Sombreamento e aplicação de silício em mudas de Hymenaea courbaril L. sob déficit hídrico e seu potencial de recuperação

Abstract

Among the potential species for planting and recovery of degraded areas is jatobá (Hymenaea courbaril L.) a species widely distributed in the Neotropical region, tolerant to different environmental conditions. However, the low availability of water in the soil can be a limiting factor for its metabolism and growth. Thus, the use of technologies that can facilitate the increasingly used stress condition, such as the use of power silicon (K2SiO3). Therefore, the objective was to evaluate the effect of shading levels and K2SiO3 application on H. coubaril seedlings. On water deficit and the potential for photosynthetic and enzymatic metabolism recovery and seedling growth after the suspension of stress. The treatments were arranged in a completely randomized design in a split-plot scheme. The seedlings for the shading and water deficit experiment were separated into four groups based on the following water regimes. Continuous irrigation – I: 75% of the water retention capacity was maintained and Water Deficit – S, characterized by the suspension of irrigation. The water regimes were associated with the following evaluation times: F0 - when the photosynthetic rate of seedlings submitted to irrigation suspension reached values close to zero and REC - when the photosynthetic rate of seedlings that had irrigation suspended were re-irrigated and reached values similar to the control plants (at the same shading level). Thus, the treatments were as follows: Zero Photosynthesis Irrigation (IP0), Zero Photosynthesis Stress Deficit (SP0); Irrigation in Recovery (IREC), Stress in Recovery (S REC). The seedlings were allocated in 4 levels of shading: 0%, 30%, 50% and 70%. The seedlings for the K2SiO3 experiment received five doses of potassium silicate (K2SiO3) via foliar: 0.0; 3.0; 6.0; 9.0; and 12.0 mL L 1 and, later, they were submitted to two water regimes: I: irrigation performed daily and E: stress, submitted to irrigation suspension. Seedlings were evaluated in two periods: P0= photosynthesis close to zero, performed by means of daily monitoring; and REC= recovery, irrigation was resumed until the seedlings of each treatment showed photosynthesis values close to the irrigated seedlings. In both experiments activity, the characteristics of enzymes, growth, antioxidants and proline were altered. As seedlings of H. Courbaril change the sensitivity to water deficit, as there was a reduction in gas exchange, indicators of fluorescence change and the growth and quality of seedlings. When shaded and re-irrigated as previously stressed seedlings, they can recover their photosynthetic metabolism without permanent damage to the efficiency of photosystem II, and with the resumption of growth and seedling quality. The application of K2SiO3 at a dose of 6.00 mL L-1 mitigated the stressful effect on the photosynthetic apparatus and helped in the morphophysiological recovery of the seedlings. There was an increase in superoxide dismutase and peroxidase activity and protein reduction in leaves and roots with an application of K2SiO3. H. Courbaril has high resilience due to physiological plasticity. It is concluded that the shading of 30 and 50% help in mitigating the water deficit. The water deficit associated with the cultivation without shade (0%) should not be used in the cultivation or transplant of water seedlings of H. Coubaril cultivation, the application of potentiometer silica in the next dose 6.00-7.00 mL L- 1 in the increase of antioxidant enzymes, which help to mitigate the water deficit and help in the resilience of the species.