Water table fluctuations generate temporally and spatially dynamic physicochemical conditions that drive biogeochemical hot spots and hot moments in the vadose zone. However, their role in the cycling of soil C remains poorly known. Here, we present results from unvegetated column experiments filled with 45 cm of artificial soil containing 10% humus, and inoculated with a natural microbial extract. In one series of three replicate columns, five cycles, each consisting of a 4‐wk drainage followed by a 4‐wk imbibition period, were imposed, whereas in a second series, the water table remained static. Depth‐resolved O₂ concentration profiles and headspace CO₂ effluxes were markedly different between the two regimes. In the fluctuating regime, drainage periods yielded 2.5 times greater CO₂ effluxes than imbibition periods. At the end of the experiment, the fluctuating water table columns exhibited a distinct zone of organic C (OC) depletion in the depth interval of 8–20 cm that was not observed under the static regime. Although this zone showed elevated levels of adenosine triphosphate (ATP), the microbial biomass was actually lower than at the corresponding depth interval of the static regime. A vertically stratified microbial community established in all columns that depended on oxygenation with depth. The 16S ribosomal RNA (rRNA) gene analyses showed a slightly higher diversity in the soil exposed to moisture fluctuations, but there was no clear difference in major taxa and microbial community composition between treatments. These results thus suggest that the localized enhancement of OC degradation induced by the water table fluctuations was driven by a more active, rather than a more abundant or compositionally very different, microbial community.

中文翻译：

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循环排水和吸水作用下人工土壤中的碳转化和微生物活性

地下水位波动会产生时空动态的物理化学条件，从而驱动渗流带中的生物地球化学热点和热时刻。但是，它们在土壤C循环中的作用仍然知之甚少。在这里，我们介绍了无植被的柱状实验的结果，该实验填充了45 cm含10％腐殖质的人造土壤，并接种了天然微生物提取物。在三个重复列的一个系列中，进行了五个循环，每个循环由一个4周的排水和一个4周的吸收期组成，而在第二个系列中，地下水位保持不变。两种方案之间，深度分辨的O ₂浓度分布和顶空CO ₂流出量显着不同。在波动的情况下，排水期产生的二氧化碳多2.5倍₂流出比吸收期大。在实验结束时，波动的地下水位柱在8-20厘米的深度范围内表现出一个明显的有机碳（OC）损耗区，这在静态条件下没有观察到。尽管该区域显示出高水平的三磷酸腺苷（ATP），但微生物生物量实际上低于静态方案中相应的深度间隔。在所有色谱柱中建立了垂直分层的微生物群落，该群落取决于深度的氧合。16S核糖体RNA（rRNA）基因分析显示，暴露于水分波动的土壤中的多样性略高，但处理之间主要分类单元和微生物群落组成没有明显差异。