Plasticidade fenotípica em miconia ligustroides (dc.) naudin (melastomataceae) em cerrado stricto sensu e floresta estaciomal semidecídua: dados morfoanatômicos, histoquímicos e fisiológicos
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2020-02-21
Autores
Valerio, Zoraide
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Universidade Estadual Paulista (Unesp)
Resumo
A busca pela compreensão dos mecanismos que permitem que espécies vegetais ocupem ambientes distintos tem atraído a atenção de inúmeros pesquisadores, especialmente no contexto de mudanças climáticas. Neste sentido, características morfológicas, anatômicas e fisiológicas têm sido usadas com frequência para investigar respostas das plantas a diferentes condições ambientais. Miconia ligustroides, um representante de Melastomataceae, exibe extremo polimorfismo em cerrado (stricto sensu) e floresta estacional semidecídua (Mata Atlântica). Com o objetivo de verificar como as características foliares variam nesta espécie em reposta ao ambiente, e compreender como essas respostas podem interferir na distribuição da espécie em ambientes contrastantes, exemplares de M. ligustroides foram estudados e comparados. Para isso, amostras de folhas completamente expandidas foram coletadas e processadas para estudos aos microscópios de luz e eletrônico de varredura, de acordo com técnicas usuais. Trocas gasosas, fluorescência da clorofila a e luminosidade incidente foram avaliadas in loco utilizando-se o analisador de gás infravermelho portátil (IRGA-modelo LI 6400 XT, Li-cor). Foram realizados registros do microclima e análises físico-químicas do solo nas áreas de estudo. Plantas desses dois ambientes mostraram variações quanto ao hábito e características morfológicas e anatômicas das folhas, além de diferenças nos índices de trocas gasosas e fluorescência da clorofila a. No cerrado, as plantas apresentaram hábito arbustivo, com limbo espesso e de coloração esverdeada-brilhante, dispostas verticalmente nos ramos. Na floresta, as plantas apresentaram porte arbóreo, com limbo delgado e coloração verde-escura opaco, dispostas horizontalmente nos ramos. Cutícula mais espessa com estrias cuticulares e ceras epicuticulares em forma de placas proeminentes, células epidérmicas e células do parênquima paliçádico mais altas e mesofilo mais espessos foram observados nos exemplares do cerrado. Braquiesclereides ocorreram unicamente na nervura principal dos exemplares do cerrado; idioblastos cristalíferos contendo mucilagem e células com conteúdo fenólico foram observados em todos os exemplares analisados, contundo foram mais abundantes no cerrado. Não houve diferença significativa em relação à densidade e diâmetro (polar e equatorial) dos estômatos entre os dois ambientes. Nas plantas do cerrado, foram registradas as maiores taxas de assimilação liquida de CO2, transpiração, condutância estomática, eficiência da enzima Rubisco e menor concentração interna de CO2, enquanto que a eficiência do uso da água não diferiu estatisticamente nas duas localidades. Os maiores valores de rendimento quântico efetivo do fotossistema II (ΦFSII), taxa de transporte de elétrons (ETR), quenching fotoquímico (qP), fração de luz absorvida pela antena do fotossistema II que é dissipada como calor (D), foram registrados em plantas de M. ligustroides do cerrado. Maiores valores de fração de energia de excitação não dissipada na antena que não pode ser utilizada na fotoquímica (Ex) e maior rendimento quântico potencial do fotossistema II (Fv'/Fm') foram registrados em plantas de M. ligustroides na floresta. O presente estudo demonstrou que as características morfológicas, anatômicas e fisiológicas variam entre os exemplares de M. ligustroides ocorrendo em cerrado e floresta e, o conjunto de resultados obtidos neste estudo indica que as variações exibidas por M. ligustroides estão relacionadas principalmente com as condições de luminosidade do ambiente, que é significativamente mais elevada no cerrado, e com algumas características físico-químicas do solo, principalmente a elevada concentração de manganês no solo da floresta. A capacidade de M. ligustroides em explorar ambientes com diferenças significativas na intensidade luminosa e características do solo pode 2 explicar sua ampla distribuição em diferentes ecossistemas e pode ser vantajoso em condições de mudanças ambientais. Finalmente, a análise comparada de características morfoanatômicas e fisiológicas de folhas em representantes de M. ligustroides do cerrado e floresta, juntamente com registro das condições edafoclimáticas dessas duas fitofisionomias forneceu uma base para definir os fatores que atuam na plasticidade fenotípica desta espécie.
The search for understanding the mechanisms that allow plant species to occupy different environments has attracted the attention of countless researchers, especially in the context of climate change. In this sense, morphological, anatomical and physiological characteristics have been used frequently to investigate plant responses to different environmental conditions. Miconia ligustroides, a representative of Melastomataceae, exhibits extreme polymorphism in cerrado (stricto sensu) and seasonal semideciduous forest (Atlantic Forest). In order to verify how the leaf characteristics vary in this species in response to the environment, and to understand how these responses can interfere in the distribution of the species in contrasting environments, specimens of M. ligustroides were studied and compared. For this, samples of fully expanded leaves were collected and processed for studies under light and scanning electron microscopes, according to usual techniques. Gas exchanges, chlorophyll a fluorescence and incident luminosity were evaluated on the spot using the portable infrared gas analyzer (IRGA-model LI 6400 XT, Li-cor). Records of the microclimate and physical-chemical analyzes of the soil in the study areas were carried out. Plants from these two environments showed variations in habit and morphological and anatomical characteristics of the leaves, in addition to differences in gas exchange rates and chlorophyll a fluorescence. In the cerrado, the plants showed a shrubby habit, with a thick, bright greenish-colored limb, arranged vertically on the branches. In the forest, the plants were arboreal in size, with a thin limb and a dark green opaque color, horizontally arranged on the branches. Thicker cuticle with cuticular streaks and epicuticular waxes in the form of prominent plaques, higher epidermal cells and palisade parenchyma cells and thicker mesophyll were observed in the cerrado specimens. Brachiesclereides occurred only in the main vein of the cerrado specimens; Crystalline idioblasts containing mucilage and cells with phenolic content were observed in all specimens analyzed, however they were more abundant in the cerrado. There was no significant difference regarding the density and diameter (polar and equatorial) of the stomata between the two environments. In the cerrado plants, the highest rates of net CO2 assimilation, transpiration, stomatal conductance, efficiency of the Rubisco enzyme and lower internal CO2 concentration were recorded, while the efficiency of water use did not differ statistically in the two locations. The highest values of effective quantum yield of photosystem II (ΦFSII), electron transport rate (ETR), photochemical quenching (qP), fraction of light absorbed by photosystem II antenna that is dissipated as heat (D), were recorded in plants of M. ligustroides from the cerrado. Higher values of fraction of excitation energy not dissipated in the antenna that cannot be used in photochemistry (Ex) and higher potential quantum yield of photosystem II (Fv '/ Fm') were recorded in plants of M. ligustroides in the forest. The present study demonstrated that the morphological, anatomical and physiological characteristics vary between the specimens of M. ligustroides occurring in cerrado and forest, and the set of results obtained in this study indicates that the variations exhibited by M. ligustroides are mainly related to the conditions of brightness of the environment, which is significantly higher in the cerrado, and with some physical-chemical characteristics of the soil, mainly the high concentration of manganese in the forest soil. The ability of M. ligustroides to explore environments with significant differences in light intensity and soil characteristics can explain its wide distribution in different ecosystems and can be advantageous in conditions of environmental change. Finally, the comparative analysis of morphoanatomical and physiological characteristics of leaves in representatives of M. ligustroides from the cerrado and forest, together with a record of the edaphoclimatic conditions of these two phytophysiognomies provided a basis for defining the factors that act on the phenotypic plasticity of this species.
The search for understanding the mechanisms that allow plant species to occupy different environments has attracted the attention of countless researchers, especially in the context of climate change. In this sense, morphological, anatomical and physiological characteristics have been used frequently to investigate plant responses to different environmental conditions. Miconia ligustroides, a representative of Melastomataceae, exhibits extreme polymorphism in cerrado (stricto sensu) and seasonal semideciduous forest (Atlantic Forest). In order to verify how the leaf characteristics vary in this species in response to the environment, and to understand how these responses can interfere in the distribution of the species in contrasting environments, specimens of M. ligustroides were studied and compared. For this, samples of fully expanded leaves were collected and processed for studies under light and scanning electron microscopes, according to usual techniques. Gas exchanges, chlorophyll a fluorescence and incident luminosity were evaluated on the spot using the portable infrared gas analyzer (IRGA-model LI 6400 XT, Li-cor). Records of the microclimate and physical-chemical analyzes of the soil in the study areas were carried out. Plants from these two environments showed variations in habit and morphological and anatomical characteristics of the leaves, in addition to differences in gas exchange rates and chlorophyll a fluorescence. In the cerrado, the plants showed a shrubby habit, with a thick, bright greenish-colored limb, arranged vertically on the branches. In the forest, the plants were arboreal in size, with a thin limb and a dark green opaque color, horizontally arranged on the branches. Thicker cuticle with cuticular streaks and epicuticular waxes in the form of prominent plaques, higher epidermal cells and palisade parenchyma cells and thicker mesophyll were observed in the cerrado specimens. Brachiesclereides occurred only in the main vein of the cerrado specimens; Crystalline idioblasts containing mucilage and cells with phenolic content were observed in all specimens analyzed, however they were more abundant in the cerrado. There was no significant difference regarding the density and diameter (polar and equatorial) of the stomata between the two environments. In the cerrado plants, the highest rates of net CO2 assimilation, transpiration, stomatal conductance, efficiency of the Rubisco enzyme and lower internal CO2 concentration were recorded, while the efficiency of water use did not differ statistically in the two locations. The highest values of effective quantum yield of photosystem II (ΦFSII), electron transport rate (ETR), photochemical quenching (qP), fraction of light absorbed by photosystem II antenna that is dissipated as heat (D), were recorded in plants of M. ligustroides from the cerrado. Higher values of fraction of excitation energy not dissipated in the antenna that cannot be used in photochemistry (Ex) and higher potential quantum yield of photosystem II (Fv '/ Fm') were recorded in plants of M. ligustroides in the forest. The present study demonstrated that the morphological, anatomical and physiological characteristics vary between the specimens of M. ligustroides occurring in cerrado and forest, and the set of results obtained in this study indicates that the variations exhibited by M. ligustroides are mainly related to the conditions of brightness of the environment, which is significantly higher in the cerrado, and with some physical-chemical characteristics of the soil, mainly the high concentration of manganese in the forest soil. The ability of M. ligustroides to explore environments with significant differences in light intensity and soil characteristics can explain its wide distribution in different ecosystems and can be advantageous in conditions of environmental change. Finally, the comparative analysis of morphoanatomical and physiological characteristics of leaves in representatives of M. ligustroides from the cerrado and forest, together with a record of the edaphoclimatic conditions of these two phytophysiognomies provided a basis for defining the factors that act on the phenotypic plasticity of this species.
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Palavras-chave
Anatomia, Foliar, Cerrado, Floresta, Fluorescência, Clorofila, , Miconia, Plasticidade, Fenotípica, Fotossíntese, Variação, Anatômica