In contrast to what is observed in aerobic uplands, microbial biomass and the presence of electron acceptors, such as iron oxides, play a crucial role in regulating soil organic C (SOC) mineralisation in paddy soils. However, the related underlying mechanisms are still poorly explored. We conducted an anaerobic incubation study to investigate changes in CO 2 emissions from SOC and acetate ( 13 C-labeleld) in response to iron oxide (ferrihydrite and goethite) addition in chloroform-fumigated and unfumigated paddy soils. The iron oxides, as electron acceptors, increased CO 2 emissions from SOC with stronger impact under ferrihydrite than goethite addition. However, the acetate addition, as a preferable C source for reducing microbes, decreased SOC mineralisation and caused a negative priming effect. CO 2 emission from both acetate and SOC was affected by microbial biomass change. In the acetate-treated soil, goethite in the fumigated soil (i.e. high microbial biomass) increased CO 2 emissions from acetate, providing electron acceptors, and decreased CO 2 emissions from SOC. Ferrihydrite accepted electrons and adsorbed acetate, resulting in a slight decline in CO 2 emission from acetate. However, in the fumigated soil (i.e. low microbial biomass), both iron oxide additions reduced CO 2 emissions from acetate and SOC and likely the dominant role of both iron oxides shifted from being electron acceptors to being adsorbents, thus limiting acetate accessibility to microorganisms. The results suggest that microbial biomass is a key driver in shifting the effects of iron oxides on organic C mineralisation in anaerobic paddy soils.

中文翻译：

---

低、高微生物量条件下缺氧稻田有机碳矿化对氧化铁添加的响应对比

与在好氧高地观察到的情况相比，微生物生物量和电子受体（如氧化铁）的存在在调节稻田土壤有机碳 (SOC) 矿化方面起着至关重要的作用。然而，相关的潜在机制仍然缺乏探索。我们进行了一项厌氧培养研究，以研究在氯仿熏蒸和未熏蒸的稻田土壤中添加氧化铁（水铁矿和针铁矿）后 SOC 和醋酸盐（ 13 C-labeleld）的 CO 2 排放变化。作为电子受体的氧化铁增加了来自 SOC 的 CO 2 排放，在水铁矿下的影响比针铁矿添加的影响更大。然而，作为减少微生物的优选碳源，添加乙酸盐会降低 SOC 矿化并导致负面启动效应。来自醋酸盐和 SOC 的 CO 2 排放受微生物生物量变化的影响。在醋酸盐处理的土壤中，熏蒸土壤中的针铁矿（即高微生物生物量）增加了醋酸盐的 CO 2 排放，提供了电子受体，并减少了 SOC 的 CO 2 排放。水铁矿接受电子并吸附醋酸盐，导致醋酸盐的 CO 2 排放量略有下降。然而，在熏蒸土壤中（即低微生物生物量），两种氧化铁添加都减少了醋酸盐和 SOC 的 CO 2 排放，并且两种氧化铁的主要作用可能从电子受体转变为吸附剂，从而限制了微生物对醋酸盐的可及性。结果表明，微生物生物量是改变氧化铁对厌氧稻田有机碳矿化影响的关键驱动因素。