Decomposition Of Rice Straw In Paddy Soil And Characteristics Of CO₂ And CH₄ Emission In Northeast China

Returning rice straw to the field is of great significance for soil fertility cultivation,carbon（C）cycle and greenhouse gas emission.The climate in the northeast is cold,the rice planted is one year old,and the rice growing season is short（from mid-May to mid-October every year）,the soil temperature is high,seasonal flooding.The rice-fallow season is long（from mid-to-late October to the first half of May of the next year）,the soil temperature is relatively low,the water content is relatively small,and it is mostly in a frozen state.The soil hydrothermal conditions in the rice-fallow season and the rice growing season are significantly different.However,after the rice straw is returned to the field in the rice-fallow season and the rice growing season.What are the characteristics of rice straw decomposition and the CO₂,CH₄ emission from straw C?Do not know yet.Therefore,this paper take the paddy soil in Northeast China as the research object,and use ¹³C-labeled rice straw as the test material to study the dynamic changes of rice straw decomposition,the dynamic change of C release from rice straw and the dynamic change of CO₂,CH₄ emissions after rice straw returning to the paddy soil in the rice-fallow and rice growing season through the indoor incubation experiment.The characteristics of rice straw decomposition and the CO₂,CH₄emission from straw C in paddy soil of Northeast China were determined.The indoor incubation experiment was set up the no added straw and added straw treatment,the rice-fallow season was aerobic incubation（24 weeks）and the soil temperature was set to-10℃,0°C,10°C.Soil moisture was set to 60%WFPS and 100%WFPS（WFPS is soil water-filled pore moisture content）.The subsequent rice growing season was anaerobic incubation（16 weeks）,soil temperature was set to 25°C,soil moisture was recorded as 1cm of flooding.The main conclusions from the study were as follows:（1）The decomposition rate of rice straw,the decomposition rate and emission rate of straw C were significantly affected by soil temperature and moisture in the aerobic incubation,and the effect of soil temperature was significantly greater than that of soil moisture.The decomposition rate of rice straw,the decomposition rate and the emission rate of straw C increased significantly with the increase of temperature in the aerobic incubation,and decreased with the increase of aerobic incubation temperature in the subsequent anaerobic incubation.（2）During the whole incubation（40 weeks）,at-10°C,0°C and 10°C,the decomposition rate of rice straw were 51.24%～55.23%,61.06%～62.27%and 63.29%～67.69%,respectively,the decomposition rate of straw C(¹³C)were 73.47%～76.73%,69.03%～73.23%and71.65%～75.34%respectively,the emission rate of straw C(¹³C)were 7.33%～9.63%、7.4%～8.46%和15.25%～15.73%respectively.At-10°C,The straw and straw C decomposition are mainly concentrated in the anaerobic incubation,while the straw and straw C decomposition at 0°C and 10°C are mainly concentrated in the aerobic incubation.（3）During aerobic incubation（24 weeks）,at-10°C,0°C and 10°C,the soil CO₂ emission in the added straw treatment were 2.96～3.76 times,8.77～9.61 times and 9.07～9.58 times of soil CO₂ emission in the no added straw treatment.During the anaerobic incubation（16weeks）,at-10°C,0°C and 10°C,the total soil CO₂ and CH₄ emissions in the added straw treatment were 5.28～6.03 times,3.38～3.53 times and 2.63～2.96 times of the total soil CO₂and CH₄ emissions in the no added straw treatment.During anaerobic incubation,the amount of CH₄ produced by aerobic incubation at-10°C was significantly greater than that of aerobic incubation at 0°C and 10°C.（4）The addition of rice straw has obvious priming effect on the mineralization and decomposition of the SOC.It produces a positive priming effect during the aerobic incubation,the priming effect was weakened with the increase of temperature and moisture.During the subsequent anaerobic incubation,the priming effect gradually changed from positive priming effect to negative priming effect with the increase of aerobic incubation temperature.During the whole incubation period（40 weeks）,under the conditions of aerobic incubation-10°C,0°C and 10°C,the addition of rice straw had a positive priming effect on the mineralization and decomposition of SOC,the positive priming was 0℃（163.32%～274.27%）>-10℃（121.30%～125.30%）>10℃（75.00%～79.64%）。Under the conditions of this experiment,the effect of soil temperature on the decomposition of rice straw and the decomposition and transformation of straw C was significantly greater than that of soil moisture during the aerobic incubation.The increase of soil temperature can significantly promote the decomposition of rice straw,the decomposition and CO₂,CH₄ emissions of straw C.At the same time,the addition of rice straw had positive priming effect on the mineralization and decomposition of the SOC.The positive priming effect increased first and then decreased with the increase of soil temperature.