Silício: alívio a estresses abióticos em ambientes naturais

Abstract

Silicon (Si) has long been ignored by plant ecologists. However, their participation in terrestrial ecosystems is undeniable. The hypothesis of this work is that plants in natural environments are subjected to isolated or combined abiotic stresses that can stimulate the uptake of Si. Thus, these plants are also benefited by the absorption and accumulation of the element. In this way, the following predictions were made: I) The concentrations of silicon available in the soil solution would increase the spatial distribution and consequent biomass production of plants, favoring their occupation in areas with limiting conditions, II) plant populations located in environments with adverse edaphoclimatic conditions that result in physiological stresses in the plant will have the greater absorption and accumulation of silicon in order to develop mechanisms of resistance to established physiological stress. To test these predictions, the Eugenia punicifolia species, with a wide geographic distribution, was selected and occupies three different phytophysiognomies with limiting abiotic conditions in the State of Ceará: Coastal Savanna, Seasonal Deciduous Forest, and Dense Deciduous Shrub. Initially, it was studied whether the species presented dormancy or germination characteristics that indicated an acclimatization of the same to their places of origin. Subsequently, a meta-analysis was carried out with the published articles dealing with the stress-damaging effects of Si, in order to identify if their effects are proven, if there are variations in response to the element between species, if the positive results are corroborated over of the time and if there are advances in the knowledge about the mechanisms of stress relief by the element. Experiments were conducted in a laboratory and greenhouse to simulate climatic conditions of stresses common to the areas selected for this study and evaluated the Si absorption, tissue concentration and biomass production of plants. Finally, these same parameters were analyzed in field, on the three phytophysiognomies, in order to identify structural and/or physiological changes caused by the Si in plants under stress under natural conditions, and if these would facilitate the understanding of the mechanisms of relief to abiotic stresses in ecological studies. It was observed that the species presents adaptation to the climate of its natural habitat, which helps to understand its wide colonization in climatically distinct environments. It was confirmed in studies with Si, that there are no differences in the responses to the types of stress (water and temperature) at which the plants are submitted, which gives a more general effect of the element. In addition, the main novelty is that the smoothing effect of the element has been decreasing over the years of study on it. In the laboratory, it was observed that the absorption of Si by the studied species is increased by water stress and temperature variations when the plants originate fromphytophysiognomies with higher availability of Si in the soil. Finally, under natural conditions, the plants of E. punicifolia absorb more Si from the soil when stimulated by the presence of limiting factors, reflecting once again, adaptations to their places of origin. Thus, this study allows inferring Si stress relief functions in natural systems, confirming the benefits of the element already discussed for agricultural crops.