Variations in soil and plant-microbiome composition with different quality irrigation waters and biochar supplementation

To reduce water scarcity in China, the use of reclaimed water or anaerobically treated piggery wastewater, either alone or coupled with biochar supplementation, is attracting increasing attention. However, little information is available regarding their effects on the soil and plant microbiomes receiving irrigation. The objective of this study was to evaluate different water quality irrigation (distilled water, reclaimed water, and piggery wastewater), biochar supplementation, and their interactions on the microbiomes of rhizosphere and bulk soil, and the root endosphere of maize using high-throughput 16S rRNA amplicon sequencing. The experiments were conducted in greenhouse rhizoboxes. The microbiome functional potentials were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). After a 60-day cultivation period, the bacterial communities and potential functions of rhizosphere, bulk soil, and root endosphere displayed distinct differences between irrigation water sources. Irrigation water quality and biochar supplementation influenced bacterial diversity in rhizosphere soil, and bacterial composition was more sensitive to irrigation water quality than to biochar supplementation in soil and root samples. Reclaimed water and piggery wastewater irrigation decreased the abundance of putative plant growth-promoting rhizobacteria (PGPR) and increased the abundance of known pathogenic bacteria. Biochar supplementation elicited the same behaviour. Mantel tests indicated that soil pH and available P exerted strong influences on the structure of the bacterial community in rhizosphere and bulk soil, but total N significantly influenced the bacterial community structure within the root. The current study implies the potential ecological effects (e.g. PGPR and pathogenic bacteria) of the irrigation with different quality water should be considered with biochar supplementation.