Mixed-species plantation with Pinus massoniana and Castanopsis hystrix accelerates C loss in recalcitrant coniferous litter but slows C loss in labile broadleaf litter in southern China

Litter decomposition varies with forest type in complex ways and is significantly dependent on tree species diversity. A field litterbag experiment was conducted in monospecific and mixed-species plantations of Pinus massoniana and Castanopsis hystrix in subtropical China, to examine the effects of litter mixing and changing stand environment on the litter decomposition rate and the composition-specific litter organic C loss rate of P. massoniana and C. hystrix. Admixing with the lower-quality P. massoniana litter slowed C. hystrix litter decomposition and recalcitrant C loss, whereas admixing with the higher-quality C. hystrix litter hastened P. massoniana litter decomposition in the mixed-species plantation. The P. massoniana litter exhibited a faster decomposition rate in the mixed-species plantation than in the P. massoniana monospecific plantation. The same trend was found in the loss rates of aromatic C and carbonyl C from P. massoniana litter. The greater soil organic matter content and nitrogen availability in the mixed-species plantation than in the P. massoniana monospecific plantation could have resulted in the increased rates of decomposition and organic C loss in P. massoniana litter. This study highlights that maintaining mixed conifer-broadleaf forests and/or adopting close-to-nature forest management could accelerate the decomposition of recalcitrant coniferous litter, facilitating C sequestration and mitigating the C emissions derived from the labile broadleaf litter.