Ecology of soil bacterial active community under TWW irrigation in an Olive orchard.

Soil bacterial community function has major roles in providing ecological services for agricultural operations. However, some management practices including irrigation with treated wastewater (TWW) may change the bacterial community composition, active members and their activity levels. The active community and the total community, based on the relative abundance of rRNA and rRNA gene sequences, under TWW irrigation of an Olive orchard soil was explored. Results showed that high quality TWW compared to conventional fresh water (FW) irrigation had little effect on the total community composition but a measurable effect on the active fraction of the soil bacterial community. Furthermore, activity levels of selected OTUs revealed annual, seasonal and irrigation type dependent fluctuations. Amongst the active members of the soil ammonia oxidizing bacteria (AOB) were found to be significantly affected by irrigation type. In-depth analysis of AOB communities in soil, using amoA gene distribution, showed that community composition and activity rate are significantly affected by TWW irrigation. Nitrosomanas nitrosa related OTU’s abundance was shown to be highly promoted by TWW irrigation in place of the dominant Nitosospira groups. The results illustrate that TWW irrigation may be sustainable in regard to its effect on the general community but to still significantly influence specific groups such as the AOB community.