Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2016
Publication Date: 12/1/2016
Citation: Ibekwe, A.M., Ors, S., Ferreira, J.F., Liu, X., Suarez, D.L. 2016. Seasonal induced changes in spinach rhizosphere microbial community structure with varying salinity and drought. Science of the Total Environment. 579:1485-1495. doi: 10.1016/j.scitotenv.2016.11.151.
Interpretive Summary: Environmental stress is a major limitation in saline agricultural especially where high salinity from irrigation practices combined with drought may affect the selection, growth and yield of crops. This is the case in the southwestern United States and other semi-arid regions of the world where use of reclaimed waste water or other brackish waters may be a practical solution for fresh water scarcity. In this study, next generation sequencing was used to determine how the incorporation of drought into the experimental variables may provide insights into how salinity drought interaction may affect rhizosphere microbial population. Our results indicate that the effect of salinity was more severe on the rhizosphere bacterial population than the bulk soil bacterial composition. Furthermore, temporal variability differentially affected rhizosphere microbial communities irrigated with saline wastewater. Therefore, temporal variability associated with temperature differentially affected rhizosphere microbial community composition. 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 southwestern United States and other semi-arid regions of the world.
Technical Abstract: Salinity is a common problem under irrigated agriculture, especially in low rainfall and high evaporative demand areas of southwestern United States and other semi-arid regions around the world. However, studies on salinity effects on soil microbial communities are relatively few while the effects of irrigation-induced salinity on soil chemical and physical properties and plant growth are well documented. In this study, we examined the effects of salinity, temperature, and temporal variability on soil and rhizosphere microbial communities in sand tanks irrigated with prepared solutions designed to simulate saline wastewater. Three sets of experiments with spinach (Spinacia oleracea L., cv. Racoon) were conducted under saline water during different time periods (early winter, late spring, and early summer). Bacterial 16S V4 rDNA region was amplified utilizing fusion primers designed against the surrounding conserved regions using MiSeq® Illumina sequencing platform. Across the two sample types, bacteria were relatively dominant: Proteobacteria, Cyanobacteria, and Bacteroidetes accounted for 77.1% of taxa detected in the rhizosphere, while Proteobacteria, Bacteroidetes, and Actinobacteria accounted for 55.1% of taxa detected in soil. The results were analyzed using UniFrac coupled with principal coordinate analysis (PCoA) to compare diversity, abundance, community structure, and specific bacterial groups in soil and rhizosphere samples. Permutational analysis of variance (PERMANOVA) analysis showed that soil temperature (P = 0.001), rhizosphere temperature (P = 0.001), rhizosphere salinity (P = 0.032), and evapotranspiration (P = 0.002) significantly affected beta diversity of soil and rhizosphere microbial communities. Furthermore, salinity had marginal effects (P = 0.078) on soil beta diversity. However, temporal variability differentially affected rhizosphere microbial communities irrigated with saline wastewater. Therefore, microbial communities in soils impacted by saline irrigation water respond differently to irrigation water quality and season of application due to temporal effects associated with temperature.