Detrital Inputs Regulate Condensed Aromatic Carbon Persistence in Forest Soils

Abstract

Condensed aromatic carbon (ConAC) is widely recognized as a chemically recalcitrant component of soil organic matter. However, its stock and potential transformation into dissolved condensed aromatic carbon (dConAC) in forest soils may be altered in response to environmental changes that alter forest litter production. Using three decades of detrital input and removal treatments in a temperate forest, we investigated bulk ConAC and dConAC in soil profiles with the benzene polycarboxylic acid method. Doubling litter inputs (Double Litter) did not increase ConAC content or stocks, but instead promoted ConAC oxidation to dConAC in surface soils (0–10 cm), evidenced by the higher benzene hexacarboxylic acid-to-benzene pentacarboxylic acid ratio and increased dConAC proportions in both ConAC and dissolved organic carbon pools. Litter removal (No Litter) and its combination with root exclusion (No Inputs) reduced surface-soil ConAC, consistent with decreased ConAC-carrying aboveground litter inputs; No Inputs lowered ConAC stocks throughout the 0–50 cm profile, likely due to intensified microbial utilization of ConAC under substrate limitation. Overall, forest soil ConAC stocks appear relatively resistant to detrital input changes, but enhanced ConAC-to-dConAC conversion highlights a pathway for increased terrestrial–aquatic ConAC fluxes with implications for ConAC cycling under future climate and land-use change.