Dynamics and speciation of organic carbon during decomposition of leaf litter and fine roots in four subtropical plantations of China

Plant litter and fine roots turnover are important carbon (C) inputs to soil and a direct emission source of CO2 to the atmosphere. C dynamics during litter decomposition provide an insight into C flow in soils. To quantitatively assess how decomposition processes vary with litter types, the solid-state 13C nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS-NMR) technique was applied to analyze the organic C dynamics of conifer (Pinus massoniana) and broadleaf (Castanopsis hystrix, Michelia macclurei and Mytilaria laosensis) leaf litter and fine roots which had degraded during one year litterbag experiment in four subtropical plantations of China. The results were used to estimate decomposition rates of different C types and compositional changes of leaf litter and fine roots during decomposition. The mass loss rates of different C fractions during decomposition varied significantly between litter types. Site environment and initial litter quality played more critical roles in regulating decomposition of fine roots than of leaf litter. The significant changes in the proportion of C forms and degree of humification occurred during leaf litter decomposition, but not during fine roots decomposition. The proportions of alkyl C and carbonyl C and alkyl/O-alkyl C ratio varied with leaf litter types, with an increase for the proportion of alkyl C and alkyl/O-alkyl C ratio in broadleaf leaf litters and an enhanced trend for the proportion of carbonyl C for P. massoniana. The results suggest that the patterns and main controlling factors of litter C compositional change during decomposition differed between above- and belowground, and the dynamics of leaf litter C fractions during decomposition differed between conifer and broadleaf species. The findings of litter C compositional decomposition of the main tree species in this study could contribute to the accurate estimation of soil C sequestration in subtropical plantation ecosystems.

► The k values of different C fractions varied significantly between litter types. Soil moisture and litter quality were critical to fine roots C forms decomposition. The changes in proportion of C fractions occurred during leaf litter decomposition.