Distribuição de espécies com folhas homobáricas e heterobáricas no Cerrado e na Floresta Estacional Semidecídua
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Data
2016-02-16
Autores
Mendes, Katiane Reis [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Em folhas de diversas espécies vegetais, a bainha de células que envolve os feixes vasculares se estende em direção à epiderme em ambas as faces do limbo formando extensões da bainha do feixe (EBF), o que caracteriza folhas heterobáricas. Folhas que não apresentam EBF são chamadas homobáricas. Pesquisas demostram que folhas homobáricas garantem maior difusão lateral de gases, enquanto as EBF podem atuar na condução de água e aumentar o desempenho fotossintético foliar garantindo a transferência de luz para as camadas mais internas do mesofilo. As diferenças morfofuncionais entre os dois tipos foliares parecem estar relacionadas ao ambiente onde as plantas ocorrem e à sua distribuição nos diferentes estratos vegetacionais. Entretanto, para formações vegetais no Brasil não foram encontrados estudos sobre a distribuição de espécies com folhas homobáricas e heterobáricas. Esse trabalho teve como objetivo estudar a anatomia foliar de espécies herbáceas, arbustivas e arbóreas na floresta estacional semidecídua, cerradão e cerrado stricto sensu a fim de identificar folhas homobáricas e heterobáricas, buscando associar a presença/ausência de EBF com o porte das plantas e com o ambiente. Quadrantes de 20mX20m foram demarcados nas fragmentos vegetacionais. Folhas completamente expandidas foram coletadas de 59 espécies no cerradão (32 arbóreas; 19 arbustos e 8 herbáceas); 68 espécies no cerrado stricto sensu (21 arbóreas; 30 arbustos e 17 herbáceas) e 51 espécies na floresta estacional semidecídua (23 arbóreas; 17 arbustos e 11 herbáceas). Amostras do limbo foliar foram processadas segundo técnicas usuais em anatomia vegetal. Nossos resultados sugerem que, embora espécies com folhas homobáricas sejam predominantes em todos os ambientes estudados, espécies com folhas heterobáricas são mais comuns no Cerrado, podendo as EBF estar associadas ao uso eficiente da água nesse ambiente. Embora não tenhamos encontrado uma relação direta entre porte das plantas e tipo foliar, parece existir uma tendência a maior abundância de espécies com folhas heterobáricas entre as de maior porte. Dentre as espécies com folhas heterobáricas, a maioria apresenta EBF constituídas por células de esclerênquima, principalmente no Cerrado, o que pode colaborar no suporte e proteção das folhas contra o colapso em condições de deficiência hídrica e mineral e alta radiação solar. Em consonância com nossos resultados, dados fisiológicos poderão auxiliar a interpretação do papel das EBF no desempenho fotossintético das espécies analisadas e sua relação com a distribuição das espécies nos diferentes ambientes.
In leaves of several plants species, the vascular bundle sheath extends toward the epidermis on both sides of the blade forming bundle sheath extensions (BSE), characterizing heterobarics leaves. Leaves lacking BSE are called homobarics. Research shows that homobaric leaves provide greater lateral movements of gases, while the BSE can act conducting water and increasing the leaf photosynthetic performance, what ensures the transference of light to the inner layers of the mesophyll. The morphological and functional differences between the two leaf types seem to be related to the environment where the plants occur and their distribution in the different vegetation strata. However, there are no studies on the distribution of species with homobarics and heterobarics leaves for vegetation formations in Brazil. This work aimed to study the leaf anatomy of herbs, shrubs and trees in semideciduous seasonal forest, cerradão and cerrado stricto sensu to identify homobarics and heterobarics leaves, searching to associate the presence / absence of BSE to the plant strata and environmental characteristics. Quadrants of 20mX20m were marked in vegetation fragments. Fully expanded leaves were collected from 59 species in the cerradão (32 tree, 19 shrubs and 8 herbs); 68 species in the cerrado stricto sensu (21 tree, 30 shrubs and 17 herbs) and 51 species in the semideciduous seasonal forest (23 tree, 17 shrubs and 11 herbs). Samples of the leaf blade were processed according to standard techniques in plant anatomy. Our results suggest that, while species with homobarics leaves predominate in all the studied environments, species with heterobarics leaves are more common in the Cerrado, and the BSE may be associated with the efficient use of water in this environment. Although we have not found a direct relationship between the plant habit and the leaf type, there seems to be a tendency to greater abundance of species with heterobarics leaves among the higher strata. Among the species with heterobarics leaves, the most of them presents EBF composed of sclerenchyma cells, especially in the Cerrado, which can assist in the support and protection of leaves against the collapse in conditions of water and mineral deficiency and high sun radiation. In consonance with our results, physiological data can help the interpretation of the role of EBF in the photosynthetic performance of the analyzed species and its relation to the distribution of species in different environments.
In leaves of several plants species, the vascular bundle sheath extends toward the epidermis on both sides of the blade forming bundle sheath extensions (BSE), characterizing heterobarics leaves. Leaves lacking BSE are called homobarics. Research shows that homobaric leaves provide greater lateral movements of gases, while the BSE can act conducting water and increasing the leaf photosynthetic performance, what ensures the transference of light to the inner layers of the mesophyll. The morphological and functional differences between the two leaf types seem to be related to the environment where the plants occur and their distribution in the different vegetation strata. However, there are no studies on the distribution of species with homobarics and heterobarics leaves for vegetation formations in Brazil. This work aimed to study the leaf anatomy of herbs, shrubs and trees in semideciduous seasonal forest, cerradão and cerrado stricto sensu to identify homobarics and heterobarics leaves, searching to associate the presence / absence of BSE to the plant strata and environmental characteristics. Quadrants of 20mX20m were marked in vegetation fragments. Fully expanded leaves were collected from 59 species in the cerradão (32 tree, 19 shrubs and 8 herbs); 68 species in the cerrado stricto sensu (21 tree, 30 shrubs and 17 herbs) and 51 species in the semideciduous seasonal forest (23 tree, 17 shrubs and 11 herbs). Samples of the leaf blade were processed according to standard techniques in plant anatomy. Our results suggest that, while species with homobarics leaves predominate in all the studied environments, species with heterobarics leaves are more common in the Cerrado, and the BSE may be associated with the efficient use of water in this environment. Although we have not found a direct relationship between the plant habit and the leaf type, there seems to be a tendency to greater abundance of species with heterobarics leaves among the higher strata. Among the species with heterobarics leaves, the most of them presents EBF composed of sclerenchyma cells, especially in the Cerrado, which can assist in the support and protection of leaves against the collapse in conditions of water and mineral deficiency and high sun radiation. In consonance with our results, physiological data can help the interpretation of the role of EBF in the photosynthetic performance of the analyzed species and its relation to the distribution of species in different environments.
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Palavras-chave
Anatomia foliar, Cerradão, Cerrado stricto sensu, Floresta estacional semidecídua, Extensão da bainha de feixe, Porte, Bundle sheath extension, Habit, Leaf anatomy, Semideciduous seasonal forest