"Papel da estrutura anatômica e histoquímica da casca em espécies lenhosas ripárias na resistências do fogo. "

Abstract

In the Pantanal area of Brazil, the shift from drought to flood is common and tests the adaptability of plant life. In periods of drought, the wetlands of Mato Grosso do Sul (MS) are particularly subject to wildfires caused by low relative humidity, high availability of dry organic matter, as well as burning carried out by local farmers to clear pasture land. Yet, while some tree species are completely eliminated, others survive, especially those under riparian influence. Therefore, this study aimed to evaluate the morphological and anatomical characters that could explain why some woody species in areas under the influence of the Paraguay River (MS) are resistant to fire, while others are not. To confirm the presence or absence of certain woody species, plant selection was based on floristic surveys in areas affected and not affected by fire. Specifically, the anatomy of the bark of three species considered resistant to fire, Inga vera Willd. (Fabaceae), Ocotea diospyrifolia (Meisn.) Mez (Lauraceae) and Triplaris gardneriana L. (Polygonaceae), and three nonresistant species, Albizia inundata (Mart.) Barneby & JW Grimes (Fabaceae), Genipa americana L. (Rubiaceae) and Vochysia divergens Pohl (vochysiaceae), were evaluated. The collected material was fixed in FAA 50% and stored in ethyl alcohol 70%. Specimens were embedded in polyethylene glycol and sectioned on a sliding rotary microtome in transverse, tangential and radial longitudinal planes. The sections were double stained with Alcian blue and Safranin 9:1 and mounted in permanent slides with Entellan®. From the perspectives of bark anatomy and morphology, it was found that fibrous, thick bark, including the presence of crystals and phenolic compounds, could provide fire resistance. An abundance of fibers was observed in Inga vera, and vast bands of fibers and crystals were also seen in Ocotea diospyrifolia and Triplaris gardneriana. However, while Albizia inundata presents a phloem structure similar to that of I. vera and T. americana, the amount of fibers and 13 phenol compounds is reduced in comparison to the fire-resistant species. The bark of G. americana, presenting only sclereids; druses and sand crystals are present but no phenolic compounds, were observed in the phloem of this species as well as in V. divergens. We conclude that not only the thickness of the bark but the tissue composition are important factors for fire resistance. The abundance of sclerenchyma and the presence of crystals and phenolic idioblasts, could be indicated as fire resistance elements to studied species. Species that could not resist the action of fire, did not present the set of anatomical features recognized in the first, corroborating the proposal that species were not resistant to burning.