Phytotoxic effects of treated wastewater used for agricultural irrigation on root hydraulic conductivity and plant growth

Laboratory experiments on hydroponic growth conditions of maize seedlings (Zea mays L) were conducted to determine the effects of treated wastewater (TWW) on the water transport characteristics. Pressurized water flow through the excised primary roots was reduced by 25%-52%, within 90 min of exposure to TWW. Similar results were received after fractionation of TWW through dialysis tube (with a cut-off at 6000-8000 Da) i.e., dialyzed treated wastewater (DTWW), was tested. The root flow reductions appeared simultaneously to involve phytotoxic and physical clogging impacts. First, the inhibition in hydraulic conductivity through live roots (phytotoxic and physical effects) after exposure to secondary DTWW was by 22%, while through killed roots accepted after hot alcohol disruption of cell membranes (physical effects only); was only by 14%. Second, although DTWW affected root elongation severely by 58%, cell-wall pore sizes of same roots were little reduced by 6%. Additionally, the exposure to TWW or DTWW caused inhibition of both leaf growth rate by (26%-70%) and transpiration by (14%-64%). We conclude that large molecules, such as polypeptides, remained after the dialysis process, may have produced hormone-like activity that affected root water permeability. This finding can be applied to develop guidelines for neutralizing phytotoxic effects of TWW.