Functional relationships between aboveground and belowground spinach (Spinacia oleracea L., cv. Racoon) microbiomes impacted by salinity and drought

Authors: Ibekwe, Abasiofiok - Mark; ORS, SELDA - Ataturk University; Ferreira, Jorge; Liu, Xuan; Suarez, Donald; MA, JINCAI - Jilin University; GHASEMIMIANAEI, ALALEH - University Of Wisconsin; YANG, CHING-HONG - University Of Wisconsin

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2020
Publication Date: 2/8/2020
Citation: Ibekwe, A.M., Ors, S., Ferreira, J.F., Liu, X., Suarez, D.L., Ma, J., Ghasemimianaei, A., Yang, C. 2020. Functional relationships between aboveground and belowground spinach (Spinacia oleracea L., cv. Racoon) microbiomes impacted by salinity and drought. Science of the Total Environment. 717. https://doi.org/10.1016/j.scitotenv.2020.137207.
DOI: https://doi.org/10.1016/j.scitotenv.2020.137207

Interpretive Summary: The southwestern United States and other semi-arid regions of the world are severely impacted by saline soils. This problem affects plant development differently especially when reclaimed wastewater or other brackish waters are practical alternatives for freshwater irrigation. This study was conducted to examine the influence of salinity and drought on soil microbial community composition and their functional relationships based on new sequencing technology. Our results indicate that the effect of salinity was more severe on the rhizosphere bacterial population than the soil bacterial composition. Furthermore, the most abundant functional genes were found in the rhizosphere. The results of this research will be used by water quality managers from different water districts, researchers, International Water Management Institute, EPA, and other local agencies that are involved in irrigation management in the southwestern United States and other semi-arid regions of the world.

Technical Abstract: Salinity is a major problem facing agriculture in arid and semiarid regions of the world. This problem may vary among seasons affecting both above- and belowground plant microbiomes. However, very few studies have been conducted to examine the influence of salinity and drought on microbiomes and on their functional relationships. The objective for the study was to examine the effects of salinity and drought on above- and belowground spinach microbiomes and evaluate seasonal changes in their bacterial community composition and diversity. Furthermore, potential consequences for community functioning were assessed based on 16S V4 rRNA gene profiles by indirectly inferring the abundance of functional genes based on results obtained with Piphillin. The experiment was repeated three times from early fall to late spring in sand tanks planted with spinach (Spinacia oleracea L., cv. Racoon) grown with saline water of different concentrations and provided at different amounts. Proteobacteria, Cyanobacteria, and Bacteroidetes accounted for 77.1% of taxa detected in the rhizosphere; Proteobacteria, Bacteroidetes, and Actinobacteria accounted for 55.1% of taxa detected in soil, while Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria accounted for 55.35% of taxa detected in the phyllosphere. Salinity significantly affected root microbiome beta-diversity according to weighted abundances (p = 0.032) but had no significant effect on the relative abundances of microbial taxa (p = 0.568). Pathways and functional genes analysis of soil, rhizosphere, and phyllosphere showed that the most abundant functional genes were mapped to membrane transport, DNA repair and recombination, signal transduction, purine metabolism, translation-related protein processing, oxidative phosphorylation, bacterial motility protein secretion, and membrane receptor proteins. Monoterpenoid biosynthesis was the most significantly enriched pathway in rhizosphere samples when compared to the soil samples. Overall, the predictive abundances indicate that, functionally, the rhizosphere bacteria had the highest gene abundances and that salinity and drought affected the above- and belowground microbiomes differently.