Microbial groups and their functions control the decomposition of coniferous litter: A comparison with broadleaved tree litters

The conversion of secondary forests to pure coniferous plantations leads to a decrease in soil quality partly because of the slow decomposition rate of coniferous litter. Microbial decomposers directly regulate the decomposition process. However, lithe is known about how litter type and microbial communities including both bacteria and fungi interact to affect decomposition rates. A field experiment was performed consisting of seven treatments (i.e., four tree litters: Quercus mongolica, Juglans mandshurica, Acer mono, and Larbc gmelinii) in which either monospecific litters or mixtures of larch litter with each broadleaved tree litter (mass ratio was 1:1) were placed into litterbags, and the microbial community composition and enzyme activities were measured. The results showed that in monospecific litters, the highest mass loss was observed in Acer litter, followed by Quercus, Juglans, and Larbc litters. Furthermore, synergistic non-additive mixture effects were found in the Larbc-Acer and Larbc-Quercus mixtures. Most of the abundant bacterial taxa and potential functional genes encoding the hydrolytic enzymes were not significantly affected by the litter type. In contrast, each litter type was characterized by a specific fungal community, as well as different patterns of extracellular enzyme activity. The most abundant fungal decomposers in Larbc litter during the first 540 days of decomposition, such as Meria, Lambertella, Venturia, and Ochroconis, were negatively correlated with most of the enzymatic activities, which possibly explains the slower decomposition rate of Larbc litter. In conclusion, mixing Larbc litter with broadleaved litters could change the microbial community composition, and accelerate the decomposition of hemicelluloses and lignin. Introducing broadleaved tree species with fast litter turnover rates by allowing natural regeneration and planting broadleaved tree species in pure larch plantations may be an effective way to restore soil quality in temperate forest regions.