Efeito da variação da profundidade do lençol freático nos traços hidráulicos, na fenologia e no incremento diamétrico de Aldina heterophylla Spruce ex Benth. em campinarana Amazônica

Abstract

Campinaranas are white sand ecosystems with nutrient-poor soils, which may have shallow or deep water tables, depending on the level of soil pedogenesis. The vegetation of this environment is composed of species with some degree of tolerance to water stress, providing opportunities for the occurrence of endemic species. The macucu (Aldina heterophylla Spruce ex Benth.) is a specialist species of this ecosystem, occurring throughout the depth variation of the campinaranas water table, and is considered a model species for studies aimed at understanding the adaptations of vegetation to environmental gradients. Therefore, it is hypothesized that seasonal variation in soil water levels influences the adjustment of the functional and hydraulic characteristics of the species. Thus, we sought to verify: how phenology and seasonal variation of the gradient relate to the pattern of increase; and how the functional traits of adaptation to drought of the species vary. For this purpose, the monthly rates of diameter increase with dendrometric bands and reproductive and vegetative phenological observations were monitored from September 2023 to August 2024 in 30 trees in reproductive state. Of these, 10 were in humid campinarana (CU), 10 in intermediate campinarana (CI) and 10 in dry campinarana (CS), located in the Uatumã Sustainable Development Reserve (RDSU), classified according to previous data from the PELD-MAUA II project. Fifteen of these trees that were already being monitored were sampled, 5 in each category of soil water availability, collecting data on water potential at noon, maximum vessel length, parenchyma and vessel cell areas, branch density and crown diameter. The biomass/basal area ratio, average annual increment, total height, pot vulnerability index, height/diameter ratio and hydraulic safety margin were also analyzed through principal component analysis, ANOVA, regression, circular statistics and path analysis in the R software. It was observed that there was no difference in phenophases and increment between the physiognomies studied. The vegetative phenophases presented asynchronous behavior, and the reproductive phenophases, synchronous behavior, suggesting that there may be an exchange of genetic material in the population. The length of the day and irradiation were significant factors for the occurrence of new leaves in the population. During the rainy season, flowering, fruiting and an increase in the monthly increment of the species occur, the latter may be related to bark swelling during this period. Of the traits analyzed, only height, biomass/basal area ratio, pot area/height and crown diameter showed significant differences between the environments, with CS showing lower divergent values than CU and CI, which showed convergent characteristics. Thus, the dominant species in the RDSU campinaranas can probably perform genetic exchange regardless of the gradient, and the adjustment that the species makes to occur in the gradient of variation in the depth of the water table indicates that it remains safe in the face of atypical climate events. Longer monitoring times are recommended to allow for a more holistic analysis in future studies. Studies on the conservation of the species in the face of anthropogenic pressures on ecosystems are also suggested.