Rock powder application alters soil pore architecture and microbial activity associated with carbon cycling

Soil pore size distribution regulates carbon (C) cycling and stabilization by controlling microbial access and organic matter protection, yet the role of rock powders (RP) in altering pore architecture and inducing physical exclusion remains poorly explored. This study evaluated the effects of RP on soil microporosity (SM), microbial biomass carbon (MBC), and dehydrogenase activity (DHA). An incubation experiment was conducted using soil amended with phonolite (Ph), diabase (Di), and granite (Gr). All treatments received 124 mg C as artificial root exudates every 14 days, and after 180 days of incubation, SM, MBC, and DHA were quantified. RP application reduced DHA relative to the control, with mean values of 8.09 (Gr), 11.24 (Di), and 11.35 (Ph), while the control exhibited the highest activity (15.65). MBC was lowest in the Gr (0.57), intermediate in the control (0.69), and highest in Ph (0.82). The pore restriction index, calculated as the ratio between pores < 1 µm and pores ranging from 6-30 µm plus 30-100 µm, was higher in all RP (1.12-1.25) than in the control (0.77), indicating increased physical restriction. Pearson correlation analysis revealed a negative association between pores < 1 µm and DHA in soils amended with Di (r = -0.639, p = 0.08) and Ph (r = -0.827, p = 0.01). Specific DHA activity (DHA/MBC) was highest in the control (23.17) and lower in Gr (14.28) and Ph (13.87). Overall, RP alter soil pore architecture by increasing micropore dominance and physically restricting microbial activity, potentially enhancing C stabilization in soils.