Análise ecofisiológica da macrófita aquática Alternanthera philoxeroides (Mart.) Griseb. no reservatório do Iraí - Pinhais, PR

Abstract

Alternanthera philoxeroides is an aquatic macrophyte native to the upper Paraná basin, capable of colonizing aquatic and terrestrial environments. Its potential for adaptation to different environmental compartments comes from its high phenotypic plasticity, conferring to the species resistance to environmental oscillations, as well as colonization strategies that favor its dispersion and establishment in the environment. The objective of this work was to characterize possible ecophysiological alterations of Alternanthera philoxeroides according to a temporal space variation in a fluctuating water supply reservoir. The study was carried out in the Iraí reservoir, located between the municipalities of Quatro Barras, Pinhais and Piraquara, metropolitan region of Curitiba. Two populations of A. philoxeroides were evaluated, one in the hydromorphic environment, and the other in the semihydromorphic. Sampling was carried out quarterly between 2017 and 2018, and the ecophysiological attributes used were: aerial biomass, photosynthetic potential, specific leaf area (SLA), leaf dry matter content (LDMC), and morphology. Biomass was quantified from dry weight of plant material per m²; photosynthetic potential was quantified by chlorophyll analysis; SLA and LDMC were calculated by measuring dry weight, fresh weight and leaf area; Morpho-anatomy measurements were made from leaves using measurements of mesophyll thickness, palisade parenchyma and diameter of the main vascular bundle of the central rib; stomatal density was obtained by counting stomata on both sides of the leaf; solar radiation, temperature and precipitation were provided by the state meteorological agency. There was spatial variation in six of the nine parameters evaluated; only SLA, LDMC and abaxial stomata density did not present significant differences between hydromorphic and semi-hydromorphic environments. There was a temporal influence on the physiological response pattern of the species. Adaptations in A. philoxeroides caused by environmental differences were more evident in the hydromorphic environment, where all ecophysiological parameters evaluated were compatible with aquatic environment physiotypes (SLA, stomatal density, palisade parenchyma and mesophyll thickness increases, central vein diameter and reduction of photosynthetic potential). The populations of this environment presented less variations in the evaluated parameters, while the semi-hydromorphic ones were the most affected by the environmental variations, presenting physiological responses compatible with both hydromorphic, transitional or terrestrial environments.