[Effects of nitrogen form and its supply position on maize seedling growth under partial root-zone water stress]

A split root system consisting of two compartments was installed to study the effects of nitrogen form and its supply position on the growth of maize seedlings under partial root-zone water stress. Polyethylene glycol (PEG 6000) was added to the nutrient solution in one compartment to simulate partial root-zone water stress, while nitrogen was set as three forms (nitrate nitrogen, ammonium nitrogen, and their 1 : 1 mixture) and supplied to just one compartment (water-stressed or non-water-stressed compartment). Photosynthetic and other physiological indices were examined. Comparing with the nitrogen supplied to water-stressed compartment, the nitrogen supplied to non-water-stressed compartment improved the photosynthetic rate (P(n)), maximum net photosynthetic rate (P(max)), light saturation point (LSP), CO2 saturation point (CSP), chlorophyll content, root activity, nitrogen uptake, and biomass accumulation, but reduced the photorespiration rate (R(p)), CO2 compensation point (CCP), abscisic acid (ABA) concentration in xylem sap, and nitrogen- and water use efficiency of the plants. Supplying nitrate nitrogen or its mixture with ammonium nitrogen improved the P(n), P(max), LSP, CSP, nitrogen uptake, and biomass accumulation, but reduced the CCP, R(p), ABA concentration in xylem sap, and nitrogen- and water use efficiency of the plants, compared with supplying ammonium nitrogen. All the results showed that supplying same nitrogen forms to non-water-stressed compartment was more beneficial to the plant growth but disadvantageous to the plant nitrogen- and water use, compared with supplying the nitrogen forms to water-stressed compartment, and supplying nitrate nitrogen or its mixture with ammonium nitrogen promoted the plant growth but reduced the plant nitrogen- and water use, compared with supplying ammonium nitrogen.