Effects of light quality and intensity on nitrogen oxide gas emissions of rice phyllosphere and rhizosphere at flowering and seed setting stage

Abstract: In order to clarify the contribution of rice plants to nitrogen oxides gases (NOGs) emissions, such as N2O and NOx (NO and NO2), and understand the control mechanism of light quality and intensity, the NOGs emissions from rice phyllosphere and rhizosphere and their relationship with light quality and intensity were investigated at the flowering and seed setting stage in a liquid culture medium system. Under controlled nitrogen (N) and controlled light conditions in a light-water incubator with the separation of the inner chamber and outer chamber, the experimentation strictly separated and sealed the phyllosphere in the inner chamber and the roots in the outer chamber without harm occurring on the rice plants. For different weak light qualities (yellow, green, white, red and blue lights) and intensities (dark, 0; weak, 4 000 lx; moderate, 6 000 lx; strong, 8 000 lx), using double-chamber method, a simultaneous leaf and root determination was designed to measure the source of NOGs emissions. N2O concentration of air samples was analyzed by the gas chromatography within 10 h (from 8:00 to 18:00), while NOx (NO and NO2) gas was measured by the 42i type NO-NO2-NOx gas analyzer simultaneously. The results showed that: 1) Under a constant nitrogen nutrient (concentration of N was 90 mg/L, NH4NO3-N), when rice seedlings were treated with moderate (6 000 lx) and strong light (8 000 lx), the average rates of N2O and NO emission from rice phyllosphere were 27.08, 29.15 µg/(pot∙h) and 2.25, 0.94 µg/(pot∙h), accounting for 57.38%, 54.19% and 76.79%, 51.93% of the total N2O and NO evaporation loss for the whole rice plant, respectively. More than 90% of NOGs released from rice phyllosphere and rhizosphere was N2O, but no evident NO2 emission was detected under the same condition. 2) Under a constant light intensity (1 600 lx), N2O emission of rice phyllosphere in yellow, green, white, red and blue lights was 2.16, 13.40, 1.07, 3.82 and 7.08 µg/(pot∙h), respectively. N2O emission of rice phyllosphere and NO release of rice rhizosphere could be inhibited by red and blue light compared with the results for green light (P<0.05), while NO emissions of rice phyllosphere and rhizosphere were inhibited by blue light synchronously. Nevertheless, no evident NO2 emission of rice phyllosphere and rhizosphere was detected, and N2O emission of rice rhizosphere could be promoted by red and blue light synchronously under the same condition. 3) Within the range of 0-8000 lx, N2O emission of phyllosphere and rhizosphere and NO release of rhizosphere could be promoted by the increase of light intensity, but NO emission from rice phyllosphere was inhibited significantly by strong light (8 000 lx) illumination. 4) There was a very significant positive linear regression relationship between N2O emission of rice phyllosphere and N2O emission of rice rhizosphere (r=0.776, R2=0.587, P<0.01). Therefore, N2O emission of rice phyllosphere could be controlled by N2O release of rice rhizosphere, and the impacts of different light quality and intensity on N2O emissions of rhizosphere would further affect N2O emissions of phyllosphere. But there was not the same correlation of NO emission between rice phyllosphere and rhizosphere. In summary, by increasing the red and blue light proportions and synchronously regulating the light intensity according to nitrogen application rate, NOGs emissions of rice phyllosphere and rhizosphere can be inhibited effectively at the flowering and seed setting stage. This work clarify the contribution of rice plant to NOGs emissions and provide a scientific basis for revealing how light-control technology affects paddy NOGs emissions at the flowering and seed setting stage.