Effects triggered by foliar selenium application on growth, enzyme activities, mineral nutrients and carbohydrates in lettuce under an aquaculture system

Effects of micro/nano-ozone bubble nutrient solutions on growth promotion and rhizosphere microbial community diversity in soilless cultivated lettuces

Due to its high efficacy as a wide-spectrum disinfectant and its potential for the degradation of pollutants and pesticides, ozone has broad application prospects in agricultural production. In this study, micro/nano bubble technology was applied to achieve a saturation state of bubble nutrient solution, including micro-nano oxygen (O2 group) and micro-nano ozone (O3 group) bubble nutrient solutions. The effects of these solutions on lettuce physiological indices as well as changes in the microbial community within the rhizosphere substrate were studied. The application of micro/nano (O2 and O3) bubble nutrient solutions to substrate-cultured lettuce plants increased the amount of dissolved oxygen in the nutrient solution, increased the lettuce yield, and elevated the net photosynthetic rate, conductance of H2O and intercellular carbon dioxide concentration of lettuce plants. Diversity analysis of the rhizosphere microbial community revealed that both the abundance and diversity of bacterial and fungal communities in the substrate increased after plant cultivation and decreased following treatment with micro/nanobubble nutrient solutions. RDA results showed that the microbial community in the S group was positively associated with EC, that in the CK and O2 groups exhibited a positive correlation with SC, and that in the O3 group displayed a positive correlation with CAT and POD. Overall, the implementation of micro/nanobubble generation technology in soilless substrates can effectively increase the lettuce growth and yield, and O3 had a more pronounced effect on lettuce yield and quality and the microbial community structure in the substrate than O2. Our study would provide a reference and theoretical basis for developing sustainable and green technology for promoting lettuce production and can be a promising alternative to conventional methods for improving crop yields.

Plant Growth-Promoting Rhizobacteria as Tools to Improve the Growth of Kohlrabi (Brassica oleracea var. gongylodes) Plants in an Aquaponics System

The use of nitrogen as a fertilizer can be highly risky when used excessively, and it is therefore necessary to find novel techniques to reduce its use. Aquaponics reduces the use of synthetic fertilizers and water, and the leaching of nitrate into the environment. One way to avoid problems due to a reduction in nitrogen availability could be the use of plant growth promoting rhizobacteria (PGPR). This study examines the effect of PGPR on kohlrabi plants grown with a traditional nutrient solution (100S), in combination with "fish water" (50F/50D), or with a supplement of synthetic fertilizers (50F/50D + S). Two formulations were used: T1 (Azospirillum brasilense and Pantoea dispersa) and T2 (Azotobacter salinestris). Irrigation with 50F/50D caused a reduction in several of the measured parameters. The combined application of 50F/50D with T1 attenuated the negative effects. T2 did not present significant effects on the parameters measured. The results obtained with 50F/50D + S hardly showed differences with the 100S. Thus, by irrigating with 50F/50D + S, we were able to maintain the yields while reducing fertilizer use and water. The combined use of T1 and 50F/50D was also positive; however, it would be necessary to continue adjusting the amount of nitrate supplied to maintain production.

Selenium in plant-based beverages: Total content, estimated bioaccessibility and contribution to daily intake

BACKGROUND

The search for alternative protein sources has increased the consumption and commercialization of plant-based beverages (PBBs). This study aimed to determine the total Se content, estimate the bioaccessibility of selenium (Se) in commercial PBBs derived from different raw materials, and evaluate their contribution to the reference daily intake (RDI).

METHODS

An ultrasound assisted acid digestion method and ICP-MS was used to determine Se, and the INFOGEST method to estimate the bioaccessible percentages. Validation of this method was also performed, and the parameters obtained were: LOD and LOQ were 2.1 and 4.0 µg/kg, respectively. For accuracy, recovery percentages ranged from 99 % and 111 % (certified reference materials), and 95 % and 101 % (spiked experiments for bioaccessible extracts as recoveries).

RESULTS

The PBBs presented total Se content between 4 and 226 µg/kg. Bioaccessible percentages ranged from 63.5 % (mix of plant sources) to 95.9 % (produced with organic cashew nuts). Only one cashew nut PBBs supplied the daily demand of Se, representing 64.6 %, 75.3 % and 82.2 % of the RDI; for lactating and pregnant women, children (≥ 4 years) and adults, respectively.

CONCLUSIONS

The Se determination method through acid digestion assisted by ultrasound and ICP-MS was considered adequate for the PBBs samples. Se content varied according to the raw material used in sample preparation. High percentages (> 60 %) of bioaccessibility were observed and only one PBBs derived from organic cashew nuts supplied the recommended Se demand for different groups of individuals.