Flooding is a stressful condition that causes damage to the photosynthetic apparatus, negatively affecting the growth of seedlings of fruit species, including Hymenaea courbaril L. Studies on physiological management, such as exogenous application of phytohormones, to alleviate abiotic stress have increased. The objective of this study was to evaluate the effect of foliar application of salicylic acid (SA) on H. courbaril seedlings subjected to flooding. The seedlings received foliar application of four concentrations of SA (0, 100, 200, and 400 mg L-1) and were subjected to two water regimes: a) control - non-flooded and irrigated daily and b) flooded - seedlings were placed in a plastic pool, keeping the water depth at ± 5.0 cm above the substrate level. After 35 days, we evaluated the gas exchange, initial growth, quality, and potential ecological resilience of the seedlings. All flooded seedlings survived, but had reduced photosynthesis, carboxylation of Rubisco efficiency, and water-use and stomatal conductance when they received 100-300 mg L-1 SA. The seedlings that received between 100 and 300 mg L-1 SA had greater growth, quality, and phenotypic plasticity. Foliar application of SA did not mitigated the effect of flooding on gas exchange but contributed to the growth of H. courbaril seedlings.
Water availability is one of the most important factors for the growth of tree seedlings in forestry-related regions. We hypothesized that under different water regimes, a waterretaining polymer (hydrogel) can positively contribute to chlorophyll-a fluorescence and growth in Campomanesia xanthocarpa (Mart.) O. Berg. Four water retention capacities (WRC) were evaluated: 25%, 50%, 75%, and 100%, depending on the presence or absence of hydrogel at the substrate. The lowest WRCs, particularly those under 25% without hydrogel, reduced chlorophyll index and negatively affected the photochemical activities of photosystem II. However, under low water availability the hydrogel mitigated the damage inflicted on the reaction centers and chlorophyll synthesis. The greatest growth effects occurred at 100% WRC in the presence of the hydrogel. Physiological indices were higher under 100% WRC without hydrogel and 50% with hydrogel. The increase in biomass and Dickson quality were more pronounced in the seedlings produced under 50% WRC and hydrogel, and the addition of these parameters to the substrate contributed to more viable morphophysiological indicators for the production of C. xanthocarpa seedlings.
The use of N fertilizers can contribute to seedling production in native species, such as Alibertia sessilis (Vell.) K. Schum, a fruit plant of the Cerrado ecoregion. Considering that there are few studies on mineral nutrition for this species, the aim of this study was to evaluate the effect of N on the growth and photosynthesis photochemical of A. sessilis. The experiment was carried out in plastic pots in a greenhouse with five N (urea) concentrations: 0, 25, 50, 75, and 100 mg kg-1. The experimental design used was a randomized block design with four repetitions. At day 180 after transplantation, morphometric and photochemical characteristics, including biomass and seedling quality, were evaluated. Seedling survival, the stem diameter of the harvest, and the height/diameter ratio were not influenced by N. The maximum height was 14.38 cm with 54.2 kg-1 N. The greatest number of leaves and value of the chlorophyll index were found in seedlings produced with maximum doses of N. The photochemical characteristics of photosynthesis, except initial fluorescence, were positively influenced with N concentrations between 60-85 mg kg-1 N. The largest fresh leaf and stem biomass was 2.391 and 0.257 g plant-1 with 54.0 and 33.0 mg kg-1 of N, respectively. The multivariate analysis of the major components explained 79.81% of the remaining data variability. The seedlings of A. sessilis responded positively during the initial growth phase, reflected in their biomass, with N concentrations close to 50.0 mg kg-1.
Water deficit to causes serious problems in the growth and development of plants, impairing their metabolism. Thus, it is necessary to use agents that can mitigate plant damage. This study assesses the potential of silicon to mitigate water deficit stress in Dipteryx alata Vogel seedlings and to help in their recovery after the resumption of irrigation. The study analyzed four water regimes: (I) Continuous irrigation; (II) Water deficit without Si; (III) Water deficit + 0.75 mL Si; and (IV) Water deficit + 1.50 mL Si. Seedlings were evaluated in four periods: (1) (T0 – time zero) at the beginning of the experiment, before irrigation suspension; (2) (P0) when the photosynthetic rates (A) of seedlings under irrigation suspension reached values close to zero, period in which irrigation was resumed; (3) (REC) when A reached values close to those of seedlings under continuous irrigation, characterizing the recovery period; and (4) (END) 45 days after REC, when seedlings were kept under continuous irrigation, similar to the control. Application of 0.75 mL Si alleviates damage to the photosynthetic apparatus of D. alata seedlings that remain longer under water deficit, and contributes to faster physiological recovery after the resumption of irrigation. D. alata seedlings have recovery potential after the stress period, regardless of Si application.
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