Nitrate application induced a lower yield loss in rice under progressive drought stress

Rice plants were subjected to nitrate application and water disruption-induced drought treatments in a screen-house using pot culture, the urea application and flood treatments were used as controls. Nitrate (Ca(NO3)(2)) application significantly increased the ratio of NO3--N to NH4+-N in the soil under both drought and flood treatments. Compared with urea application under flood treatment, both nitrate application and drought treatments caused yield losses. Under drought treatment, the yield loss of rice plant for nitrate application was 28.4% lower than that for urea application. The aboveground plant was smaller and more compact under nitrate application. Although nitrate application did not increase water uptake rate and xylem sap rate of the rice plant, nitrate application significantly stimulated the root growth of rice plant compared with urea application, especially under drought treatment, as indicated by higher root cap ratio, root biomass, root volume, root length, and density of lateral roots. Finally, the soil water potential decreased slower for nitrate application compared with urea application under drought treatment. The leaf water potential was higher for nitrate application compared with urea application under drought treatment. Our results indicated that rice plant developed a series of phenotypic adaptations to nitrate application and progressive drought, such as smaller and more compact aboveground plant, a less active but larger root system. These phenotypic adaptations made rice plant suffer less from the progressive drought stress resulting in a lower yield loss.