Efeito mitigador do silicato de potássio, extrato de algas e Bacillus subtilis no potencial de recuperação de mudas de Cedrela fissilis Vell., sob estresse hídrico

Abstract

Global climate change has made morphophysiological and biochemical alterations in plants more frequent in response to abiotic stresses. In this context, water limits plant development due to increased water deficits and extreme flooding. This scenario reinforces the need to deepen ecophysiological knowledge for the production of high-quality forest seedlings. Thus, strategies are sought to mitigate metabolic damage and increase tolerance to water fluctuations. The use of biostimulants emerges as an alternative to increase plant resilience, with potassium silicate acting in structural and water support, algae extract in metabolic-hormonal balance, and B. subtilis in root promotion and resistance induction. Therefore, the present study aimed to evaluate the morphophysiological, biochemical, and antioxidant metabolisms of Cedrela fissilis Vell. seedlings. This study aimed to evaluate the effects of water stress on seedlings subjected to different water conditions, as well as their recovery potential, and to determine if the application of potassium silicate, seaweed extract (Ascophyllum nodosum), and B. subtilis, alone or in combination, can mitigate the effects of water stress. In the first experiment, seedlings were subjected to flooding, with or without the application of mitigators, and growth, gas exchange, photochemical efficiency, and antioxidant activity were evaluated during stress and after the recovery phase. It was found that flooding significantly compromised the photosynthetic metabolism and growth of untreated seedlings, while the application of mitigators promoted greater maintenance of the photosynthetic rate, recovery of stomatal conductance, and stability of the photosynthetic apparatus. Potassium silicate stood out for promoting structural integrity and photochemical efficiency, while inoculation with B. subtilis contributed to morphological and osmotic adjustments, resulting in greater preservation of leaf architecture. In the second experiment, seedlings were subjected to water fluctuation, characterized by alternating water deficit, rehydration, and subsequent flooding, associated or not with the application of potassium silicate and B. subtilis. It was observed that the initial water deficit promoted a significant reduction in photosynthetic activity, stomatal closure, and limitation of gas exchange, regardless of the application of mitigators at that time. However, during recovery and subsequent flooding stress, it became evident that the treatments with potassium silicate and bacteria reconfigured the physiological response of the seedlings, conferring greater tolerance to sequential stress. Potassium silicate contributed to membrane stability and reduced dependence on intense enzymatic antioxidant responses, while B. subtilis favored osmotic adjustment and biomass maintenance. The activity of antioxidant enzymes revealed a high metabolic cost associated with the history of stress in untreated seedlings, while the mitigators allowed for more balanced and efficient responses. Overall, the results demonstrate that C. fissilis is sensitive to variations in water availability, but exhibits high physiological plasticity when subjected to appropriate management strategies. The application of potassium silicate and B. subtilis proved efficient in mitigating damage caused by isolated or sequential water stresses, promoting complementary mechanisms of tolerance and recovery. These results reinforce the importance of adopting mitigating practices even in the nursery phase, aiming at the production of more resilient seedlings with greater survival potential in environments subject to water instability.