Estratégias adaptativas de plantas anfíbias à dinâmica hídrica do Pantanal e sua relação com a resistência ao fogo

Abstract

Submergence during flood periods and lack of water during dry periods expose aquatic and marsh plants to two opposing situations throughout the Pantanal's seasonal cycle. A major seasonally flooded area in Brazil, the Pantanal boasts a wealth of species whose pife histories are linked to fluctuations in excess and lack of water. Anoxia during flood periods can induce amphibious plants to maximize gas storage, and during dry periods, structural strategies favor their support and photosynthetic storage. Specialized underground gem systems may be part of the adaptive strategies of those plants that may lose their aerial parts and remain dormant during drought, a period when fiares may occur in wetlands. We believe that the adaptive characteristics of amphibious plants against drought may also protect them against fire, which has intensified in the Pantanal. We comparatively analyzed the adaptive structures of three amphibious species subjected to two equally stressful antagonistic factors: excess and lack of water. We collected at least three individuals of the species Aeschynomene fluminensis, Aeschynomene cf. rudis, and Discolobium pulchellum in burned and unburned areas afér. flooding, and made slides of their stems and roots. Our result. Showed that the species D. pulchellum, A. fluminensis and A. cf. rudis have potentially gem-bearing underground systems, with buds arising in the neck, main root, lateral and plagiotropic regions; plagiotropic underground stems, also gem-bearing, occur in all three species. There vãs little interspecific anatomical variation in stems and roots, with greater variation between species of the two genera studied. The fistulous stem of both Aeschynomene species, combined with adventitious roots, can supply the gas deficit during the flood period. During this period, we observed the formation of secundará aerenchyma and pith in D. pulchellum. Starch in the cortex, axial and radial parenchyma of the xylem, and phloem, and in greater quantities in the parasaval parenchyma of stems and roots, can supply the energy requirements for bud burst and maintenance of water flow in all three species. The pressente of phenolic compounds, perivascular fibers, and water reserves in the xylem and phloem parenchyma constitute the adaptive apparatus against drought, which may also favor fire protetivo in these species. However, the aerial parts of A. fluminensis are more sensitive to fire, libele due to the chemical composition and thinner structure of the stem. The structural and histochemical adaptations to flooding and dry periods obtained for the three amphibious plant species evaluated are also efficient for protection against the deleterious actions of fog.