Padrões espectrais de reflectância foliar e sua relação com o status hídrico em uma floresta de terra firme na Amazônia Central

Abstract

Tropical forests play an important role in regulating water cycles, carbon and energy flows. Thus, studies that address both ecological and physiological aspects (ecophysiology) are necessary to understand how water availability affects the maintenance of these ecosystems. In this scenario, spectroscopy in the visible (VIS) and infrared (VIS-NIR) regions has emerged as a fast and non-destructive tool for obtaining information on the water status of plant organs and tissues. Previous studies have shown that, in the Central Amazon, plateau species are more adapted to drought conditions and therefore invest in a more resistant hydraulic system, with a smaller average vessel diameter and smaller sapwood area when compared to species found in lowland areas. In addition to the influence of topography and soil type on the hydraulic characteristics of species, canopy position and wood density can also influence these hydraulic functional traits. It is known, for example, that species with low wood density have greater hydraulic vulnerability when compared to species with high density, due to the different trade-offs that these two functional groups have. Low-density species (commonly associated with pioneer plants) invest the assimilated carbon in growth, while high-density species (commonly associated with climax plants) invest the carbon in reserves. In this context, the main objective of this work was to investigate the relationship between water status and leaf spectral reflectance of tree species with different wood densities and with exclusive occurrence in a plateau area in Central Amazonia. The main criterion for selecting species was the wood density spectrum. Spectral readings were taken on mature leaves of different species using an ASD FieldSpec 3 spectroradiometer, together with the acquisition of pressure-volume curve data and leaf functional traits such as leaf water content, specific leaf mass and nitrogen content. A Genie Z80/60 lifting platform (crane) with a vertical reach of around 26 meters was used to collect the leaves. The initial results showed no significant differences in leaf traits between the high and low density groups. However, spectroscopy showed that there are differences in ecological strategies for the functional groups (low and high density). The reflectance data along the pressure-volume curve suggested that high-density wood species are more tolerant of water stress, with a lower turgor loss point and higher leaf water content. With regard to leaf traits, leaf water content had significant correlations with short-wave infrared (1300-2400 nm). Specific leaf mass was most sensitive to the short-wave infrared region (1300-2400 nm). The spectral indices evaluated were sensitive to leaf functional traits and the point of turgor loss. From this work, we hope to gain a better understanding of vegetation spectral behavior and its relationship with plant functional characteristics.