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Caracterização da capacidade fotossintética e da condutância estomática em sete clones comerciais de Eucalyptus e seus padrões de resposta ao déficit de pressão de vapor; Photosynthetic capacity and stomatal conductance characterization for seven commercial Eucalyptus clones and their variation due to vapor pressure deficit

Marrichi, Ana Heloisa Carnaval
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/03/2009 PT
Relevância na Pesquisa
66.57%
O estudo caracterizou as variáveis fisiológicas da fotossíntese, em 7 clones de Eucalyptus de alta produtividade, determinando-se as capacidades fotossintéticas máximas (Amax), e o comportamento da fotossíntese (A), condutância (gs) e transpiração (E) em relação ao Déficit de Pressão de Vapor (DPV). Para isso, um ensaio foi instalado em 2004, na ESALQ/USP, contendo os clones do Projeto BEPP (Brasil Eucalyptus Produtividade Potencial), sendo cada parcela composta de 49 plantas (7x7) no espaçamento de 3,0m x 2,7m. Mediram-se as alturas ou DAPs e selecionaram-se 3 árvores médias para as mensurações fisiológicas, aos 16 e 36 meses. A amostragem para Amax foi composta de duas posições superiores da copa (2 e 3), dois galhos por posição e duas folhas por galho. As medições foram feitas das 8 às 10 horas (baixo DPV). Para o comportamento de A e gs frente ao DPV, as medições continuaram, de hora em hora, das 11 às 15 horas, nas folhas do primeiro galho da posição 2. Ao final as folhas foram coletadas para determinação da área foliar específica (AFE) e do nitrogênio (N). Aos 16 meses, foram feitas curvas A/Ci, para posterior cálculo de Vcmax (taxa máxima de carboxilação), Jmax (taxa máxima de transporte de elétrons) e VTPU (utilização da triose fosfato)...

Caracterização da capacidade fotossintética e da condutância estomática em árvores de Pinus caribaea var. hondurensis e de Pinus taeda em Itatinga, São Paulo; Characterization of photosynthetic capacity and stomatal conductance in trees of Pinus caribaea var. hondurensis and Pinus taeda in Itatinga, São Paulo

Carneiro, Rafaela Lorenzato
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/08/2013 PT
Relevância na Pesquisa
66.57%
Realizaram-se campanhas em árvores de cinco anos de idade de Pinus caribaea var. hondurensis e Pinus taeda em parcelas controle (sem fertilização e sem irrigação) e parcelas fertilizadas e irrigadas, durante o verão e o inverno de 2012 visando caracterizar as seguintes variáveis fisiológicas: i) Capacidade máxima fotossintética (Amax); ii) Fotossíntese ao longo do dia (A); iii) Variação da condutância estomática (gs) em relação ao aumento do déficit de pressão de vapor (DPV); e iv) Taxas máximas de carboxilização (Vcmax) e de transporte de elétrons (Jmax) via curvas A/Ci. O estudo foi realizado no projeto Produtividade Potencial do Pinus no Brasil, localizado na Estação Experimental da ESALQ/USP em Itatinga-SP.Foram escolhidas três árvores médias por parcela para as avaliações fisiológicas, realizadas com o LiCor 6400XT. A mensuração da Amax foi realizada no terço médio da copa, em dois galhos por árvore e em duas posições por galho, sendo realizada das 8 às 10 horas, e o comportamento da A, gs com o aumento do DPV, ocorreram de hora em hora, das 11 às 15 horas. Ao final, as acículas foram coletadas para a determinação da área foliar específica (AFE) e do nitrogênio foliar. As curvas A/Ci foram realizadas nas três árvores...

O papel da histerese no comportamento  complexo da condutância estomática; The role of hysteresis in the complex behavior of the stomatal conductance

Ramos, Antônio Mário de Torres
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 21/02/2013 PT
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66.86%
Estômatos são poros responsáveis pela troca gasosa entre a folha e o meio externo. A partir da década de 80, experimentos revelaram um complexo padrão espaço temporal na abertura e fechamento dos estômatos. As experiências apontam para uma possível coordenação entre estômatos em algumas áreas da folha chamada de patches. Esse fenômeno é conhecido na literatura como patchy stomatal conductance. Frequentemente a coordenação dinâmica dos estômatos está associada à oscilações temporais na condutãncia estomática (média especial da abertura dos estômatos). Em 1997 Haefner, Buckley e Mott (HBM) publicaram uma análise numérica de um modelo dinâmico para explorar o comportamento complexo dos estômatos. O modelo é baseado em algumas características conhecidas dos estômatos e assume transporte hídrico em uma rede definida por uma geometria simples e bastante restritiva. De acordo com os autores, o modelo reproduz qualitativamente os dados experimentais. Recentemente, Ferraz e Prado mostraram que esse modelo não é capaz de reproduzir os resultados experimentais. Usando ingredientes do modelo sugerido por HBM, Ferraz e Prado sugeriram uma geometria realística de distribuição reservatórios hídricos. Embora essa configuração reproduza os patches...

Grapevine varieties exhibiting differences in stomatal response to water deficit

Costa, Joaquim M.; Ortunõ, Maria F.; Lopes, Carlos M.; Chaves, M.M.
Fonte: CSIRO Publicador: CSIRO
Tipo: Artigo de Revista Científica
Publicado em //2012 ENG
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56.67%
Abstract. Knowledge on variety traits and physiological responses to stress is still scarce in Vitis vinifera L., limiting the optimisation of irrigation and breeding for high water use efficiency. We have characterised five grapevine varieties using thermal imaging, leaf gas exchange, leaf morphology and carbon isotope composition. Plants of the varieties Aragonez, Trincadeira, Cabernet Sauvignon, Syrah and Touriga Nacional were grown in field conditions. Two experiments were performed. In Experiment I (2006), vines of Aragonez and Trincadeira were either well irrigated (WI, 80% ETc), nonirrigated but rain fed (NI) or subjected to regulated deficit irrigation (RDI, 40% ETc) and studied along the summer season. In Experiment II (2006 and 2007), vines of the five varieties were subjected to RDI (30–40% ETc) and studied at veraison. In Experiment I, leaf temperature (Tleaf) correlated negatively with stomatal conductance (gs) and leaf water potential (Ypd). The inverse relationship between gs and Tleaf was highly significant in the afternoon. In Experiment II, the different genotypes showed different Tleaf for similar Ypd. Stomatal density did not correlate with gs suggesting that varieties have different stomatal control. Our results show that combined measurements of canopy temperature and Ypd can aid in better understanding of stomatal regulation in different grapevine varieties. Such variation in stomatal regulation should be taken into account in determining irrigation strategies

Comparing water relations and stomatal regulation of Touriga Nacional and Syrah under mild water stress

Lopes, Carlos; Monteiro, Ana; Chaves, M.M.
Fonte: Universidade Técnica de Lisboa Publicador: Universidade Técnica de Lisboa
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
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56.56%
Proceedings - IX International Terroir Congress, 2012; Aiming to compare the physiological responses of the Portuguese red variety Touriga Nacional (TN) with Syrah (SY), we studied during the 2007 growing season five-year-old grapevines growing in a commercial non-irrigated vineyard located at the Lisbon winegrowing region. Predawn (Ypd) and midday (YM) leaf water potential, leaf stomatal conductance (gs) and photosynthetic rate (A) were periodically measured between fruit set and harvest. Ypd displayed a decreasing pattern throughout the growing cycle from -0.10 MPa at flowering to -0.44 MPa at harvest. Both varieties showed similar values except during the two measurements made in August when TN presented significantly higher values than SY. Ymid also showed a decreasing pattern from the end of June towards harvest date, with significant differences between varieties being observed during the ripening period, with SY showing lower values than TN. A measured either at mid-morning and midday presented, for most part of the cases, lower values in SY than in TN, although the differences were only significant during the ripening period. gs pattern was parallel to A and, in general, the relative differences between varieties mirrored those reported for A. No significant effect of the variety was detected on the relationships between A or gs measured at mid-morning and Ypd. However...

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight12[C][W][OA]

Boccalandro, Hernán E.; Giordano, Carla V.; Ploschuk, Edmundo L.; Piccoli, Patricia N.; Bottini, Rubén; Casal, Jorge J.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
EN
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46.88%
Leaf epidermal peels of Arabidopsis (Arabidopsis thaliana) mutants lacking either phototropins 1 and 2 (phot1 and phot2) or cryptochromes 1 and 2 (cry1 and cry2) exposed to a background of red light show severely impaired stomatal opening responses to blue light. Since phot and cry are UV-A/blue light photoreceptors, they may be involved in the perception of the blue light-specific signal that induces the aperture of the stomatal pores. In leaf epidermal peels, the blue light-specific effect saturates at low irradiances; therefore, it is considered to operate mainly under the low irradiance of dawn, dusk, or deep canopies. Conversely, we show that both phot1 phot2 and cry1 cry2 have reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday. These mutants show compromised responses of stomatal conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely nonstomatic. While the stomatal conductance phenotype of phot1 phot2 was blue light specific, cry1 cry2 showed reduced stomatal conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid were elevated in cry1 cry2. We conclude that considering their effects at high irradiances cry and phot are critical for the control of transpiration and photosynthesis rates in the field. The effects of cry on stomatal conductance are largely indirect and involve the control of abscisic acid levels.

Temperature responses of mesophyll conductance differ greatly between species

von Caemmerer, Susanne; Evans, John R.
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.77%
The temperature responses of mesophyll conductance (gm ) were investigated for nine species using carbon isotope techniques combining tunable diode laser spectroscopy and gas exchange measurements. Species included the evergreen trees Eucalyptus pauciflora and Quercus engelmannii; the tropical evergreen tree Lophostemon confertus; as well as the herbaceous species Nicotiana tabacum, Oryza sativa, Triticum aestivum, Gossypium hirsutum, Glycine max and Arabidopsis thaliana. Responses varied from a two- to threefold increase in mesophyll conductance between 15 and 40 °C observed for N. tabacum, G. hirsutum, G. max and E. pauciflora to almost no change in L. confertus and T. aestivum. To account for the different temperature responses between species, we suggest that there must be variation in both the activation energy for membrane permeability and the effective pathlength for liquid phase diffusion. Stomatal conductance was relatively independent of increases in leaf temperature and concomitant increases in leaf to air vapour pressure difference. Two exceptions were Eucalyptus and Gossypium, where stomatal conductance increased with temperature up to 35 °C despite increasing leaf to air vapour pressure. For a given species...

Consumo de água em plantios de eucalipto: parte 1 determinação da condutância estomática em tratamentos irrigado e não-irrigado; Water consumption in eucalypt plantation: part 1 determination of stomatal conductance in irrigated and non-irrigated treatments

CARNEIRO, Rogério Lessa de Castro; RIBEIRO, Aristides; MARTINEZ Y HUAMAN, Carlos Alberto; LEITE, Fernando Palha; SEDIYAMA, Gilberto Chohaku; BASTOS, Nairam Felix de
Fonte: Sociedade de Investigações Florestais Publicador: Sociedade de Investigações Florestais
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
66.86%
Devido ao grande interesse sobre a necessidade hídrica em cultivos de eucalipto e qual a resposta da planta às condições ambientais, esta pesquisa teve como objetivo calcular o consumo de água em plantios de eucalipto com 2 anos de idade. O trabalho foi composto por duas partes, sendo a primeira dedicada à determinação da condutância estomática em clones de Eucalyptus grandis x Eucalyptus urophylla irrigados e não-irrigados e à verificação do efeito da variação sazonal das varáveis ambientais. A segunda parte compreendeu a modelagem da resistência estomática e o cálculo da transpiração pelo método de Penman-Monteith. O sítio experimental localizava-se no Município de Belo Oriente, Estado de Minas Gerais, a 19(0)18'23" S de latitude, 42(0)22'46" W de longitude e 220 m de altitude. Na primeira parte, a condutância estomática foi medida em três períodos diferentes: período úmido, início do período seco e período seco. Valores médios da condutância estomática variando entre 0,41 e 0,22 mol m-2 s-1 no plantio irrigado e entre 0,38 e 0,24 mol m-2 s-1 no não-irrigado foram encontrados. Também, verificou-se que a condutância estomática sofreu variação entre os períodos úmido e seco, a qual foi relacionada com algumas variáveis ambientais e umidade do solo.; In response to the growing interest in hydric need in eucalypt plantations and plant response as a function of environmental conditions...

The role of Physphoenolpyruvate Carboxylase during C 4 Photosynthetic Isotope Exchange and Stomatal Conductance

Cousins, Asaph; Baroli, Irene; Badger, Murray; Ivakov, Alexander; Lea, Peter J; Leegood, Richard C; von Caemmerer, Susanne
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.49%
Phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) plays a key role during C4 photosynthesis and is involved in anaplerotic metabolism, pH regulation, and stomatal opening. Heterozygous (Pp) and homozygous (pp) forms of a PEPC-deficient mutant of the C4

Acclimatory responses of stomatal conductance and photosynthesis to elevated CO2 and temperature in wheat crops grown at varying levels of N supply, in a Mediterranean environment.

Del Pozo, Alejandro; Pérez, P.; Morcuende, R.; Alonso, Aitor; Martínez-Carrasco, R.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 251491 bytes; application/pdf
ENG
Relevância na Pesquisa
66.57%
The short and long-term responses of flag leaf stomatal conductance (gs) and rate of photosynthesis (An) to elevated CO2 (757 μmol mol-1), 4 ºC warmer temperatures and N supply were investigated in spring wheat (Triticum aestivum L. cv. Alcalá) crops grown in two seasons in field conditions under temperature gradient tunnels, in a Mediterranean environment. Plants grown at elevated CO2 had lower gs and An measured at 700 μmol mol-1 CO2 than ambient CO2-grown plants, indicating acclimatory responses to elevated CO2. N supply, which was lower in 2003 than 2002, reduced this acclimation in both years. Warmer temperatures at high nitrogen supply also decreased An acclimation. Acclimatory responses of An and gs were highly correlated. The analysis of the gs – An relationship indicated that both parameters are probably linked and respond in parallel to elevated CO2 at ambient temperatures, but non-parallel responses were observed at above-ambient temperatures.; This work was funded by the Spanish Programme of Research and Development (grant No. BFI2000-0871). A. Del Pozo was the recipient of a fellowship from the Spanish Ministry of Education for a sabbatical leave. R. Morcuende had a Ramón y Cajal research contract from the Spanish Ministry of Education. The technical cooperation of A.L. Verdejo in gas exchange measurements and chlorophyll determination is acknowledged. We thank the staff of the experimental farm of IRNASA for assistance in crop husbandry.; Peer reviewed

Effects of reafforestation techniques on the nutrient content, photosynthetic rate and stomatal conductance of Pinus Halepensis seedlings under semiarid conditions

Díaz, Elvira; Roldán Garrigos, Antonio
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
66.57%
A field experiment was carried out to evaluate the effect of different soil preparation techniques for Pinus halepensis afforestation on physiological parameters in Mediterranean summer conditions. The soil preparation treatments consisted of terracing (mechanical and manual) and the addition of an organic amendment (urban solid refuse). The mycorrhizal treatments consisted of nursery inoculation with Pisolithus arhizus and the addition of forest soil to the planting holes. Six years after planting the study revealed significant differences in heights and basal diameters, phosphorus and potassium concentrations in the leaves and photosynthetic rate and stomatal conductance. The pines grown in the manually prepared terraces were subjected to strong water stress, as reflected by the high A:gs ratios and highest levels of phosphorus and potassium in leaves. Mechanical terracing and the addition of urban solid refuse produced a higher photosynthetic rate, and a combination of these treatments was particularly effective; null; Peer reviewed

Responses of two semiarid conifer tree species to reduced precipitation and warming reveal new perspectives for stomatal regulation

García Forner, Núria; Henry D. Adams; Sevanto, Sanna; Collins, Adam D.; Dickman, Lee T.; Hudson, Patrick J.; Zeppe, Melanie; Martínez Vilalta, Jordi; McDowell, Nate G.
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/acceptedVersion
Publicado em //2015; 2015 ENG
Relevância na Pesquisa
56.69%
Relatively anisohydric species are predicted to be more predisposed to hydraulic failure than relatively isohydric species, as they operate with narrower hydraulic safety margins. We subjected co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis trees to warming, reduced precipitation, or both, and measured their gas exchange and hydraulic responses. We found that reductions in stomatal conductance and assimilation by heat and drought were more frequent during relatively moist periods, but these effects were not exacerbated in the combined heat and drought treatment. Counter to expectations, both species exhibited similar gs temporal dynamics in response to drought. Further, whereas P. edulis exhibited chronic embolism, J. monosperma showed very little embolism due to its conservative stomatal regulation and maintenance of xylem water potential above the embolism entry point. This tight stomatal control and low levels of embolism experienced by juniper refuted the notion that very low water potentials during drought are associated with loose stomatal control and with the hypothesis that anisohydric species are more prone to hydraulic failure than isohydric species. Because direct association of stomatal behaviour with embolism resistance can be misleading...

The effect of exogenous abscisic acid on stomatal development, stomatal mechanics, and leaf exchange gas in Tradescantia virginia

Franks, Peter Joseph; Farquhar, Graham
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.91%
Gas exchange parameters and stomatal physical properties were measured in Tradescantia virginiana plants grown under well-watered conditions and treated daily with either distilled water (control) or 3.0 mM abscisic acid (ABA). Photosynthetic capacity (CO2 assimilation rate for any given leaf intercellular CO2 concentration [ci]) and relative stomatal sensitivity to leaf-to-air vapor-pressure difference were unaffected by the ABA treatment. However, at an ambient CO2 concentration (ca) of 350 μmol mol-1, ABA-treated plants operated with significantly lower ci. ABA-treated plants had significantly smaller stomata and higher stomatal density in their lower epidermis. Stomatal aperture versus guard cell pressure (Pg) characteristics measured with a cell pressure probe showed that although the form of the relationship was similar in control and ABA-treated plants, stomata of ABA-treated plants exhibited more complete closure at Pg = 0 MPa and less than half the aperture of stomata in control plants at any given Pg. Scaling from stomatal aperture versus Pg to stomatal conductance versus Pg showed that plants grown under ABA treatment would have had significantly lower maximum stomatal conductance and would have operated with lower stomatal conductance for any given guard cell turgor. This is consistent with the observation of lower ci/ca in ABA-treated plants with a ca of 350 μmol mol-1. It is proposed that the ABA-induced changes in stomatal mechanics and stomatal conductance versus Pg characteristics constitute an improvement in water-use efficiency that may be invoked under prolonged drought conditions.

Nocturnal stomatal conductance and implications for modelling (delta oxygen 18) of leaf-respired CO2 in temperate tree species

Barbour, Margaret M; Cernusak, Lucas; Whitehead, David; Griffin, Kevin; Turnbull, Matthew H; Tissue, David T; Farquhar, Graham
Fonte: CSIRO Publishing Publicador: CSIRO Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.78%
Variation in the oxygen isotope composition of within-canopy CO2 has potential to allow partitioning of the ecosystem respiratory flux into above- and below-ground components. Recent theoretical work has highlighted the sensitivity of the oxygen isotope composition of leaf-respired CO2 (δRl) to nocturnal stomatal conductance. When the one-way flux model was tested on Ricinus communis L. large enrichments in δRl were observed. However, most species for which the isotope flux partitioning technique has been or would be applied (i.e. temperate tree species) are much more conservative users of water than R. communis. So, high stomatal conductance and very high enrichment of δRl observed may not be typical for temperate tree species. Using existing gas-exchange measurements on six temperate tree species, we demonstrate significant water loss through stomata for all species (i.e. statistically significantly greater than cuticular loss alone) at some time for some leaves during the night. δRl values predicted by the one-way flux model revealed that δRl might be very much more enriched than when the net flux alone is considered, particularly close to sunrise and sunset. Incorporation of the one-way flux model into ecosystem respiration partitioning studies will affect model outputs and interpretation of variation in the oxygen isotope composition of atmospheric CO2.

How should leaf area, sapwood area and stomatal conductance vary with tree height to maximize growth?

Buckley, Thomas; Roberts, David W
Fonte: Heron Publishing Publicador: Heron Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.57%
Conventional wisdom holds that the ratio of leaf area to sapwood area (L/S) should decline during height (H) growth to maintain hydraulic homeostasis and prevent stomatal conductance (gs) from declining. We contend that L/S should increase with H based on a numerical simulation, a mathematical analysis and a conceptual argument: (1) numerical simulation - a tree growth model, DESPOT (Deducing Emergent Structure and Physiology Of Trees), in which carbon (C) allocation is regulated to maximize C gain, predicts L/S should increase during most of H growth; (2) mathematical analysis - the formal criterion for optimal C allocation, applied to a simplified analytical model of whole tree carbon-water balance, predicts L/S should increase with H if leaf-level gas exchange parameters including gs are conserved; and (3) conceptual argument - photosynthesis is limited by several substitutable resources (chiefly nitrogen (N), water and light) and H growth increases the C cost of water transport but not necessarily of N and light capture, so if the goal is to maximize C gain or growth, allocation should shift in favor of increasing photosynthetic capacity and irradiance, rather than sustaining gs. Although many data are consistent with the prediction that L/S should decline with H...

Stomatal conductance does not correlate with photosynthetic capacity in transgenic tobacco with reduced amounts of Rubisco

von Caemmerer, Susanne; Lawson, Tracy; Oxborough, Kevin; Baker, Neil; Andrews, Thomas; Raines, Christine
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.83%
High-resolution imaging of chlorophyll a fluorescence from intact tobacco leaves was used to compare the quantum yield of PSII electron transport in the chloroplasts of guard cells with that in the underlying mesophyll cells. Transgenic tobacco plants with reduced amounts of Rubisco (anti-Rubisco plants) were compared with wild-type tobacco plants. The quantum yield of PSII in both guard cells and underlying mesophyll cells was less in anti-Rubisco plants than in wild-type plants, but closely matched between the two cell types regardless of genotype. CO2 assimilation rates of anti-Rubisco plants were 4.4 μmol m-2 s-1 compared with 17.3 μmol m-2 s-1 for the wild type, when measured at a photon irradiance of 1000 μmol m-2 s-1 and ambient CO2 of 380 μmol mol-1. Despite the large difference in photosynthetic capacity between the anti-Rubisco and wild-type plants, there was no discernible difference in the rate of stomatal opening, steady-state stomatal conductance or response of stomatal conductance to ambient CO2 concentration. These data demonstrate clearly that the commonly observed correlation between photosynthetic capacity and stomatal conductance can be disrupted in the long term by manipulation of photosynthetic capacity via antisense RNA technology. It was concluded that stomafal conductance is not directly determined by the photosynthetic capacity of guard cells or the leaf mesophyll.

Optimal stomatal control in relation to leaf area and nitrogen content

Farquhar, Graham; Buckley, Thomas; Miller, Jeffrey
Fonte: Suomen Geologinen Seura Publicador: Suomen Geologinen Seura
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.69%
We introduce the simultaneous optimisation of water-use efficiency and nitrogen-use efficiency of canopy photosynthesis. As a vehicle for this idea we consider the optimal leaf area for a plant in which there is no self-shading among leaves. An emergent result is that canopy assimilation over a day is a scaled sum of daily water use and of photosynthetic nitrogen display. The respective scaling factors are the marginal carbon benefits of extra transpiration and extra such nitrogen, respectively. The simple approach successfully predicts that as available water increases, or evaporative demand decreases, the leaf area should increase, with a concomitant reduction in nitrogen per unit leaf area. The changes in stomatal conductance are therefore less than would occur if leaf area were not to change. As irradiance increases, the modelled leaf area decreases, and nitrogen/leaf area increases. As total available nitrogen increases, leaf area also increases. In all the examples examined, the sharing by leaf area and properties per unit leaf area means that predicted changes in either are less than if predicted in isolation. We suggest that were plant density to be included, it too would further share the response, further diminishing the changes required per unit leaf area.

Gene action for leaf conductance in three wheat crosses

Rebetzke, G J; Condon, Anthony G; Richards, Robert I; Farquhar, Graham
Fonte: CSIRO Publishing Publicador: CSIRO Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.77%
Selection for altered stomatal conductance has potential to improve wheat grain yields in dry and well-watered environments. Yet the slow speed with which conductance is typically measured has limited studies reporting genetic parameters for leaf conductance. A viscous air-flow porometer that measures resistance to mass flow through a leaf was used to provide rapid estimates of leaf conductance. These estimates were obtained prior to anthesis on irrigated plants representing different generations of crosses between the low conductance parent, Quarrion, and 3 high conductance varieties, Hartog, Genaro 81, and Matong. Sampling for leaf conductance was done between 08 00 and 12 00 hours under cloud-free conditions. Significant (P < 0.01) genetic differences were observed between generation means for conductance measured in different crosses and on different days. Gene action was complex with both additive and non-additive (dominance and additive-based epistasis) genetic effects important for expression of leaf conductance. There was a greater reduction in leaf conductance for Quarrion and backcross-Quarrion progeny with sampling later into the day. In turn, genetic variances for leaf conductance increased with later sampling. Family-mean heritabilities varied in size (0.06-0.70)...

A hydromechanical and biochemical model of stomatal conductance

Buckley, Thomas; Mott, K A; Farquhar, Graham
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.83%
A mathematical model of stomatal conductance is presented. It is based on whole-plant and epidermal hydromechanics, and on two hypotheses: (1) the osmotic gradient across guard cell membranes is proportional to the concentration of ATP in the guard cells; and (2) the osmotic gradient that can be sustained per unit of ATP is proportional to the turgor pressure of adjacent epidermal cells. In the present study, guard cell [ATP] is calculated using a previously published model that is based on a widely used biochemical model of C3 mesophyll photosynthesis. The conductance model for Vicia faba L. is parameterized and tested As with most other stomatal models, the present model correctly predicts the stomatal responses to variations in transpiration rate, irradiance and intercellular CO2. Unlike most other models, however, this model can predict the transient stomatal opening often observed before conductance declines in response to decreases in humidity, soil water potential, or xylem conductance. The model also explicitly accommodates the mechanical advantage of the epidermis and correctly predicts that stomata are relatively insensitive to the ambient partial pressure of oxygen, as a result of the assumed dependence on ATP concentration.

Carbon-water balance and patchy stomatal conductance.

Buckley, Thomas; Farquhar, Graham; Mott, K A
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
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Stomata govern carbon-water balance by simultaneously controlling photosynthesis (A) and transpiration (E). It is unclear how patchy stomatal conductance influences this control. Cowan and Farquhar showed that for a given water supply available during a fixed time interval, carbon gain is maximized by a pattern of stomatal behavior that keeps the partial derivative of A with respect to E constant. This result implies that spatially uniform stomatal conductance is optimal (provided photosynthetic performance and environmental conditions are spatially uniform), so patchy stomatal conductance should be detrimental to carbon-water balance. However, these results required that the curvature of A versus E be uniformly negative. Using mathematical arguments and computer modeling, we show that (1) this caveat is violated under some environmental conditions, (2) water-use efficiency (A/E) is nearly unaffected, and can actually be improved, by patchiness under these conditions, and (3) patchiness has most often been observed under conditions similar to these. These results imply that under many conditions, patchiness may not significantly influence carbon-water balance, consistent with recent work suggesting patchiness may be common but unobserved. Additionally...