Leaf heliotropism in Styrax camporum Pohl from the Brazilian cerrado: distinct gas exchange and leaf structure, but similar leaf temperature and water relations
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Data
2008-03-01
Autores
Habermann, Gustavo [UNESP]
Machado, Silvia R. [UNESP]
Guimarães, Vandeir F.
Rodrigues, João D. [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Brazilian Journal of Plant Physiology
Resumo
Styrax camporum é uma espécie arbustiva comum dos cerrados do Estado de São Paulo, Brasil. Embora suas folhas não tenham pulvino morfologicamente delimitado, as folhas apicais são orientadas paralelamente à incidência da radiação solar (folhas paraheliotrópicas), especialmente às 1200 h. Folhas horizontais estáticas das partes basais dos ramos são orientadas perpendicularmente aos raios solares (folhas diaheliotrópicas). O significado ecofisiológico do fenômeno não foi ainda completamente elucidado. Investigou-se como o paraheliotropismo influencia a assimilação diária de CO2 (A) e outras taxas de trocas gasosas, relações hídricas, temperatura foliar (Tf) e suas relações com a estrutura da folha, avaliada por suas descrições anatômicas. Folhas paraheliotrópicas apresentaram maiores A e condutância estomática (g s), o que levou à maior taxa de transpiração (E) durante grande parte do dia. Todavia, não houve dados categóricos assegurando que estas respostas tenham determinado menor Tf para as folhas verticais, que ocorreu apenas às 1100 e 1600 h. Não houve nenhuma indicação de que Tf influenciou A, E ou g s. Entretanto, folhas diaheliotrópicas não assimilaram menos carbono por causa de estômatos mais fechados. Ambos os tipos foliares atingiram abertura estomática satisfatória e a mesma zona de resposta de g s resultou em concentrações de CO2 intercelular similares. Folhas paraheliotrópicas tiveram maior A sob elevadas irradiâncias, sugerindo evitação à elevada irradiância. em ambos tipos de folhas, observou-se parênquima esponjoso compacto, representando maior capacidade fotossintética por unidade de área foliar. O paraheliotropismo de S. camporum não parece estar relacionado ao controle da temperatura foliar, mesmo no estressante hábitat do cerrado Brasileiro.
Styrax camporum is a common shrub species from the cerrado regions of São Paulo State, Brazil. Although its leaves do not have a morphologically delimited pulvinus, the apical leaves are oriented parallel to the sun (paraheliotropic leaves), most notably around noon. Horizontal leaves at the base of shoots are oriented perpendicular to the sun's rays (diaheliotropic leaves). The ecophysiological significance of this is not fully understood. We investigated how paraheliotropism influences daily CO2 assimilation (A) and other gas exchange rates, water relations, leaf temperature (Tl), and how these relate to leaf structure as assessed by anatomical leaf descriptions. Paraheliotropic leaves had greater A and stomatal conductance (g s), which led to greater transpiration rates (E) during most of the day. However, no categorical data proved that these responses were responsible for the lower Tl for vertical leaves, which only occurred at 1100 h and 1600 h. There was no indication that Tl influenced A, E, or g s. However, diaheliotropic leaves did not assimilate less carbon because of a smaller stomatal aperture. Both leaf types had satisfactory stomatal apertures and the same g s range, resulting in similar intercellular CO2 levels. Paraheliotropic leaves had higher A rates under increased irradiance, suggesting an avoidance of excessive irradiance. Both leaf types had compact spongy parenchyma, representing an increased photosynthetic capacity per unit leaf area. Paraheliotropism in S. camporum does not seem to be related to leaf temperature control, even in the stressful Brazilian cerrado habitat.
Styrax camporum is a common shrub species from the cerrado regions of São Paulo State, Brazil. Although its leaves do not have a morphologically delimited pulvinus, the apical leaves are oriented parallel to the sun (paraheliotropic leaves), most notably around noon. Horizontal leaves at the base of shoots are oriented perpendicular to the sun's rays (diaheliotropic leaves). The ecophysiological significance of this is not fully understood. We investigated how paraheliotropism influences daily CO2 assimilation (A) and other gas exchange rates, water relations, leaf temperature (Tl), and how these relate to leaf structure as assessed by anatomical leaf descriptions. Paraheliotropic leaves had greater A and stomatal conductance (g s), which led to greater transpiration rates (E) during most of the day. However, no categorical data proved that these responses were responsible for the lower Tl for vertical leaves, which only occurred at 1100 h and 1600 h. There was no indication that Tl influenced A, E, or g s. However, diaheliotropic leaves did not assimilate less carbon because of a smaller stomatal aperture. Both leaf types had satisfactory stomatal apertures and the same g s range, resulting in similar intercellular CO2 levels. Paraheliotropic leaves had higher A rates under increased irradiance, suggesting an avoidance of excessive irradiance. Both leaf types had compact spongy parenchyma, representing an increased photosynthetic capacity per unit leaf area. Paraheliotropism in S. camporum does not seem to be related to leaf temperature control, even in the stressful Brazilian cerrado habitat.
Descrição
Palavras-chave
cerrado Brasileiro, ecofisiologia, fotossíntese, movimentos foliares, Styracaceae, temperatura foliar, trocas gasosas, Brazilian savanna, ecophysiology, gas exchange, leaf movements, leaf temperature, photosynthesis, Styracaceae
Como citar
Brazilian Journal of Plant Physiology. Brazilian Journal of Plant Physiology, v. 20, n. 1, p. 71-83, 2008.