Respostas ecofisiológicas de comunidades vegetais em áreas de cerrado rupestre a variações espaço-temporais e sazonais

Abstract

The growth, development and contribution of savannas, as in other vegetation’s formations, are conditioned by nutritional availability, water seasonality and greater exposure to the incidence of solar radiation, mainly in the rocky environment. In the Cerrado, in rocky environments, plant species have to deal with poor macronutrients, shallow and high aluminum saturation (Al3+) soils. Some species preventing its absorption and others creating aluminum mechanisms internal tolerance, and being able to accumulate more than 1000 mgkg-1Al in their plant tissues. Usually, most Al-accumulating species occur in dystrophic soils, such as those under sanditic influence, but they can also occur in meso-eutrophic soils, such as the rupicolous ones found in limestone outcrops, characterized by high nutritional contents, but also by high seasonal water deficits. In this context, we seek to understand how limestone and sandstone Neosols seasonally modulate photosynthetic activities and leaf water states in two Al-accumulating Vochysiaceae, i.e. Qualea parviflora Mart. and Callisthene fasciculata Mart., with different preferences. In addition, we also studied, through remote sensing techniques, the leaf phenology of shrub-tree communities in two rocky cerrados occupying limestone (CC) and sandstone (CA) outcrops. In this study, we showed that CC phenology, in the rainy season, was characterized by greater leaf growth. While in the dry season, in the same cerrado, there was variation in senescence in the short and long term, unlike the CA, which varied in the long term. It was also possible to show that the phenology of the CC is more affected by the water deficit, in relation to the CA, and that temperature is the factor that most explains the phenological patterns of the two rocky cerrados studied by us. As for the water status of the two savannah communities, on average, the CC showed higher values of leaf moisture (UF), in relation to the CA, in both seasons. However, CA registered the highest UF between 2011 and 2021, in the dry season. Additionally, we show that temperature was the main climate factor that modulates UF, varying with temperature and precipitation variation. As for the ecophysiology of the two species mentioned above, we first observed that the edaphic conditions did not reflect on the leaf chemistry, except on the P concentrations for both species. We observed that Q. parviflora was submitted to more stressful conditions in sandstone soil, mainly in the dry season, however, PSII was more active in this same soil in the rainy season. On the other hand, C. fasciculata confirmed intolerance to water deficit in calcareous soil due to its low quantum yield, but showed greater photosystem II activity in the dry season. We showed that photosynthetic rates responded to water seasonality and soil type, when Q. parviflora showed greater photosynthetic performance in sandstone soil in the rains, being regulated in the dry season. While C. fasciculata was less tolerant to water deficit in calcareous soil, but was more efficient in photosynthetic regulation in that same soil. Finally, it was possible to verify that each species has its own physiological plasticity to deal with periods of drought in eutrophic and dystrophic soils.