Regulation Of Nitrogen Form And Its Application Position On Maize Response To Water Stress Under Partial Root-zone Drying

Abstract: Alternate partial rootzone drying (A-PRD) is a new water-saving irrigation regime, and fixed partial rootzone drying (F-PRD) is common in practice. However, researches on the interactions between water supply and fertilizer application under the PRD regimes received little attention, and most of them were focused on the effects of amount and location of water and nitrogen supplied on the nitrogen absorption, environmental residual, and crop yields. Nitrogen form influences plant growth and plant resistance to water stress greatly. However, little is known about the effects of nitrogen form and its application position (Nitrogen supplied homogeneously to stressed- and non-stressed-side, or just one side with PEG or water) on plant responses to water stress under PRD conditions. To address this issue, and the possible mechanisms, photosynthesis, chlorophyll fluorescence parameters, chlorophyll content, plant growth responses, water and nutrient uptake and utilization, abscisic acid contents in different parts of the plant, xylem sap flow rate and pH, morphological characteristics and anatomic structure responses were examined in this research.The results showed that, compared with nitrogen supplied to water-stressed compartment, nitrogen supplied to the non-water-stressed compartment relatively improved photosynthetic rate, light energy usage and light conversion efficiency (Yield,ETR,qP,ETRm), plant transpiration rate, total water consumption, xylem sap flow rate, chlorophyll content, root activity, nutrient uptake and plant biomass,but reduced photorespiration rate (Rp), abscisic acid (ABA) concentration of xylem sap, nitrogen and water use efficiency of the plants. Under the conditions of nitrogen supplied to water-stressed or non-water-stressed compartment, photosynthetic rate, light energy usage and light conversion efficiency. Plant transpiration rate, total water consumption, xylem sap flow rate and plant biomass decreased at the following tendency as mixed nitrogen source, nitrate nitrogen, ammonium nitrogen. However, ammonium nutrition had a greater effect on the increment in ABA concentration, water and nitrogen use efficiency of plant compared to other nitrogen sources.Under F-PRD conditions and nitrogen added to two root compartments homogenously, at the initial stage of water stress treatment, photosynthetic rate (Pn), actual quantum yield of PSII (Yield), electronic transmission of photosynthesis (ETR) and photochemical quenching coefficient (qP) were relative higher in plants supplied with ammonium than the other nitrogen sources, resulting in a promoted plant growth induced by ammonium supply. However, at the 7th day after the water stress treatment, the Pn, Yield, ETR, qP and chlorophyll content decreased greatly in plant supplied with ammonium compared to the other nitrogen source, resulting in a stunted growth for ammonium-supplied plant. The growth of plant supplied with nitrate or mixed nitrogen source was promoted comparatively at the late stage of partial root water stress treatment. Plant supplied with mixed nitrogen could maintain relative higher water transportation rate as time of water stress prolonged comparing with NH4+-N and NO3--N supplement. However, ammonium nutrition had a greater effect on the increment in xylem sap pH and ABA concentration in different parts of plant compared to other nitrogen sources. Therefore, water use efficiency improved by ammonium supply.Under A-PRD conditions and nitrogen added to two root compartments homogenously, at the initial stage of water stress treatment, photosynthetic rate (Pn), actual quantum yield of PSII (Yield), electronic transmission of photosynthesis (ETR) and photochemical quenching coefficient (qP) were relative higher in plants supplied with ammonium than the other nitrogen sources, resulting in a promoted plant growth induced by ammonium supply. Plant growth and the physiological consequences showed a recovery and compensation mechanism during the alternation course. Plants treated with nitrate showed a greater compensation effect than ammonium during the alternation course. In particular the growth of roots was obviously promoted by nitrate. Increment of biomass of plants treated with nitrate was higher than ammonium three days after alternation. The increase tendency was also found on plants treated with mixed nitrogen. However, the photosynthesis, light energy usage and conversion efficiency decreased greatly in plants supplied with ammonium compared to the other nitrogen source, resulting in growth for ammonium-supplied plants slowing down. Under A-PRD conditions, the ABA stored in formerly stressed root half released to xylem, inducing a up to 2-2.5 fold increment in ABA content in xylem sap flow,with the sap flow rate decreased.Ammonium nutrition had a greater effect on the increase in xylem sap pH and ABA content, compared to other nitrogen sources. water use efficiency improved by ammonium supply.