Contribution of maize root derived C to soil organic carbon throughout an agricultural soil profile assessed by compound specific 13C analysis

Cutin and suberin structural units might be stabilized in subsoils and contribute to the aliphatic structures observed in stabilized soil organic matter (SOM). We studied their dynamics in subsoils by measuring the concentrations and 13 C contents of cutin and suberin markers in soil profiles under wheat (C3) and after 9 years of maize cropping (C4 plant). Alkandioic acids were considered as markers for roots, midchain hydroxy acids were only present in shoots and x-hydroxy acids were identified in both roots and shoots. The diacid concentrations greatly increased below the ploughed layer after 9 years of maize cropping, possibly due to a higher root density of maize compared to wheat or to a faster turnover of fine roots and increased exudation of maize compared to wheat. From 0–75 cm, 9 years of maize cropping did not affect the distribution of shoot biomarkers but increased their concentrations. By contrast, below 75 cm, the shoot marker concentrations drastically decreased from the wheat control to the 9 year maize soil. The difference of d 13 C observed for shoot markers was always lower than that observed for