Potencial do silício e sombreamento em induzir a tolerância e recuperação de mudas de Eugenia myrcianthes Nied. (Myrtaceae) ao estresse hídrico

Abstract

The planting of native forest species to enrich forests and recover degraded areas is still limited by the lack of information on the ideal conditions for seedling production and performance. Some plants in low water conditions, due to irregular rainfall, may be susceptible to morphophysiological damage. On the other hand, excess water, for certain periods, becomes an aggravating factor for species not adapted to flooded environments. Diante da degradação do Cerrado, aliada às mudanças climáticas, estudos sobre a produção de mudas nativas, associados a metodologias que permitam que essas mudas sobrevivam em condições climáticas adversas, tornam-se necessários e podem viabilizar projetos de restauração de áreas degradadasConsidering the importance of Eugenia myrcianthes for the Cerrado biome, the objective of this work was to evaluate the potential for recovery of photosynthetic and enzymatic metabolism and growth of seedlings submitted to conditions of water stress. Two experiments were conducted. In the first experiment, the responses of species exposed to different levels of shading in mitigating water deficit were evaluated. For the shading study, the seedlings were submitted to two water regimes (continuous irrigation and suspended irrigation) combined with three levels of shading (0, 30 and 70%) and evaluations in four moments: T0 - beginning of the evaluations and subsequent suspension of the irrigation; P0 - when the photosynthetic rate of seedlings in some shading level, submitted to irrigation suspension, reached values close to zero, with subsequent re-irrigation; Rec - when the photosynthetic rate of the seedlings that had irrigation suspended and were re-irrigated, reached values similar to those of the control and FINAL plants to evaluate the development of the seedlings after recovery, which occurred 92 days after recovery. In the second experiment, the effect of silicon was evaluated on seedlings submitted to water fluctuation (water deficit and flooding) after the suspension of stress. The seedlings were separated into six groups based on the following water regimes: Continuous irrigation – I: 75% of the water retention capacity in the substrate, Water stress – E: suspension of irrigation and subsequent flooding. Water regimes were associated with three silicon concentrations: 0; 2 and 4 mmol L-1. The seedlings were evaluated in five periods: Time zero (T0) - beginning of evaluations and suspension of irrigation; First zero photosynthesis under water deficit (1st P0); First recovery – (1st Rec); Second zero photosynthesis under flooding (2nd P0); Second recovery (2nd Rec). E. myrcianthes seedlings are sensitive to both water deficit and full sun, which impairs the development of seedlings, impairing the photochemical and biochemical metabolism of photosynthesis, increasing the activity of antioxidant enzymes, reducing root growth and seed quality . seedlings. However, the 30% shading attenuated the stressful effects of water deficit and favored a faster recovery of some characteristics. The application of silicon at concentrations of 2 mmol L-¹ attenuated the effect of water stress, favoring the development of seedlings and tolerance to water fluctuation, although some characteristics evaluated recovered independently of the presence of silicon. These results suggest that this species has physiological plasticity that facilitates the adjustment to stressful environmental conditions in this growth phase.