East Rice-wheat Rotation Ecosystem Xo_x Emissions

Based on static chamber techniques, measurements of NOx emission from a wheat-rice rotation ecosystem in southeast China showed that NOx emission had an obvious seasonal variability. About 85 percent of NO emission occurred during the period of a wheat growth, however, only about 15 percent during the period of rice growth. The majority of NO2 uptake occurred during the period of relatively weak plant activity or of no plant activity.There was a typical day-peak pattern of diurnal variation in NO emission during period of wheat growth. The maximum value in soil NO emission occurred between the hours of 3 p.m. and 6 p.m., which obviously lagged behind the peak soil temperature and air temperature. The regular diurnal variation pattern of NO2 uptake had not been found.During period of wheat growth, the daily emission of NO did not correlate with the soil temperature, but negatively depended upon soil moisture. With the respect to the suitable soil temperature of period of rice growth, the daily emission of NO ascribed to soil moisture. Obviously increasing NO emission has not been observed after application of N fertilization during the whole period of wheat-rice rotation. The correlation between daily uptake of NO2 and soil temperature indirectly embodied the influence of plant growth on the uptake of NO2.An elevation of atmospheric CO2 concentration reduced the emission of NO and the uptake of NO2 during the period of wheat growth and increased the emission of NO and the uptake of NO2 during the period of rice growth, which was likely due to the stimulated plant growth.