The effects of boron-enriched water irrigation on soil microbial community are dependent on crop species

The extreme rainfall shortage forecasted for the coming decades will compromise water availability in arid and semiarid regions around the planet. To address water scarcity in agriculture, desalinated seawater stands out as the most feasible option among the current alternative water sources. However, its high content of boron (B), among other phytotoxic elements, entails a potential risk for plant-soil sustainability. Here, we tested the response of the crop-soil system to different concentrations of B (0, 0.3, 1 and 15 mg B L-1) in the irrigation water, in an open-air pot experiment. Onion (Allium cepa L.), with a higher sensitivity to B toxicity, and tomato (Solanum lycopersicum L.) were used as model horticultural crops. Shifts in the biomass and the structure of the soil microbial community, as estimated by fatty acid analyses, due to the medium B dose (1.0 mg L-1) depended on the plant species. Indeed, the highest B dose (15 mg L-1) increased the B content in the soil, exceeding the toxic threshold and disturbing the soil nitrogen cycle. The activity, structure and biomass of the soil microbial community are the most sensitive soil properties to B accumulation in the soil and they are also negatively impacted by the large amount of B added to the soil. Moreover, the increased supply of B fostered its bio-accumulation in plant tissues. Nevertheless, the highest B dose only had harmful effects on tomato crops, con-sisting of yield reduction and foliar nutrient imbalance.