秸秆添加下黑土团聚体周转过程驱动有机碳累积

Sequestration of Soil Organic Carbon is Driven by Aggregate Turnover under Straw Addition in Mollisols

    摘要
  • 摘要:
    目的 土壤结构和土壤有机碳（SOC）动态变化是影响土壤质量的关键因子，秸秆还田下土壤团聚体周转和团聚体内有机碳累积的耦合过程不清。
    方法 利用稀土氧化物（REOs）示踪技术，区分土壤团聚体形成和破碎过程，探究不同秸秆降解时间下（6、9、12个月）秸秆种类（苜蓿秸秆、玉米秸秆）对团聚体粒径分布、平均重量直径（MWD）、团聚体周转过程以及团聚体有机碳累积的影响。
    结果 秸秆残留率随时间延长显著降低，表现为：苜蓿秸秆 > 玉米秸秆（P < 0.05）。与对照相比（未添加秸秆），苜蓿秸秆和玉米秸秆添加显著提高大团聚体（ > 0.25 mm）含量和MWD，同时，提高大团聚体的形成比例，降低破碎比例，总体表现为：玉米秸秆 > 苜蓿秸秆，并于第9个月增加效果最佳（P < 0.05）。大团聚体含量及其相对形成量分别解释MWD变异的35.9%和32.8%，表明土壤MWD主要受大团聚体变化调控。与对照相比，秸秆添加分别使土壤和团聚体有机碳含量提升了1.5% ~ 5.6%和0.6% ~ 43.9%，前期主要提升 > 0.25 mm团聚体有机碳含量，后期提升 < 0.25 mm团聚体有机碳含量（P < 0.05）。三种处理下土壤和团聚体有机碳含量均在第6个月达到最大值，随后显著降低（P < 0.05）。相比于团聚体的粒径分布，其相对变化量对团聚体有机碳变异的解释度更高（51.6% vs. 81.8%），表明团聚体周转过程主控团聚体有机碳累积。
    结论 秸秆添加通过增加大团聚体相对形成量，降低相对破碎量，促进团聚体有机碳累积。

     

    Abstract:
    Objective Soil structure and soil organic carbon (SOC) dynamics are crucial to soil quality. However, the interactions between soil structural dynamics and SOC changes remain unclear. The purpose of this study was to elucidate the coupling process of aggregate organic carbon accumulation and aggregate turnover under straw addition.
    Method Rare earth oxides (REOs) were used as tracers to track aggregate formation and breakdown pathways. Two different types of straw (alfalfa and maize straw) were added to REOs-labelled Mollisols. Soil aggregate distribution, mean weight diameter (MWD), aggregate turnover, and organic carbon content were measured after the 0th, 6th, 9th and 12th months of incubation.
    Results The results showed that the remaining mass of added straw significantly decreased with time, in which the higher content was observed with alfalfa application compared with maize straw. The content of macroaggregates (> 0.25 mm) and MWD reached the peak on the 9th month and then decreased significantly with or without straw addition. Compared with the control treatment, MWD was increased by 33.7% and 37.3% under alfalfa and maize straw treatments (P < 0.05). Straw addition significantly increased > 0.25 mm aggregates proportions and reduced < 0.25 mm aggregates contents, such effects were more considerable in maize treatment compared with alfalfa treatment (P < 0.05). The proportions and relative changes of macroaggregates explained 35.9% and 32.8% to the variation of MWD, indicating that MWD is mainly determined by macroaggregates changes. The SOC and macroaggregate SOC contents reached a maximum in all three treatments on the 6th month and then decreased significantly (P < 0.05). Compared to the control, straw addition increased carbon contents in bulk soil and aggregates by 1.5%-5.6% and 0.6%-43.9%. At the early stage of straw decomposition, the SOC content in > 0.25 mm aggregates as enhanced, while that in < 0.25 mm aggregates was accumulated afterwards (P < 0.05). Compared to aggregate distribution, the relative changes in aggregates explained the highest variation of aggregates organic carbon (51.6% vs.81.8%), suggesting that the aggregates turnover determined the sequestration of organic carbon in aggregates.
    Conclusion Straw addition increased the SOC content of aggregates by promoting the formation of macroaggregates and decreasing relative breakdown.

     

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