δ^(13)C法研究砂姜黑土添加秸秆后团聚体有机碳变化规律

Change law of organic carbon in lime concretion black soil aggregates with application of straw by δ^(13)C method

为研究水稻秸秆添加对砂姜黑土水稳性团聚体分布及稳定性的影响,探索水稻秸秆腐解过程中外源新碳及原有机碳在不同粒级团聚体中的分配规律,该文通过室内模拟试验,运用δ^(13)C示踪方法,将稳定同位素碳(δ^(13)C)标记的水稻秸秆添加入砂姜黑土,利用湿筛法得到不同培养时期不同粒级的土壤水稳性团聚体,测定不同时期各粒级土壤外源新碳及原有机碳含量。结果表明:未添加水稻秸秆的砂姜黑土(对照组),水稳性微团聚体(<250μm)占主体,团聚体有机碳含量低。与对照相比,添加水稻秸秆(试验组)显著促进了>2000、2000~250μm粒级水稳性大团聚体的团聚(P<0.05);培养到120 d时,>2000、2000~250μm水稳性团聚体比对照组分别增加了265.5%、16.0%,促使水稳性大团聚体(>250μm)占主体,显著提高了砂姜黑土水稳性团聚体的平均重量直径(mean weight diameter,MWD)、几何平均直径(geometric mean diameter,GMD)、水稳性大团聚体含量(R0.25),降低了分形维数(D)值(P<0.05),土壤结构稳定性明显得到改善。试验组各粒级团聚体有机碳含量显著增加,培养到15 d时,>2000、2000~250、>250~53、<53μm粒级团聚体有机碳分别比对照组增加了21.4%、25.4%、34.7%、50.0%,其中微团聚体有机碳增加幅度大于大团聚体的增加幅度。MWD、GMD、R0.25与2000~250、>250~53μm粒级团聚体有机碳呈极显著正相关关系(P<0.01),与>2000μm粒级团聚体有机碳呈显著正相关关系(P<0.05)、与<53μm粒级团聚体有机碳关系不显著。不同粒级团聚体的δ^(13)C值明显增加,动态变化较大,表明外源新碳周转速率较快。外源新碳主要分配在>250~53、<53μm粒级微团聚体中,分配比例分别为38%、28%,外源新碳的分解速率明显快于原有机碳。研究得出添加水稻秸秆有利于增加砂姜黑土的团聚体稳定性,提高土壤及不同粒级团聚体的有机碳含量,提升土壤碳水平,改善了土壤结构,这为淮北地区土壤质量提升及有机碳循环提供了理论依据。

Straw application is an essential measure for improving soil organic carbon （SOC） content, promoting soil aggregate formation and improving soil structure. In order to study the effects of application of rice straw with stable carbon isotope （δ13C） on distribution and stability of water-stable aggregates of lime concretion black soil, and explore the dynamic variation and distribution of native soil organic carbon and fresh carbon in soil water-stable aggregates during straw decomposition, the rice straw spiked with the natural abundance of 13C was incorporated with the lime concretion black soil. This experiment was conducted in a constant-temperature incubator indoor for 4 month, which used isotope tracer technique of the natural abundance of 13C. The experiment included 2 treatments： CK （no straw） and Str （added with 1% straw）; all samples were separated into 4 aggregate-size classes （〉2000, 250-2000, 53-〉250, 〈53μm） by wet sieving in the different incubation period, while organic carbon in bulk soil and soil aggregates in different size fraction were determined. The results showed that the content ofmicroaggregates （〈250μm） in lime concretion black soil without rice straw was the highest, and the concentrations of organic carbon in various aggregates were lower than that with 1% straw. Compared with the control, the application of rice straw in lime concretion black soil not only significantly promoted the formation of 〉2000 and 250-2000 μm soil water-stable macroaggregates （P〈0.05）, but also increased the mean weight diameter （MWD）, geometric mean diameter （GMD） and macroaggregate content （R0.25） of water-table aggregates. Also, the value of fractal dimension in straw treatments was lower than the control. Specifically, MWD, GMD and R0.25 value of aggregates of the straw treatments increased by 21.5%, 34.3% and 21.3% compared with the CK, respectively. And the fractal dimension value of straw treatments decreased by 2% compared with that of CK. After 120 days of incubation, 〉2000 and 250-2000μm soil water-stable macroaggregates increased by 265.5% and 16.0% respectively, while the content of macroaggregates （〉250μm） became the highest, accounting for 63.28%. Consequently, application of rice straw was beneficial to the improvement of soil structure. The concentrations of organic carbon in different levels of aggregates were significantly （P〈0.05） increased after additions of rice straw and the organic carbon contents in 〉2000, 250-2000, 53-〉250, and 〈53μm aggregates were increased by 21.4%, 25.4%, 34.7%, and 50.0% compared with the control after 15 days of incubation. There is a most significant relationship between the GMD, MWD, Ro.25 value and the concentrations of organic carbon in 250-2000 and 53-〉250μm aggregates （P〈0.01）, and a significant relationship between the GMD, MWD, R025 value and the concentrations of organic carbon of 〉2000 μm aggregates （P〈0.05）. The dynamic variation of δ13C in soil water-stable aggregates was significant and the content of δ13C in soil water-stable aggregates improved significantly （P〈0.05）, which showed that the turnover rate of fresh carbon was faster. The fresh carbon supplied by rice straw was mainly in the 53-〉250 and 〈53μm fraction of soil aggregates, making up 38% and 28% of the total, respectively. The result shows that the addition of rice straw can improve soil structure, and increase soil organic carbon content inall sizes of aggregates, which provide theory basis for soil quality improvement and organic carbon recycle in North China.