Net rhizodeposition corresponds to the portion of living root carbon (C) that remains in the soil after microbial processing and partial decomposition. Although it is assumed that this C input exerts an important role in the formation of soil organic matter (SOM), its contribution to distinct SOM pools is still not fully understood. In this study, we aimed to (i) quantify the retention of net rhizodeposition C in the different SOM fractions and in reactive Al and Fe mineral phases and (ii) investigate how rhizodeposition drives the spatial distribution of microbial communities in the rhizosphere. To track the transfer of net rhizodeposition into the soil, we used artificially labeled eucalypt ( spp.) seedlings under a C-CO atmosphere (multiple-pulse labeling). Combining physical SOM fractionation and the chemical extraction of aluminum (Al) and iron (Fe) reactive phases, we studied the distribution of net rhizodeposition into different soil fractions. We also assessed the C incorporation into microbial phospholipid fatty acids (PLFAs) at different distances from the roots. Our results show that 76 % of the net rhizodeposition C was retained within the mineral-associated organic matter (MAOM) fraction. About 28 % of net rhizodeposition C within the MAOM fraction was retained within the Al and Fe reactive phases, indicating that this is a sizeable mechanism for the retention of net rhizodeposition in soil. Rhizodeposition increased the abundance of microbial PLFAs exclusively in the soil close to the roots (0–4 mm), with prominent incorporation of net rhizodeposition C into fungal biomarkers. Overall, our findings underscore the importance of mineral associations for the retention of net rhizodeposition in the soil. We also highlight the role of fungi in transferring the root-derived C beyond the root vicinity and promoting the formation of occluded SOM.

中文翻译：

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解码根际沉积物衍生的碳进入土壤有机质的旅程

净根际沉积对应于微生物处理和部分分解后保留在土壤中的活根碳 (C) 的部分。尽管人们认为这种碳输入在土壤有机质 (SOM) 的形成中发挥着重要作用，但其对不同 SOM 库的贡献仍未完全了解。在这项研究中，我们的目的是（i）量化不同SOM组分以及活性Al和Fe矿物相中净根际沉积碳的保留，以及（ii）研究根际沉积如何驱动根际微生物群落的空间分布。为了追踪根际净沉积物向土壤中的转移，我们在 C-CO 气氛下使用了人工标记的桉树幼苗（多脉冲标记）。结合物理 SOM 分馏和铝 (Al) 和铁 (Fe) 反应相的化学萃取，我们研究了根际净沉积在不同土壤部分的分布。我们还评估了距根部不同距离处 C 与微生物磷脂脂肪酸 (PLFA) 的结合情况。我们的结果表明，76% 的净根际沉积 C 保留在矿物相关有机质 (MAOM) 部分中。MAOM 部分中约 28% 的净根际沉积 C 保留在 Al 和 Fe 反应相中，表明这是土壤中净根际沉积保留的重要机制。根际沉积增加了仅在靠近根部的土壤（0-4毫米）中微生物PLFA的丰度，并且净根际沉积C显着纳入真菌生物标志物中。总的来说，我们的研究结果强调了矿物质组合对于保留土壤中根际净沉积的重要性。我们还强调了真菌在将根部来源的 C 转移到根部附近并促进封闭 SOM 形成方面的作用。