Relações entre estrutura, química e densidade da casca com sua função em caules e raízes de espécies do cerrado paulista
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Data
2019-02-26
Autores
Vergílio, Paula Cristina Benetton [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A casca é um sistema biológico complexo que desempenha diversas funções na planta, incluindo condução de fotoassimilados, suporte mecânico, armazenamento de substâncias e proteção contra herbívoros, patógenos e intempéries como o fogo. A casca é composta, principalmente, pelo floema secundário e pela periderme, e reveste tanto caules quanto raízes. O caule está exposto à atmosfera e tem funções de elevação e suporte da planta, enquanto a raiz está exposta ao solo e tem funções de fixar a planta ao solo, armazenar substâncias e absorver e conduzir água e nutrientes. Contudo, pouco se sabe se as diferentes funções de caules e raízes indicam diferentes funções na casca de cada órgão. Neste trabalho, comparamos a casca de caules e raízes de 15 espécies representativas do cerrado paulista e testamos se a casca do caule apresentaria funções de suporte e proteção, enquanto a casca da raiz apresentaria função de armazenamento de substâncias. Também testamos se encontraríamos maior eficiência na condução de fotoassimilados na casca da raiz. Para tanto, selecionamos 15 espécies de árvores e arbustos do cerrado sensu stricto e amostramos a casca do caule e da raiz. Analisamos a estrutura (espessura e anatomia), a densidade e a química (água, açúcares solúveis, amido, nitrogênio, fósforo e carbono) e relacionamos com as funções da casca em cada órgão. Na casca do caule, encontramos maior espessura da periderme, devido ao felema mais largo com células maiores e mais espessas, e menor densidade da periderme, indicando que a casca do caule tem função de proteção contra herbívoros, patógenos e fogo. Na casca da raiz, encontramos maior espessura relativa do floema secundário e maior quantidade de açúcares solúveis, indicando que a casca da raiz possui função de armazenamento de carboidratos não-estruturais, uma estratégia importante para sobrevivência da planta no cerrado. Contudo, não encontramos evidências que apoiem nossas expectativas de função de suporte na casca do caule ou maior eficiência na condução de fotoassimilados na casca da raiz. Portanto, a casca das plantas do cerrado paulista não apresenta todas as funções desempenhadas pelo caule ou pela raiz, mas participa das funções mais importantes relacionadas à sobrevivência da planta no cerrado, como proteção contra o fogo na casca do caule e armazenamento de carboidratos não-estruturais na casca da raiz.
Bark is a complex biological system that performs multiple functions in plant, including photoassimilates conduction, mechanical support, storage and protection against herbivores, pathogens and fire. Bark comprises mainly the secondary phloem and the periderm, and covers both trunks and roots. The trunk is exposed to the atmosphere and has the main functions of plant elevation and plant support, whereas the root is exposed to the ground and has the main functions of fix the plant to the ground, store substances, provide water and nutrients to the plant. However, remain unclear whether the different functions of trunk s and roots indicate different functions in the bark of each organ. In this work, we compared the bark of trunk and roots of species in the cerrado of São Paulo, tested whether the trunk bark presents both support and protection functions, whereas the root bark presents storage function. We also tested whether we would find higher efficiency of photoassimilates conduction in the root bark. For this purpose, we selected 15 representative species of trees and shrubs in the cerrado sensu stricto and sample both trunk and root barks. We analyzed the structure (thickness and anatomy), density and chemistry (water, soluble sugars, starch, nitrogen, phosphorus and carbon) and associated to the bark functions in each organ. In the trunk bark, we found thicker periderm, due to thicker phellem with larger cell and thicker wall cells, and lower periderm density, suggesting a protection function against herbivores, pathogens and fire in trunk bark. In the root bark, we found a higher relative thickness of secondary phloem and a higher amount of soluble sugars, suggesting a nonstructural carbohydrate storage function in root bark, an important strategy for plant survival in the cerrado. However, we found no evidence to sustain our hypotheses of support function in trunk bark or higher efficiency of photoassimilates conduction in root bark. Therefore, the bark of plants in cerrado of São Paulo does not have all the functions performed by the trunk or the root, but it participates in the most important functions related to the plant survival in the cerrado, such as protection against fire in trunk bark and nonstructural carbohydrate storage in root bark.
Bark is a complex biological system that performs multiple functions in plant, including photoassimilates conduction, mechanical support, storage and protection against herbivores, pathogens and fire. Bark comprises mainly the secondary phloem and the periderm, and covers both trunks and roots. The trunk is exposed to the atmosphere and has the main functions of plant elevation and plant support, whereas the root is exposed to the ground and has the main functions of fix the plant to the ground, store substances, provide water and nutrients to the plant. However, remain unclear whether the different functions of trunk s and roots indicate different functions in the bark of each organ. In this work, we compared the bark of trunk and roots of species in the cerrado of São Paulo, tested whether the trunk bark presents both support and protection functions, whereas the root bark presents storage function. We also tested whether we would find higher efficiency of photoassimilates conduction in the root bark. For this purpose, we selected 15 representative species of trees and shrubs in the cerrado sensu stricto and sample both trunk and root barks. We analyzed the structure (thickness and anatomy), density and chemistry (water, soluble sugars, starch, nitrogen, phosphorus and carbon) and associated to the bark functions in each organ. In the trunk bark, we found thicker periderm, due to thicker phellem with larger cell and thicker wall cells, and lower periderm density, suggesting a protection function against herbivores, pathogens and fire in trunk bark. In the root bark, we found a higher relative thickness of secondary phloem and a higher amount of soluble sugars, suggesting a nonstructural carbohydrate storage function in root bark, an important strategy for plant survival in the cerrado. However, we found no evidence to sustain our hypotheses of support function in trunk bark or higher efficiency of photoassimilates conduction in root bark. Therefore, the bark of plants in cerrado of São Paulo does not have all the functions performed by the trunk or the root, but it participates in the most important functions related to the plant survival in the cerrado, such as protection against fire in trunk bark and nonstructural carbohydrate storage in root bark.
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Palavras-chave
Cerrado, casca, casca externa, casca interna, floema secundário, periderme, espessura da casca, densidade da casca, química da casca, bark, outer bark, inner bark, secondary phloem, periderm, bark thickness, bark density, bark chemistry