There is increasing evidence that the accessibility of soil organic matter (SOM) to microbial decomposers is more important than chemical recalcitrance for regulating SOM stability. We show that the rapid reduction in SOM decomposition following the addition of sorptive mineral phases to soils in laboratory conditions leads to decreased accessibility of SOM to microbial decomposers due to the formation of organo-mineral complexes. We manipulated SOM accessibility in a short-term microcosm experiment by adding different proportions of a sorptive mineral material derived from an aluminium-rich allophanic soil to a constant mass of soil to determine the effects on SOM decomposition after 1, 4 and 8 days. The decrease in SOM decomposition with increasing proportion of added sorptive mineral phase occurred within 1 day and did not change further at 4 and 8 days. In a second experiment, we added three proportions of the sorptive mineral phases (0%, 15% and 50%) to three soils with different carbon (C) concentrations and measured rates of SOM decomposition, changes in water extractable C, the formation of organo-mineral complexes inferred from pyrophosphate-extractable aluminium, and the natural abundance ¹³C isotopic composition of CO₂ derived from SOM decomposition. We confirmed that the proportional decreases in SOM decomposition with increasing organo-mineral complexes and decreasing microbial access to SOM was the same for the three soils, suggesting that the effects are independent of soil C concentration and pH. We also showed that the short-term reductions in SOM accessibility led to microbial decomposition of more ¹³C enriched substrates, suggesting preferential stabilisation of plant-derived (¹³C depleted) substrates. Our study demonstrated that SOM accessibility and decomposition could be reduced rapidly and proportionally to the amount of added sorptive mineral phases resulting from increased organo-mineral interactions irrespective of the initial soil organic carbon concentration.

中文翻译：

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向土壤中添加吸附性矿物相可通过减少微生物对基质的接触来减少短期有机物分解

越来越多的证据表明，对于调节 SOM 稳定性，土壤有机质 (SOM) 对微生物分解者的可及性比化学顽固性更重要。我们表明，在实验室条件下向土壤中添加吸附性矿物相后，SOM 分解的快速减少导致由于有机矿物复合物的形成，SOM 对微生物分解剂的可及性降低。我们在短期缩影实验中控制了 SOM 的可及性，方法是将不同比例的源自富含铝的脲基质土壤的吸附性矿物材料添加到恒定质量的土壤中，以确定 1、4 和 8 天后对 SOM 分解的影响。随着添加的吸附矿物相比例的增加，SOM 分解的减少发生在 1 天内，并且在 4 和 8 天没有进一步变化。在第二个实验中，我们将三种比例的吸附矿物相（0%、15% 和 50%）添加到具有不同碳 (C) 浓度的三种土壤中，并测量了 SOM 分解速率、水可提取 C 的变化、从焦磷酸盐可萃取铝推断的有机矿物配合物及其天然丰度源自 SOM 分解的 CO _2的¹³ C 同位素组成。我们证实，随着有机矿物复合物的增加和微生物接触 SOM 的减少，SOM 分解的比例减少对于三种土壤是相同的，这表明这种影响与土壤 C 浓度和 pH 值无关。我们还表明，SOM 可及性的短期降低导致更多¹³ C 富集底物的微生物分解，表明植物来源的优先稳定化 ( ¹³C耗尽）底物。我们的研究表明，无论初始土壤有机碳浓度如何，SOM 的可及性和分解都可以迅速减少，并且与添加的吸附性矿物相的量成正比，这是由于有机矿物相互作用增加而导致的。