Carbon isotope dynamics during leaf litter decomposition with reference to lignin fractions

We studied the dynamics of the stable C isotope ratio (δ 13 C) of Swida controversa and Fagus crenata leaf litter during decomposition for 35 months with reference to the relative enrichment of the residue by lignin fraction‐derived C. The study was carried out on upper and lower parts of a forest slope in a cool temperate forest in Japan. The enrichment of lignin fraction‐C was associated with a decrease in the δ 13 C of S. controversa residue. The decrease in δ 13 C was greater at the lower than the upper site for S. controversa . In contrast, the relative increase in lignin fractions in F. crenata residue was not associated with the changes of δ 13 C. 13 C nuclear magnetic resonance analysis, which revealed the relative decrease in alkyl‐C and O‐alkyl‐C and the relative increase in aromatic‐C and carbonyl‐C, provided further evidence for the contribution of the selective preservation of lignin of plant origin to the increase in the lignin fraction.