Labile carbon release from plant litter and its effect on soil organic matter formation in a subtropical forest

Plant litter is a primary source of soil organic matter (SOM) in forests, but which carbon (C) fraction of plant litter contributes directly to SOM formation remains not fully understood.

We conducted a 2.5-year microcosm experiment in a subtropical forest to assess C release during Cinnamomum camphora litter (leaf and twig) decomposition. We also evaluated the temporal changes in soil microbial biomass (phospholipid fatty acids, PLFAs), enzymatic activities and soil C fractions with or without litter input until the foliar litter is decomposed by approximately 80%.

Decomposition rates of total C, dissolved organic C, hot-water extractable C, non-structural C, soluble sugars and starch in foliar litter estimated by the first-order exponential model were 0.689, 2.310, 8.272, 1.032, 13.509 and 0.718 yr⁻¹, respectively. For twig litter, these rates were 0.359, 4.085, 2.756, 0.847, 2.274 and 0.675 yr⁻¹, respectively. The C inputs from decomposing litter increased soil PLFAs at early periods, but did not significantly change soil enzymatic activities. Although soil particulate and mineral-associated organic C were not changed significantly, litter C input significantly increased the concentrations of soil non-structural C, soluble sugars and starch, which corresponded to labile C release from decomposing litter.

Our findings suggested that the short-term effect of litter input on SOM formation is primarily driven by labile C input from decomposing litter in this subtropical forest.