal Office 3037, 37200-000, Lavras- MG, Brazil

2 Federal University of Lavras (UFLA), Departamento of Biology, Postal Office 3037, 37200-000, Lavras- MG, Brazil

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in Austral. J. Crop Science AJCS 8(8): 1160-1167 – ISSN:1835-2707 –

https://pdfs.semanticscholar.org/8a93/4a54f0acbe7f9c8e0dc43496a05d41d552ed.pdf

Abstract

The silicon can induce beneficial changes in plants, such as the further development of tissues and increased photosynthetic rate. Thus, studies on the anatomical changes resulting from in vitro culture are key to better understanding the development of micropropagated plants.

Therefore, this study was undertaken to evaluate the morphological and physiological differences in plants with the use of silicon added to the medium for the in vitro culture of Anthurium adreaenum cv. Rubi.

Nodal segments of seedlings were established in vitro and inoculated in Pierik medium supplemented with 30 g L-1 sucrose and solidified with 1.8 g L- 1 PhytagelTM. Different concentrations of sodium silicate (Na2SiO3 ) (0.0, 0.5, 1.0 and 2.0 mg L-1 ) were added to the medium. The experimental design was completely randomized with 30 repetitions. The segments were maintained for 100 days in a growth chamber under controlled conditions and evaluated anatomically and scanning electron microscopy (ultrastructurally) and for their photosynthetic capacities.

Medium containing 1.0 mg L-1 sodium silicate promoted the development of higher stomatal densities on the sheets. For the polar (31.38 µm) and equatorial (31.33 µm) diameter of the stomata of the abaxial leaf, the highest averages occurred in the treatment with 2.0 mg L-1 . Greater relative polar and equatorial diameters were estimated with a peak concentration of 1.2 mg L-1 . The increase in the sodium silicate concentration led to thinning of the abaxial and adaxial epidermis.

The thickness of the central rib had a sharp decrease up to 1.3 mg L-1 . For the mesophyll, the control displayed a higher thickness, whereas the addition of sodium silicate to the culture medium promoted a decrease. Seedlings grown in sodium silicate displayed significant differences, with increased photosynthetic and transpiration rates, stomatal conductance and internal CO2 concentrations. As for the ratio between the internal and external concentrations of CO2 , no significant differences were observed. The addition of sodium silicate resulted in increased epicuticular wax deposition and the formation of structures reserved for depositing calcium. Therefore, under in vitro conditions, the addition of sodium silicate to the culture medium affected the photosynthesis and leaf anatomy of A. andraeanum cv. Rubi, developing anatomical and physiological characteristics that contributed to the survival ex vitro.

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The leaves have stomata flanked on each side by two subsidiary cells parallel to larger stomatal axis (Fig 1A and B). Stomata showing two subsidiary cells displayed parallel to the larger stomatal axis are often classified as type brachyparacytic type (Castro et al., 2009). So, A. andraeanum stomata may be classified as paracytic type. Stomatal types in Araceae are very diverse and some species may show anomocytic, actinocytic, paracytic, and cyclocytic stomata (Wang and Zhao, 2002). Therefore, the brachypracytic stomata described by A. andraeanum may be an important characteristic for correct identification and was also reported by Mantovani et al. (2010) for some Anthurium species. Stomata guard cells showed a large number of chloroplasts and the usual bean-like shape (Fig. 1A). Despite the chloroplasts in stomatal guard cells is a very common anatomical characteristic (Castro et al., 2009) it was not highlighted by previous works in Anthurium anatomy (Wang and Zhao, 2002; Mantovani et al., 2010). Anticlinal cell walls are deeply sinuous in epidermal cells (Fig. 1A-D). Araceae leaves may show straight to very sinuous anticlinal cell walls in epidermal cells but a given species often show just one type (Keating, 2003). In nine Brazilian Anthurium species, Matovani et al. (2010) described from straight to undulated anticlinal cell walls. Therefore, the very sinuous anticlinal cell walls from A. andraeanum may be an important anatomical trait. The stomata are distributed only on the abaxial surface of leaves, classifying the se organs as hypostomatous (Fig 1). Hypostomatous leaves were also described in another Anthurium species by Mantovani et al. (2010) and Saito and Lima (2009).

Stomata in Philodendron Schott (Araceae)

 

 

Comparative leaf morphology and anatomy of some neotropical Philodendron Schott (Araceae) species

by Klimko M., Wawrzynska M., Wiland-Szymanska J. (2014)

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in Steciana 18(3): 159-171 – DOI 10.12657/steciana.018.016

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.agro-a6431801-a508-411b-898d-622f2b09fc4b

Abstract

A comparative morphological and anatomical study on the petioles and lamina of 22 taxa (species, subspecies and cultivars) of the genus Philodendron (subgenera Meconostigma, Pteromischum and Philodendron) has been made in order to investigate interspecific differences which may be useful in species identification.

All species have bifacial leaves with petioles, amphistomatic with a strongly reduced density of stomata on the adaxial leaf surface. The species differ in the size and shape of their epidermal cells, the distribution and types of stomata and cuticle ornamentation in the lamina, thickness of epicuticular layer, presence or absence of hypodermis, structure of spongy mesophyll, thickness of palisade and spongy mesophyll layers, as well as types of raphides, and in the structure and forms of petioles.

A combination of these characters may be useful in species identification. This study shows that there is some variation in petiole and leaf morphological and anatomical characters among the 22 taxa of Philodendron. However, many characters are present in all of them and may be typical of the genus.

The study revealed several detailed interesting epidermal and anatomical features that have not previously been reported in the genus.

Stomata in Crabbea (Acanthaceae)

 

 

Systematics of Crabbea Harv. (Acanthaceae) in southern Africa

Mendes de Gouveia N. A. (2017)

Nelson Alexander Mendes de Gouveia,

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in Thesis MAGISTER SCIENTIAE In the Faculty of Natural and Agricultural Sciences Department of Plant Sciences (Botany) University of the Free State –

http://scholar.ufs.ac.za:8080/xmlui/bitstream/handle/11660/6459/DeGouveiaNAM.pdf?sequence=1

SUMMARY

The purpose of this study is to provide an updated taxonomic revision and a molecular phylogenetic investigation of Crabbea Harv. (Acanthaceae) in southern Africa. The taxonomic component of this study entailed a detailed analysis of anatomical, macromorphological and micromorphological data and appropriate descriptions.

Updated distribution maps of each southern African Crabbea species is presented and detailed habitat and ecological information is also provided. Four different identification keys were constructed using leaf anatomy, leaf micromorphology, pollen micromorphology and macromorphology. Type literature, type material and nomenclature for each investigated Crabbea species is critically reviewed. In cases where holotype material could not be located and/or identified, appropriate isotypes, lectotypes, syntypes and/or neotypes were assigned and/or confirmed. Additional herbarium specimens, on loan and electronic scans, from various European and South African herbaria were studied to construct identification keys, species descriptions, distribution maps and obtain ecological and habitat information.

Fresh material was collected for each investigated species. The investigated Crabbea species are all small to medium-sized herbs with cymose inflorescences and corolla being two-lipped, zygomorphic, funnel-shaped with paired, raised bosses. The corolla tube is largely creamish-white but light pink corolla tubes are occasionally found. Growth form, root appearance, stem orientation, position, texture and leaf shape and indumentum are important for species-level identification.

Leaf micromorphological characters are both significant on species level. The occurrence of both amphistomatic and hypostomatic leaves among the investigated species are characteristic of Acanthaceae and could be effectively used to distinguish the investigated Crabbea species from each other. This study provides a first detailed analysis of Crabbea cystoliths. Cystolith attachment width on the adaxial leaf surface proves to be the best character state to split the southern African Crabbea into two groups. The groupings obtained were similar to that of the leaf micromorphology groupings. xxiii Pollen micromorphology divided Crabbea into two groups based on the absence or presence of murus and lumin. However, this character set yielded a different grouping from the leaf micromorphology and anatomy character sets. Pollen grain morphology for certain Crabbea species either remained constant over a geographic range, or varied between and within populations. Macromorphology could key-out all species, except C. cirsioides and C. nana. This character set displays a similar grouping to that of the pollen micromorphology character set. The molecular phylogenetic component of this study resulted in the first molecular investigation of the phylogeny for the southern African Crabbea species. The phylogeny is primarily based on the two chloroplast DNA sequences trnL-trnF and rps16; however, anatomical and morphological characters are also included in the phylogeny to increase the resolution of the tree in absence of the ITS sequences. Molecular phylogenetic results suggest that C. velutina is the first diverging southern African Crabbea species, from the larger Crabbea clade, consisting of C. acaulis, C. angustifolia, C. cirsioides, C. galpinii, C. ovalifolia and C. pedunculata. Within the larger Crabbea clade, C. acaulis forms a distinct clade as well as C. galpinii and C. pedunculata. The molecular results confirm the close relationship between C. galpinii and C. pedunculata. Moreover, within the larger Crabbea clade, molecular data could not clearly resolve and group the sprawling Crabbea species into distinct clades, as in the case of C. angustifolia, C. cirsioides and C. ovalifolia. The end result of this systematic study provides a new insight into the classification of the southern African Crabbea species and the genus Crabbea. Crabbea galpinii and C. pedunculata are confirmed as two separate, sister species and C. nana is now regarded as a synonym of C. cirsioides. Seven Crabbea species are recognised in southern Africa.

Stomata in Acanthaceae

Investigations on foliar epidermal characteristics in some Acanthaceae

by Patil A. M., Patil D. A. (2011)

Patil, A. M.1* and D. A. Patil2

1Department of Botany, Rani Laxmibai College, Parola-425111, District Jalgaon, Maharashtra, India
2P.G. Department of Botany, S.S.V.P.S’s L.K.Dr.P.R.Ghogrey Science College, Dhule – 424005, Maharashtra, India

 

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in Current Botany 2(9): 01-08 – ISSN: 2220-4822 –

1376-Article Text-1639-1-10-20151031.pdf

Abstract

The paper communicates observations on foliar epidermal characteristics of hitherto uninvestigated 22 species belonging 17 genera of the family Acanthaceae.

Except few other types, diacytic type of stomata in generally noticed. The other types are rarely to occasionally on the same foliar surface. The other foliar features such as stomatal index and frequency, types of subsidiaries, stomatal abnormalities, cell inclusions, cell wall contours, etc. are described in detail.

Their taxonomic significance is discussed pertinently.

Stomatal densities drive the partitioning of conductance between leaf sides

 

 

Pore size regulates operating stomatal conductance, while stomatal densities drive the partitioning of conductance between leaf sides

by Fanourakis D., Giday H., Milla R., Pieruschka R., Kjaer K. H., Bolger M., Vasilevski A., Nunes-Nesi A., Fiorani F., Ottosen C.-O. (2015)

Dimitrios Fanourakis. Habtamu Giday. Rubén Milla, Roland Pieruschka, Katrine H. Kjaer, Marie Bolger, Aleksandar Vasilevski, Adriano Nunes-Nesi, Fabio Fiorani, Carl-Otto Ottosen,

IBG-2: Plant Sciences, Institute for Bio- and Geosciences, Forschungszentrum Jülich, D-52425 Jülich, Germany,

Aarhus University, Department of Food Science, Kirstinebjergvej 10, DK-5792 Årslev, Denmark,

Departamento de Biología y Geología, Área de Biodiversidad y Conservación, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, c/Tulipán s/n, Móstoles 28933, Spain,

Institute for Biology I, RWTH Aachen University, Aachen, Germany and Max Planck Partner Group at the Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-000 Viçosa, MG, Brazil

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in Ann. Bot.-London 115: 555–565 – https://doi.org/10.1093/aob/mcu247

CrossRef, Google Scholar – 

https://link.springer.com/article/10.1007/s11099-018-0847-z

Abstract

Background and Aims Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. This study aims to quantify which of these traits mainly underlie genetic differences in operating stomatal conductance (g_s) and addresses possible links between anatomical traits and regulation of pore width.

Methods Stomatal responsiveness to desiccation, g_s-related anatomical traits of each leaf side and estimated g_s (based on these traits) were determined for 54 introgression lines (ILs) generated by introgressing segments of Solanum pennelli into the S. lycopersicum‘M82’. A quantitative trait locus (QTL) analysis for stomatal traits was also performed.

Key Results A wide genetic variation in stomatal responsiveness to desiccation was observed, a large part of which was explained by stomatal length. Operating g_s ranged over a factor of five between ILs. The pore area per stomatal area varied 8-fold among ILs (2–16 %), and was the main determinant of differences in operating g_s between ILs. Operating g_s was primarily positioned on the abaxial surface (60–83 %), due to higher abaxial stomatal density and, secondarily, to larger abaxial pore area. An analysis revealed 64 QTLs for stomatal traits in the ILs, most of which were in the direction of S. pennellii.

Conclusions The data indicate that operating and maximum g_s of non-stressed leaves maintained under stable conditions deviate considerably (by 45–91 %), because stomatal size inadequately reflects operating pore area (R² = 0·46). Furthermore, it was found that variation between ILs in both stomatal sensitivity to desiccation and operating g_s is associated with features of individual stoma. In contrast, genotypic variation in g_spartitioning depends on the distribution of stomata between the leaf adaxial and abaxial epidermis.

Coordinated changes in vein and stomatal density improve the WUE of cotton under drought stress

 

 

Coordinated variation between veins and stomata in cotton and its relationship with water-use efficiency under drought stress

by Lei Z. Y., Han J. M., Yi, X. P., Zhang W. F., Zhang Y. L. (2018)

• Z. Y. Lei
• J. M. Han
• X. P. Yi
• W. F. Zhang
• Y. L. Zhang

Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Group, Agricultural College, Shihezi University, Shihezi, Xinjiang, China

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in Photosynthetica  56: 1326-1335 –  https://doi.org/10.1007/s11099-018-0847-z –

https://link.springer.com/article/10.1007/s11099-018-0847-z

Abstract

Drought stress causes changes in vein and stomatal density.

The objectives of this study were to determine

(1) if the changes in vein and stomatal density are coordinated in cotton (Gossypium hirsutum L.) and

(2) how these changes affect water-use efficiency (WUE).

The results showed significant positive correlations between vein density and stomatal density when cotton was grown under different degrees of drought stress. WUE was significantly positively correlated with the densities of both veins and stomata.

Stomatal pore area and stomatal density on the abaxial leaf side, but not the adaxial side, were significantly correlated with WUE, stomatal conductance, leaf net photosynthetic rate, and transpiration rate.

In conclusion, coordinated changes in vein and stomatal density improve the WUE of cotton under drought stress. The abaxial leaf side plays a more important role than the adaxial side in WUE and gas exchange.

New Gas Exchange Methods to Estimate Mesophyll Conductance and Non-stomatal Inhibition of Photosynthesis

 

 

Using New Gas Exchange Methods to Estimate Mesophyll Conductance and Non-stomatal Inhibition of Photosynthesis Caused by Water Deficits

by Bunce J. A. (2012)

James A. Bunce

Crop Systems and Global Change Laboratory, USDA-ARS, Beltsville Agricultural Research Center, 10300 Baltimore Avenue, Beltsville, MD 20705-2350

 

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in HortScience 47(6): 687-690 – 

http://hortsci.ashspublications.org/content/47/6/687.full

Abstract

Soil water deficits remain one of the most important factors reducing the yield of crop plants and may become even more limiting with changes in the global climate and competition for fresh water resources. Soil water deficits reduce plant growth partly by reducing photosynthesis. However, it remains unclear how important non-stomatal factors are in limiting photosynthesis under moderate water stress and whether rising atmospheric carbon dioxide may alter which processes limit photosynthesis under water stress.

The conductance to CO₂ from the substomatal air space to the site of carboxylation inside chloroplasts in C₃ plants is now termed mesophyll conductance. Because of the competition between CO₂ and O₂ for RuBisco, the carbon dioxide concentration at the chloroplast can be estimated from the O₂ sensitivity of photosynthesis, providing a new method of estimating mesophyll conductance. It has also recently been realized that partial stomatal closure resulting from water stress can often be reversed by exposing leaves to low CO₂.

This provides a new means of assessing the non-stomatal component of the inhibition of photosynthesis by water stress.

These methods were applied to four C₃ species and revealed that mesophyll conductance decreased substantially with water stress in two of the four species and that reopening of stomata did not eliminate the reduction in photosynthesis caused by moderate water stress at either the current ambient or elevated CO₂ concentrations.

Stomatal patchiness and leaf carboxylation capacity

 

 

Photosynthesis inhibition during gas exchange oscillations in ABA-treated Helianthus annuus: relative role of stomatal patchiness and leaf carboxylation capacity

by Šantrůček J., Hronkova M., Kveton J. K., Sage R. F. (2003)

J. ŠANTRŮČEK*,**,+, M. HRONKOVÁ*,**, J. KVĚTOŇ*,**, and R.F. SAGE***

* Department of Photosynthesis, Institute of Plant Molecular Biology, Academy of Sciences of the Czech Republic, Branišovská 31, CZ-370 05 České Budějovice, Czech Republic

** The University of South Bohemia, Faculty of Biology and Institute of Physical Biology, Photosynthesis Research Centre, CZ-370 05 České Budějovice, Czech Republic

*** Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada

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in PHOTOSYNTHETICA 41 (2): 241-252 –

http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Photosynthesis-inhibition-during-gas-exchange-oscillations-in-ABA-treated-Helianthus-annuus–relative-role-of-stomatal-patchiness-and-leaf-carboxylation-capacity.pdf

Abstract

Environmental factors that induce spatial heterogeneity of stomatal conductance, gs, called stomatal patchiness, also reduce the photochemical capacity of CO2 fixation, yet current methods cannot distinguish between the relative effect of stomatal patchiness and biochemical limitations on photosynthetic capacity. We evaluate effects of stomatal patchiness and the biochemical capacity of CO2 fixation on the sensitivity of net photosynthetic rate (PN) to stomatal conductance (gs), θ (θ = δPN/δgs).

A qualitative model shows that stomatal patchiness increases the sensitivity θ while reduced biochemical capacity of CO2 fixation lowers θ. We used this feature to distinguish between stomatal patchiness and mesophyll impairments in the photochemistry of CO2 fixation.

We compared gas exchange of sunflower (Helianthus annuus L.) plants grown in a growth chamber and fed abscisic acid, ABA (10–5 M), for 10 d with control plants (–ABA). PN and gs oscillated more frequently in ABA-treated than in control plants when the leaves were placed into the leaf chamber and exposed to a dry atmosphere.

When compared with the initial CO2 response measured at the beginning of the treatment (day zero), both ABA and control leaves showed reduced PN at particular sub-stomatal CO2 concentration (ci) during the oscillations. A lower reduction of PN at particular gs indicated overestimation of ci due to stomatal patchiness and/or omitted cuticular conductance, gc.

The initial period of damp oscillation was characterised by inhibition of chloroplast processes while stomatal patchiness prevailed at the steady state of gas exchange. The sensitivity θ remained at the original pre-treatment values at high gs in both ABA and control plants. At low gs, θ decreased in ABA-treated plants indicating an ABA-induced impairment of chloroplast processes.

In control plants, gc neglected in the calculation of gs was the likely reason for apparent depression of photosynthesis at low gs.

Modeling the Stomatal and Biochemical Control of Plant Gas Exchange

 

 

PHOTOBIO: Modeling the Stomatal and Biochemical Control of Plant Gas Exchange

by Wullschleger S. D., Hanson P. J., Sage R. F. (1992)

S. D. Wullschleger and P. J. Hanson, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6034;

R. F. Sage, Dep. of Botany, Univ. of Georgia, Athens, GA 30602. Publication no. 3922, Environmental Sciences Division, Oak Ridge National Laboratory

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in J. Nat. Resour. Life Sci. Educ. 21: 141-145 –

https://www.crops.org/files/publications/nse/pdfs/jnr021/021-02-0141.pdf

ABSTRACT

Simulation models are increasingly being used to describe physiological processes in the plant sciences. These models, while useful for research purposes, also offer tremendous potential for demonstrating a wide array of scientific concepts to students.

We have developed an educational software package that illustrates the stomatal and biochemical control of transpiration and photosynthesis. The simulation program uses a biochemical model of C assimilation that, when coupled to an empirical submodel describing stomatal conductance, can be solved iteratively for leaf photosynthesis, stomatal conductance, and transpiration.

Graphic and tabular presentations, combined with on-screen requests for student input, serve to effectively convey the basic fundamentals of plant gas-exchange, and the diurnal patterns of photosynthesis and transpiration in response to fluctuating environmental conditions.

More advanced topics focus on the biochemical limitations imposed on photosynthesis by Rubisco activity, electron transport capacity, and the regeneration of inorganic P. Also included is an exercise that challenges students to use the lessons learned to optimize C assimilation, while minimizing water losses, over a 3-d simulation period.

Application of the program can assist instructors in illustrating important concepts regarding stomatal and biochemical control of plant gas-exchange.

Stomatal control of transpiration

 

 

Stomatal control of transpiration in the canopy of a clonal Eucalyptus grandis plantation

by Mielke M. S., Oliva M. A., de Barrros N. F., Penchel R. M., Martinez C. A., de Almeida A. C. (1999)

M. S. Mielke · M. A. Oliva  · C. A. Martinez

Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36571-000, Viçosa, MG, Brazil; e-mail: moliva@mail.ufv.br Tel.: +55 31 899 2050; Fax: +55 31 899 2580

N. F. de Barros

Departamento de Solos, Universidade Federal de Viçosa, 36571-000, Viçosa, MG, Brazil

R. M. Penchel

Centro de Pesquisa & Tecnologia, Aracruz Celulose S.A., Aracruz, ES, 29197-000, Brazil

A. C. de Almeida

Produção e Suprimento de Madeira, Aracruz Celulose S.A., Aracruz, ES, 29197-000, Brazil&

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in Trees 13: 152–160 –

ftp://ftp.aphis.usda.gov/foia/FOLDER_10/AR00038647%20Mielke%20et%20al%201999.pdf

Abstract

Predawn leaf water potential, stomatal conductance and microclimatic variables were measured on 13 sampling days from November 1995 through August 1996 to determine how environmental and physiological factors affect water use at the canopy scale in a plantation of mature clonal Eucalyptus grandis Hill ex-Maiden hybrids in the State of Espirito Santo, Brazil.

The simple “big leaf” Penman-Monteith model was used to estimate canopy transpiration. During the study period the predawn leaf water potential varied from –0.4 to –1.3 MPa, with the minimum values observed in the winter months (June and August 1996), while the average estimated values for canopy conductance and canopy transpiration fell from 17.3 to 5.8 mm s–1 and from 0.54 to 0.18 mm h–1, respectively.

On the basis of all measurements, the average value of the decoupling coefficient was 0.25. During continuous soil water shortage a proportional reduction was observed in predawn leaf water potential and in daily maximum values of stomatal conductance, canopy transpiration and decoupling coefficient.

The results showed that water vapour exchange in this canopy is strongly dominated by the regional vapour pressure deficit and that canopy transpiration is controlled mainly by stomatal conductance.

On a seasonal basis, stomatal conductance and canopy transpiration were mainly related to predawn leaf water potential and, thus, to soil moisture and rainfall. Good results were obtained with a multiplicative empirical model that uses values of photosynthetically active radiation, vapour pressure deficit and predawn leaf water potential to estimate stomatal conductance.