Appropriate partial water stress improving maize root absorbing capacity

Abstract: Partial root-zone irrigation can stimulate the compensation effect of root water uptake at the irrigated zone. Plants can compensate for water stress in one part of the root zone by taking up water from other parts of the root zone where water is available. This study aimed to identify the dynamics and influencing factors of the compensation effect of maize roots (Zea mays L. hybrid cv. Aoyu No. 3007) under partial root zone irrigation. With the split-root technology, we conducted a hydroponic experiment to analyze the root zone water stress that was simulated by the osmotic potential of a nutrient solution (PEG-6000). There were 3 water stress levels, -0.2 (mild water stress), -0.4, -0.6 MPa (moderate water stress), and a control treatment (control, both sides of the root zone supplied with sufficient water). The root growth and hydraulic conductance of each root zone were measured at 0, 0.25, 0.5, 1, 3, 5, 7 and 9 d after the experiment started. Within 0.25 d after the experiment start, the total hydraulic conductance and the hydraulic conductance per root length between the two root zones in all three treatments and control were not significantly different (P>0.05) if the water stress was less than -0.6 MPa. When the partial water stress lasted more than 0.25 d, the total hydraulic conductance and the hydraulic conductance per root length in stressed root zone were lower (P<0.05) than that in the non-stressed root zone. Compared with non-stressed root zone, the reduction rate of root hydraulic conductance in the stressed root zone was significantly (P<0.05) increased with the increase in partial water stress degree and duration. At five days, compared to the root hydraulic conductance per root length in the non-stressed root zone, the corresponding value in the stressed root zone for the treatments -0.2, -0.4 and -0.6 MPa decreased by 32.70%, 49.90% and 50.97%, respectively. Within 0.25 d after the experiment start, for the treatment -0.4 and -0.6 MPa, the total hydraulic conductance in the stressed root zone reduced by 20% and 30% compare with the treatment -0.2 MPa. Twelve hours after the experiment start, the hydraulic conductance per root length in the non-stressed root zone for the treatment -0.2 MPa increased by 10.11% compared to control, and recovered to control level after 1 d. On the ninth day, the hydraulic conductance per root length in the non-stress root zone for the treatment -0.4 MPa (25.08×10-11 m2/(MPa·s)) was significantly greater (P<0.05) than that for control, indicating this treatment had an obvious compensation effect on root water uptake. However, the corresponding value for the treatment -0.6 MPa reduced by 19.05%-40.11% after 0.5 d, which recovered to the level of control after 5 d. The results indicated that the compensation effect of root water uptake in the non-stress zone can be effectively stimulated. The compensation effect started to occur at 0.5 d after the experiment start and was affected by the degree and duration of the water stress. -0.4 MPa was the threshold of partial root zone water stress for effectively stimulating compensatory effect of root water absorption in non-stressed root zone.