Estudos do habitat e das relações ecológicas da espécie microendêmica Nicotiana gandarela Augsten & Stehmann (Solanaceae) revelam a importância da conservação da geodiversidade no Quadrilátero Ferrífero

Abstract

Microendemic and/or endangered species, with little knowledge about their ecological requirements, need urgent investment in research to support conservation guidelines. The subject of this study is the microendemic species Nicotiana gandarela Augsten & Stehmann, Solanaceae family, which occurs exclusively in the locality of André do Mato Dentro, Serra da Gandarela, Santa Bárbara, MG, Brazil. The general objective was to characterize the phenology, ecophysiological aspects, elementome, environmental requirements of the species, in order to identify the main environmental factors/filters involved in its microendemic character, as well as its current distribution of occurrences. The phenological studies covered the reproductive and vegetative phenophases, every two weeks for 17 months. At the same time, the microclimatic variables of air humidity and temperature were recorded using a datalogger in order to identify possible phenological associations with the microclimatic variables. For the ecophysiological studies, the light intensity and light spectrum were characterized using a spectrometer, with three measurements during the day, 8am, 12pm and 3pm. Gas exchange analysis was carried out using a portable infrared gas analyzer (IRGA), with a 6 cm² aperture camera coupled with an LED light source. The electron transport rate (ETR) in relation to light intensity was obtained from rapid light curves using a fluorometer. The specific leaf area (SFA) was calculated based on leaf area (LA) and leaf dry mass (DM), using the formula SFA = LA/MD, with leaf area obtained through photography and digital image processing. The photosynthesizing pigments were extracted in DMSO (Dimethylsulphoxide) stored in amber glasses for 48 hours in dark conditions and at room temperature (22 ± 2 ºC) and quantified in a spectrophotometer reader for the following wavelengths: 480, 649 and 665nm. The content of total chlorophylls (Ca+b), the ratio between chlorophyll a and b (Ca/b), and the ratio between chlorophylls and carotenoids (total chlorophyll/carotenoids) were also calculated. For comparative soil analyses, samples were obtained from the microhabitats of the known populations, as well as from similar environments in the Serra da Gandarela, with the presence of dolomite outcrops, during the search for new population records. With regard to the phenological profile, the species had a higher proportion of annual individuals, with reproductive phenology concentrated in the dry season, with a certain phenological lag between subpopulations and individuals evaluated. A potential association of most of the phenophases was identified with the air humidity variable, and the other variables were eliminated due to the occurrence of multicollinearity. The rarity of the species is linked to its evolutionary and restrictive adaptation to intensely shaded environments formed by carbonate (domolitic) rock outcrops, in which the soil has high ph, magnesium and silt values. The results of the soil analysis and other characteristics of the microhabitats studied, together with the evidence obtained for the elementome of N. gandarela, indicate the potential existence of a highly specialized floristic community (dolomitophytes) and singular in the complex of dolomitic outcrops and dolomitic marbles of the Gandarela formation distributed in the Iron Quadrangle.