Release And Distribution Of Exogenous Carbon And Nitrogen Derived From Rice Straw In Paddy Soil

The climate in Northeast China is very cold,so that the paddy fields therein have a long fallow period when the soil is frozen for most of the time.Rice is quite short in life cycle and calls for high soil temperature and seasonal flooding for healthy growth.The practice of rice straw returning is quite popular,but little is known about how the exogenous rice straw is decomposed and how carbon?C?and nitrogen?N?in the decomposing rice straw is released and distribution during the fallow season and the rice-growing period as affected by hydrothermal condition in Northeast China.In this study,an outdoor incubation experiment was carried out using dual-isotope-labeled(¹³C and ¹⁵N)rice root,stem and leaf for tracing of the elements with the stable isotope mass spectrum analysis technique,to characterize dynamics of the decomposition rate of the incorporated rice root,stem and leaf and the release rate and distribution rate of C and N from the decomposing rice root,stem and leaf in the paddy soil.Isotope-labeled rice root,stem and leaf were added to the paddy soil in autumn.In this experiment,the outdoor culture experiment was simulated,and there were three treatments:CK?without root,stem and leaf?,S1?labeled root+unlabeled stem and leaf?and S2?unlabeled root+labeled stem and leaf?;S1 and S2 treatments add the same amount of exogenous carbon,root?0.2%?:stem and leaf?1%?=1:5.The incubation experiment time was 1 years,simulation of the soil temperature of paddy soil was the external natural ambient temperature.The soil moisture was 80%WFPS?WFPS was the soil water-filled pore water content?in rice-fallow season?November to May?and 2cm flooded layer in the rice-growing season?June to October?.The main conclusions are as follows:?1?Decomposition rates of the straw in treatment S1?labeled root+unlabeled stem and leaf?and treatment S2?unlabeled root+labeled stem and leaf?were determined to be 30.20%and 34.50%,C release rates to be 30.90%and 38.20%,and N release rate to be 7.40%and35.0%,respectively,at the end of the fallow period?November to May?.One year after the amendment,decomposition rates of the straw reached 66.50%and 66.60%,C release rates did63.70%and 65.80%,and N release rate 28.60%and 51.10%in treatment S1 and S2,respectively.The N release rate of root was significantly lower than that of stem and leaf?P<0.05?.Rice straw C is more easily decomposed and released in soil,and rice root N is more difficult to decompose and release than stem and leaf N.?2?One year after the amendment,rice root,stem and leaf were added to paddy soil,C distribution rates of rice root,stem and leaf to soil wre 11.50%and 12.70%,and N distribution rates to be 16.90%and 27.70%,respectively.The C and N distribution rates of stem and leaf to soil were significantly higher than that of root.N released of rice root,stems and leaf are more easily retained in soil than C released of rice root,stems and leaf,N released of root is more easily preserved in soil.?3?One year after the amendment,rice root,stem and leaf were added to paddy soil,the increase rates of exogenous C derived from rice root,stem and leaf to soil organic C were 0.34%and 2.02%,respectively.The increase rates of exogenous N derived from rice root,stem and leaf to soil total N were 0.02%and 0.13%,respectively..Exogenous C and N derived from root,stem and leaf were increased the content of soil organic C and total N pool.?4?One year after the amendment,rice straw?root:stem and leaf=1:5?was added to paddy soil,the addition of rice straw promoted a priming effect on the mineralization of native soil organic C and total N,The priming effect of native soil organic C and total N peak at108.20%and 155.20%,respectively,after second month of incubation;it then decreased to35.40%and 17.80%respectively,by the end of one year.Generally,the addition of rice straw had a positive priming effect on the mineralization of soil organic C and total N.Under the conditions of this experiment,one year after the amendment of rice root,stem and leaf into the paddy soil,the decomposition rates of rice roots,stem and leaf all reached about 65%.The release of C derived from the rice root,stem and leaf varied synchronously with the decomposition of the materials in rate,but N release is relatively slow.The N release rate of rice root and C distribution rate of rice root to soil were significantly lower than those of stem and leaf.The N preservation rate of rice root in soil was significantly higher than that of rice stem and leaf.Exogenous C and N of rice straw increased the content of soil organic C and total N pool,but the addition of rice straw promoted a positive priming effect on the mineralization of native soil organic C and total N.