ABSTRACT The stability of black soil carbon in the deep layers of Japanese volcanic ash soil (i.e., buried A horizons) is often explained by its unique chemical (molecular structure) and physical (associated with short-range-order minerals) recalcitrance. However, the stability of black soil C in buried A horizons may be changed by labile C supply for soil microbes. Here, we hypothesized that the mineralization of black soil C in buried A horizons of Japanese volcanic ash soil could be easily accelerated by a supply of labile C (i.e., a priming effect; PE). To test our hypothesis, we investigated the direction and magnitude of the PE with a buried A horizon in Japan using 13C-labeled glucose (2.188 atom %) in a short-term (21 days) incubation study. We also investigated the effect of mineral nitrogen (N), which could contribute to microbial activity in this incubation study. We found that a positive PE occurred by glucose supply with (182%) or without (181%) mineral N input over the 21-day incubation, and its values were very similar to the PE ratios previously reported in other deep soils. The estimated mean residence time (MRT) of black soil C considering PE was clearly accelerated by glucose supply, regardless of mineral N input, compared with the initial soil MRT. These results strongly support our hypothesis that the mineralization rate of black soil C in buried A horizons is easily accelerated by a labile C supply, and it also demonstrates important implications for the effects of global warming on buried A horizons (e.g., increased root exudation, fine root biomass supply, and N deposition) in Japanese volcanic ash soils.

中文翻译：

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日本火山灰土壤深层黑土碳的矿化速度可能会因碳供应不稳定而容易加速

摘要 日本火山灰土壤深层（即埋藏的 A 层）中黑土碳的稳定性通常可以用其独特的化学（分子结构）和物理（与短程有序矿物相关）的顽固性来解释。然而，土壤微生物的不稳定碳供应可能会改变埋藏 A 层中黑土碳的稳定性。在这里，我们假设日本火山灰土壤埋藏 A 层中黑土 C 的矿化可以很容易地通过供应不稳定的 C（即启动效应；PE）而加速。为了验证我们的假设，我们在短期（21 天）孵育研究中使用 13C 标记的葡萄糖（2.188 原子％）研究了日本埋藏 A 层的 PE 的方向和幅度。我们还研究了矿物氮 (N) 的影响，这可能有助于该孵化研究中的微生物活动。我们发现，在 21 天的孵化过程中，葡萄糖供应（182%）或没有（181%）矿物质氮输入会产生正 PE，其值与先前在其他深层土壤中报告的 PE 比率非常相似。与初始土壤 MRT 相比，无论矿物质 N 输入如何，考虑到 PE 的黑土 C 的估计平均停留时间 (MRT) 明显被葡萄糖供应加速。这些结果有力地支持了我们的假设，即埋藏 A 层中黑土 C 的矿化速率很容易被不稳定的 C 供应加速，并且它还证明了全球变暖对埋藏 A 层的影响的重要意义（例如，根系分泌物增加，日本火山灰土壤中细根生物量供应和氮沉积）。