Phytotoxic effects of treated wastewater used for irrigation on root hydraulic conductivity and plant growth of maize seedlings (Zea mays L. PR 32w86)

Maize seedlings (Zea mays L. PR 32w86) were grown hydroponically in a nutrient solution mixed with treated wastewater (TWW) or with dialyzed treated wastewater (DTWW) obtained after the dialysis process with a cutoff at 6000–8000 Da. Within 70 min of exposure, pressurized water flow through the excised roots was reduced massively by 46% (for primary TWW, after physical treatment) and 22% (for secondary TWW, after biological treatment). In contrast, with primary and secondary DTWW, it was only slightly decreased by 22%. On the other hand, cell wall pore sizes of these roots were little reduced: by (14–27%) for primary and secondary TWW and (6–9%) for primary and secondary DTWW. Primary and secondary effluents after either TWW or DTWW affected root elongation severely by (58–76%), while reduced leaf growth rate by (26–70%) and transpiration by (14–64%). The fresh and dry plant’s weight in soil growth was also significantly affected but not with secondary DTWW. These results appeared simultaneously to involve phytotoxic and physical-clogging consequences. First, the inhibition in hydraulic conductivity through live roots (i.e., phytotoxic, and physical effects) after exposure to secondary DTWW was 22%, while through killed roots accepted after hot alcohol disruption of cell membranes (i.e., physical effects only) was only by 14%. Second, although DTWW affected root elongation severely by 58%, cell wall pore sizes of the same roots were little reduced by 6%. We conclude that large molecular weight fraction, which remained after the dialysis process, may have produced physical and phytotoxic effects on root water permeability and plant growth.