RHIZOSPHERE MICROBIOME RESPONSE TO TREATED WASTEWATER IRRIGATION

Treated Waste Water (TWW) irrigation is becoming a major and essential component of agricultural practice in increasing parts of the world. Wastewater supplies a year- round reliable source of nutrient rich water, thus turning the waste product into a valuable resource. Israel reuse more than 70% of its domestic effluent, the highest rate worldwide. Despite the increase in TWW quality, TWW irrigation may still result in unexplained undesirable effects on crops. This may be attributed, among others, to TWW effects on the plant microbiome. The rhizosphere, the zone of interaction between plant root, soil and water, encounter the TWW effects. The effects of TWW irrigation on rhizosphere microbiome structure and function have not been assessed before. Here, the effects of TWW were examined on rhizosphere and root surface (rhizoplane) microbial community composition in tomato and lettuce plants grown in two different soil types.

Rhizoplane bacterial communities were affected by both TWW irrigation and by the host plant. The effect of irrigation type and host exceeded that of soil type. In tomato roots, TWW irrigation resulted in an increase in relative abundance of Gammaproteobacteria, while in lettuce, an increase in Cytophagia was observed. In the rhizosphere, bacterial communities were mainly determined by the soil type, but the TWW irrigation also caused a shift in the bacterial community.

As the roots and their microbiome are exposed to the same environmental condition, it is hypothesized that understanding the forces that determine soil and rhizosphere microbiome response to irrigation type will shed light on natural processes in the soil and rhizosphere, and contribute to our understanding of the specific impact of TWW in these niches.