Phytotoxic Effects of Treated Wastewater Used for Agricultural Irrigation On Root Hydraulic Conductivity and Plant Growth

Abstract

AimsTo determine the effects of treated wastewater (TWW) and dialyzed TWW (DTWW) through dialysis tube with a cut-off at 6000-8000 Da, on the water transport characteristics of maize seedlings (Zea mays L). MethodsLaboratory experiments were conducted to determine the effect of TWW on the hydraulic conductivity of excised roots. Moreover, the effect on transpiration, plant growth, root cell permeability and on the plant fresh and dry weight was determined. ResultsPressurized water flow through the excised primary roots was reduced by 25%-52%, within 90 min of exposure to TWW or DTWW. In hydroponics, DTWW affected root elongation severely by 58 %, while 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%). While in soil growth, the plant fresh and dry weight was also significantly affected but not with secondary DTWW. Conclusions These impacts 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%. We conclude that large molecules, such as polypeptides, remained after the dialysis process, may have produced hormone-like activity that affected root water permeability.