<strong>Mycorrhizae enhance reactive minerals but reduce mineral-associated carbon</strong>

Soil organic carbon (C) is the largest active C pool of Earth’s surface and is thus vital in sustaining terrestrial productivity and climate stability. Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil C dynamics. Yet, it remains unclear whether and how AMF-Root associations (i.e., mycorrhizae) interact with soil minerals to affect soil C cycling. Here we showed that the presence of both roots and AMF increased soil dissolved organic C and reactive Fe minerals, as well as litter decomposition and soil CO2 emissions. However, it reduced mineral-associated C. Also, high resolution nanoscale secondary ion mass spectrometry (NanoSIMS) images showed the existence of a thin coating (0.5-1.0 μm thick) of 56Fe16O– (Fe minerals) on the surface of 12C14N– (fungal biomass), illustrating the close physical association between fungal hyphae and soil Fe minerals. In addition, AMF genera were divergently related to reactive Fe minerals, with <em>Glomus</em> being positively but <em>Paraglomus</em> and <em>Acaulospora</em> negatively correlated with reactive Fe minerals. Moreover, the presence of roots and AMF, particularly when combined with litter addition, enhanced the abundances of several critical soil bacterial genera that are associated with the formation of reactive minerals in soils. A conceptual framework was further proposed to illustrate how AMF-root associations impact soil C cycling in the rhizosphere. Briefly, root exudates and the inoculated AMF not only stimulated the decomposition of litter and SOC and promoted the production of CO2 emission, but also drove soil C persistence by unlocking mineral elements and promoting the formation of reactive minerals. Together, these findings provide new insights into the mechanisms that underlie the formation of reactive minerals and have significant implications for understanding and managing soil C persistence.土壤有机碳（C）是地球表层最大的活性碳库，对维持陆地生产力与气候稳定至关重要。丛枝菌根真菌（AMF，Arbuscular mycorrhizal fungi）可与绝大多数陆地植物形成共生关系，并对土壤碳动态发挥关键调控作用。然而，目前尚不清楚菌根-根系共生体（即菌根）是否以及如何与土壤矿物相互作用，进而影响土壤碳循环。本研究表明，根系与AMF共同存在时，土壤溶解性有机碳、活性铁矿物含量均显著提升，枯落物分解速率与土壤CO₂排放也随之增加，但该条件下矿物结合态碳的含量会降低。此外，高分辨纳米二次离子质谱（High Resolution Nanoscale Secondary Ion Mass Spectrometry, NanoSIMS）成像结果显示，在¹²C¹⁴N⁻（真菌生物量）的表面存在一层厚度为0.5~1.0 μm的⁵⁶Fe¹⁶O⁻（铁矿物）薄层，直观证明了真菌菌丝与土壤铁矿物之间存在紧密的物理结合。进一步分析发现，不同AMF属与活性铁矿物的相关性存在分化：球囊霉属（*Glomus*）与活性铁矿物呈正相关，而副球囊霉属（*Paraglomus*）和无梗囊霉属（*Acaulospora*）则呈负相关。此外，根系与AMF共同存在的条件下（尤其是配合枯落物添加处理时），土壤中若干与活性矿物形成相关的关键细菌属的丰度会显著提升。本研究还提出了一个概念框架，用以阐释菌根-根系共生体如何影响根际土壤碳循环。简言之，根系分泌物与接种的AMF不仅可刺激枯落物与土壤有机碳的分解，促进CO₂排放，还可通过活化矿物元素与促进活性矿物形成，增强土壤碳的固持稳定性。综上，本研究结果为活性矿物的形成机制提供了新的认知视角，同时对于理解与调控土壤碳固持稳定性具有重要的指导意义。