Effects of water and nitrogen forms on growth and xylem sap of rice seedlings

To study the effects of different water and nitrogen supply on the growth and xylem sap conditions on rice seedlings, experiments were designed under two water stress conditions, non-water stress and assimilated 50 g/L PEG water stress . Different nitrogen treatments were also designed by using various combination rate of ammonium and nitrate, with NH4+-N/NO3--N ratio of 9/1, 5/5 and 1/9. Total biomass, root morphological index, root activity and the amount of xylem sap excaudate were measured. Results showed that under non-water stress conditions, NH4+-N supply increased the average diameter of rice roots and accumulation of shoot biomass, while NO3--N increased total root absorption area and biomass accumulation in roots. The highest active absorption area and the highest percentage of active absorption area were reached when samples were treated with NH4+-N/NO3--N at a ratio of 5/5. Under water stress conditions, nitrogen ratio at 5/5 was the best for rice shoot growth, while NO3--N was beneficial to both fresh and dry weight of rice and average root diameter. Total and active root absorption area also increased with the increase of NO3--N. In non-water stress treatments, daytime water consumption dropped with the decreased ratio of NH4+-N/NO3--N. Water stress treatment significantly reduced the water uptake of rice. The amount of xylem sap was negatively influenced by water stress treatments. Highest amount of root xylem sap was found when seedlings were treated with 5/5 NH4+-N/NO3--N without water stress, and with 9/1 NH4+-N/NO3--N under water stress conditions.