Silício e sombreamento atenuam os efeitos do déficit hídrico no metabolismo e no crescimento foliar de mudas de Dipteryx alata Vog

Abstract

One of the great challenges to be overcome in the coming years by native tree species in the Cerrado are the abiotic stresses, mainly water deficit, which hinders the growth and development of plants in this biome. Thus, it is necessary to use technologies that can mitigate the damage caused to plants by this stress. The aim of this study was to evaluate the physiological and morphoanatomical behavior of Dipteryx alata seedlings subjected to water deficit, silicon doses and the use of shading levels. For this, the study was divided into two experiments reported in two chapters. In the first chapter, four water regimes were studied: Continuous irrigation – I: Water deficit – II + 0,00 mL of Si, Water deficit + 0,75 mL of Si and Water deficit + 1,50 mL of Si. The seedlings were evaluated in four periods: (1) (T0 – time zero) beginning of the experiment, period before starting the irrigation suspension; (2) (F0) when the values of t photosynthesis (A) in seedlings under suspension of irrigation reached zero, with the resumption of irrigation; (3) (REC) A values close to those of the seedlings under continuous irrigation, characterizing the recovery and (4) (POS-REC) 45 days after the REC when the seedlings were kept under continuous irrigation, similar to the control. The application of 0,75 mL of Si provides a decrease in damage to the photosynthetic apparatus of D. alata seedlings for a longer period under water deficit, and contributes to a faster physiological recovery after resuming irrigation. During the POS-REC all the seedlings recovered their physiological and growth potential. In the second chapter, the seedlings were separated into three groups and transferred to nurseries under three shade levels: 0 (full sun), 30 and 70% shade. In each shading, the seedlings received three water regimes: Continuous irrigation – C, Suspension of irrigation and Suspension of irrigation + application of 0,75 mL Si. For the characterization of photosynthetic metabolism, the seedlings were evaluated at T0 – time zero at the beginning of the experiment, period before starting the suspension of irrigation. After the suspension of irrigation, the seedlings were evaluated in two periods: when the values of photosynthesis (A) in the seedlings under suspension of irrigation reached zero, when irrigation was resumed, and when photosynthesis reached values close to that of the seedlings. Under continuous irrigation, recovery. The interaction between shading and silicon mitigated the stressful effect of water deficit during water restriction in D. alata seedlings, since they delayed the reduction of photosynthesis and anticipated its recovery. During water deficit, 70% shading independent of silicon maintained the SPAD index and chlorophyll a fluorescence characteristics with similar or higher values and with less reduction in the relative water content of the leaves. All the evaluated characteristics recovered after irrigation resumption, except the Rubisco carboxylation efficiency (A/Ci), regardless of the treatments.