Lithological Controls\non Soil Aggregates and Minerals\nRegulate Microbial Carbon Use Efficiency and Necromass Stability

Microbial carbon (C) use efficiency (CUE) drives soil\nC formation,\nwhile physical-chemical protection stabilizes subsequent microbial\nnecromass, both shaped by soil aggregates and minerals. Soils inherit\nmany properties from the parent material, yet the influence of lithology\nand associated soil geochemistry on microbial CUE and necromass stabilization\nremains unknow. Here, we quantified microbial CUE in well-aggregated\nbulk soils and crushed aggregates, as well as microbial necromass\nin bulk soils and the mineral-associated organic matter fraction,\noriginating from carbonate-containing (karst) and carbonate-free (clastic\nrock, nonkarst) parent materials along a broad climatic gradient.\nWe found that aggregate crushing significantly increased microbial\nCUE in both karst and nonkarst soils. Additionally, compared to nonkarst\nsoils, calcium-rich karst soils increased macroaggregate stability\nand decreased the ratio of oligotrophic to copiotrophic microbial\ntaxa, leading to a reduction in microbial CUE. Moreover, microbial\nCUE was negatively associated with iron (hydr)oxides in karst soils,\nattributed to the greater abundance of iron (hydr)oxides and higher\nsoil pH. Despite the negative effects of soil aggregation and minerals\non microbial CUE, particularly in karst soils, these soils concurrently\nshowed greater microbial necromass stability through organo–mineral\nassociations compared to nonkarst soils. Consequently, (i) bedrock\nlithology mediates the effects of aggregates and minerals on microbial\nCUE and necromass stability; and (ii) balancing minerals’ dual\nroles in diminishing microbial CUE and enhancing microbial necromass\nstability is vital for optimizing soil C preservation.