Assessing changes in growth, yield, and rhizosphere microbiome of red beetroot (Beta vulgaris subsp. vulgaris var. conditiva) cultivated under a saline integrated vegeculture-aquaculture system

In the past decade, red beetroot (Beta vulgaris L. ssp. vulgaris) has attracted the scientific community's attention as a functional food due to its essential biochemical properties for improving human health. Consequently, there has been an increase in the human and industrial demand for this crop, hence a growing interest in sustainable agricultural technologies to increase production. This study, therefore, aimed to investigate changes in the growth, yield, and rhizosphere microbiome of red beetroot cultivated in a saline integrated vegeculture-aquaculture system (IVAS). The study followed a completely randomized design of four salinity treatments: T1: 4.7 dSm−1, T2: 7.5 dSm−1, T3: 11.25 dSm−1, and T4: control (fresh water, 0.63 dSm−1) with four replicates. The study’s results indicated that salinity negatively affected plant growth (plant height, leaf number, leaf length, leaf width, leaf shape index) and yield (leaf fresh and dry weights, root fresh weight, and root diameter), with the lowest values recorded in T3 and T2. Likewise, T3 and T2 recorded the lowest values for the relative water content at 15 days after transplanting compared to T1 and T4. Nutrient analysis indicated higher magnesium, zinc, and manganese content in red beetroot cultivated in T1, T2, and T3. On the other hand, results of the rhizosphere microbiome indicated that salinity influenced the abundance and diversity of bacteria and archaea species in the IVAS. Proteobacteria and Euryarchaeota were the dominant bacterial and archaeal phyla across all the salinity treatment groups. At the class level, Gammaproteobacteria were dominant in T1, T2, and T3, whereas T4 exhibited a variation in the dominance of different bacterial classes. For archaea, the dominant classes were Thermoprotei in T1 and T3, unclassified Euryarchaeota and unclassified archaea in T2, and unclassified archaea in T4. Overall, the microbial composition in the different treatments was weakly correlated with the sand's physical and chemical properties. In conclusion, therefore, red beetroot can be grown in an integrated vegeculture-aquaponics system in water salinities not exceeding 7.5 dSm−1.