外源水稻根系和茎叶碳氮在稻田土壤中释放的特征

东北地区气候寒冷,稻田土壤休耕期长,多处于冻结状态;水稻生长期短,土壤温度高且季节性淹水。外源水稻秸秆碳氮在东北地区稻田土壤休耕期和水稻生长期不同水热条件下的释放特征尚不完全清楚。通过室外培养试验方法,利用双标记(~(13)C和~(15)N)水稻根系和茎叶示踪技术和稳定同位素质谱分析技术,研究水稻根系和茎叶在稻田土壤中的腐解率、有机碳(氮)释放率的动态变化特征。结果表明:水稻茎叶、根系于秋季添加稻田土壤后,经过寒冷漫长的土壤休耕期(11月至次年5月),S1(标记根系+不标记茎叶)和S2(不标记根系+标记茎叶)处理的秸秆腐解率分别达30.2%和34.5%,水稻根系和茎叶碳释放率分别达30.9%和38.2%,氮释放率分别达7.4%和35.0%。添加一年时,S1和S2处理的秸秆腐解率分别达66.5%和66.6%,水稻根系和茎叶碳释放率分别为63.7%和65.8%,氮释放率分别为28.6%和51.1%,水稻根系氮释放率显著低于水稻茎叶氮释放率(P0.05)。本试验条件下,水稻根系和茎叶添加稻田土壤1年,水稻根系和茎叶的腐解率达65%左右,其碳释放与腐解几乎同步,但氮释放相对缓慢,水稻根系氮释放速度显著低于茎叶氮释放速度,温度升高明显促进了水稻根系和茎叶的腐解及其碳氮释放。

Release of Exogenous Carbon and Nitrogen in Rice Root, Stem and Leaf in Paddy Soil

Objective] 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 during the fallow season and the rice-growing period as affected by hydrothermal condition in Northeast China.Method] 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 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.Result] Decomposition rates of the straw in Treatment S1 (labeled root + unlabeled stem and leaf) and Treatment S2 (unlabeled root + labeled stem and leaf) was determined to be 30.2% and 34.5%, C release rate to be 30.9% and 38.2%, and N release rate to be 7.4% and 35.0%, respectively, at the end of the fallow period (November to May). One year after the amendment, decomposition rate of the straw reached 66.5% and 66.6%, C release rate did 63.7% and 65.8%, and N release rate 28.6% and 51.1% in Treatment S1 and S2, respectively. The N release rate of root was significantly lower than that of stem and leaf (P< 0.05).Conclusion] 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 from the rice root, stem and leaf varied synchronously with the decomposition of the materials in rate. However, the release of N from the rice root, stem and leaf was relatively slow, especially that from the root. Higher temperature obviously promoted decomposition of and C and N release from the straw in the soil. This study is expected to be of great significance for scientific evaluation of the recycling of C and N in the incorporated rice straw in the paddy soil in Northeast China.