Research The Physiological And Biochemical Mechanism Of N₂O Emissions In The Soil-soybean System

N₂O is a kind of very important greenhouse gas. Its density is approximately 0.32ppm in the atmosphere at present, the annual growth rate of the gas is about 0.25%. The contribution rate of N₂O to global warming is about 6%. Its global warming potential is 310 times than that of CO₂. Also, it has damaging effects on the ozone layer and increases UV-B radiation of global surface. However, the sources and sinks of atmospheric N₂O estimated is still a lot of uncertainty,The strength estimating of certain N₂O emission source is insufficient possibly or certain important source was not found. People believed that microbial nitrification and denitrification of the soil-plant system is the sole biological source of N₂O emissions to the atmosphere, and ignored other N₂O biological emission processes.CHEN guan-xiong first reported that the plants in the normal physiological conditions can release N₂O. the important discovery provided a new research orientation to estimate the N₂O source of this biological. It provided possibility to improve the accuracy of estimating the sources and sinks of N₂O. However, the research of plant N₂O emissions focused on the influence of environmental factors, but the contribution of plant to N₂O emission from the soil-plant system in field , few reports were involved in this important issue, while some reports have showed that the contribution vary greatly, from less than 7% to 50%. This largely due to the big differences in methods used to.This experiment used the separated closed chamber method to measure the N₂O emissions from soybean and soil under field condition. It preliminary studied the contribution of soybean to N₂O emission from the soil-plant system in field applying the gas chromatography and isotope ratio mass spectrometry. the factors to affect N₂O emission are examined, such as light intensity,temperature,photosynthetic rate,transpiration rate,stomatal conductance; the relationship of nitrate reductase,nitrite reductase,nitrate content,nitrite content of N metabolism of the plant with N₂O emissions were studied; the relationship of temperature and the humidity With N₂O emissions by soil were researched; and the N₂O transmission experiment by soybeans through closed box was studied. The results showed:In order to study soybean whether transmit N₂O from soil. Soybeans were placed in pour water and the water was pumped into 2ml/L of N₂O. Experimental results showed that soybean N₂O emission in pure water and the water pumped into N₂O have no significant difference, so the soybean did not transfer N₂O in water. The N₂O consistency is very low in the soil, so soybeans do not transfer N₂O in soil.The experiment observed the contribution of soybean to N₂O emission from the soil-plant system in field applying separated closed chamber method. The results showed: during more than 50 days of the observation period, Soybean N₂O emissions in the soil-plant system had a great difference (8%-67%). Fertilize urea and does not fertilize urea treatment, the average contribution rate is 24.47%,20.13% respectively, and the contribution rate of Urea treatment was higher than not fertilize urea. Thanks to the determination of soil-plant system N₂O emission value with the closed box is not very accurate and reliable, when Calculating the soil-plant system N₂O flux, used the sum of plants and soil N₂O flux emissions. It Confirmed that the plant may be atmospheric N₂O emission sources. It may be underestimate the N₂O emission strength of terrestrial ecosystems in the past.In this experiment used closed box methods to study changes law of Soybean N₂O emissions, the results show that: during the blossoming period of plants, the soybean N₂O emissions flux is fewer and little change, and emissions fluxes sharply increase to reach a peak When the soybean maturity. The main reason to make this phenomenon was that soybean nutrition N transferred from the old leaves to cause the dramatic increase of soybean N₂O emissions flux for the soybean maturity period with the soybean plant senescence. And in the whole observation period , the N₂O emissions flux of Urea treatment was higher than not fertilize urea, So nitrogen fertilizer can increase N₂O emissions.In this experiment used closed box methods to study changes law of soil N₂O emissions flux for the continuous observation. The results showed that the N₂O emissions from the soil relatively stable, without much change in prophase. From the beginning of August 7, N₂O emissions have reached a peak and in the late soybean maturity, the flux also significant increased to form another emissions peak. This is probably due to soybean nodules rupture in the late maturity causing a large amount of fixed nitrogen into the soil.The experiment studied the relationship of nitrate reductase,nitrite reductase,nitrate content,nitrite content of N metabolism of the plant with N₂O emissions. The results showed that there was positive correlation between N₂O emission and nitrate reductase,nitrite reductase,nitrate content,nitrite content.The factors to affect N₂O emissions are examined when observed plants N₂O emissions, the results showed: light and temperature are important factors affecting N₂O emissions, and there is a positive correlation between photosynthetic rate,respiratory rate,stomatal conductance and N₂O emission from plants.The experiment examined temperature and humidity to affect N₂O emissions when Observed soil N₂O emissions, the results showed: temperature and Urea,not fertilize urea treatment had a linear relationship, related coefficient of 0. 573, 0. 5494 respectively, and no linear relationship with the naked treatment. The related coefficient Soil Moisture with Urea, not fertilize urea, naked treatment was 0. 1834,0.3559, 0.8141, the soil Moisture with naked treatment have linear relationship and had no linear relationship with the Urea, not fertilize urea treatment. The experiment observed the contribution of soybean to N₂O emission from the soil-plant system in field applying IRMS. the results showed: the contribution of soybean to N₂O emission from the soil-plant system is 56. 5%,this value is more large than GC value.