Similar mineral-associated organic carbon formation but distinct efficiencies by powdered wollastonite addition between two soils

Recent studies showed that application of silicates powders (e.g., wollastonite) to soils can enhance soil organic carbon (SOC) sequestration. However, whether and how the formation of mineral-associated organic carbon (MAOC) is affected by this practice is largely unknown. Here, we added ¹³C-labeled glucose at a rate of 5 % SOC to a forest and a farmland soil with and without CaSiO₃ powder (analytical grade) addition (5 % of oven-dried soil mass) in a 60-day incubation experiment. Microbial carbon use efficiency (CUE) and biomass turnover were measured using a¹⁸O labelling method. We found that ¹³C-mineral associated organic carbon (¹³C-MAOC) was significantly increased by ∼ 171 % in the forest soil, and by ∼ 252 % in the farmland soil by CaSiO₃ addition. CaSiO₃ addition also significantly increased ¹³C-particulate organic carbon (¹³C-POC) by 156 % in the farmland soil. As such, the forest soil had a higher percentage of ¹³C-MAOC formed relative to ¹³C-POC than the farmland soil. The increased ¹³C-MAOC in the forest soil is likely related to the increased microbial CUE (128.5 %) due to increased pH (3.5 units). Despite no significant increase in microbial CUE, CaSiO₃ addition decreased glucose-derived CO₂ in the farmland soil relative to the forest soil. These results suggest that more glucose may have been utilized in the anabolic pathway by microorganisms, leading to higher MAOC formation efficiency in the farmland soil than the forest soil. Overall, our results highlight that CaSiO₃ addition can promote MAOC formation, but the efficiency may depend on soil type.