Impact of tree litter decomposition on soil biochemical properties obtained from a temperate secondary forest in Northeast China

Conversion of secondary forests to larch plantations results in a reduction in quantity and quality of plant litters entering the soil and may reduce the soil nutrient cycling rate. As a major process influencing soil nutrient cycling and biochemical properties, leaf litter decomposition has received little attention in temperate secondary forest systems. This study aimed to assess the decomposition of tree litters of varying quality and its impacts on the chemical and biological properties of soils obtained from a temperate secondary forest in a short-term experiment. In this study, impact on soil biochemical properties of tree litter originating from five dominant tree species in Northeast China (Quercus mongolica, Juglans mandshurica, Fraxinus rhynchophylla, Fraxinus mandshurica, and Acer mono) were tested. A 42-day laboratory decomposition experiment was conducted to determine the short-term influences of the decomposition of the five tree species leaf litters on secondary forest soil carbon (C) decomposition, nitrogen (N) mineralization, soil microbial biomass, soluble organic compounds in microbial biomass, enzyme activities, soluble organic C, and pH. Carbon decomposition, equivalent to 29-41 % of leaf litter C, occurred during the incubation. F. mandshurica and A. mono leaf litters decomposed faster than those of Q. mongolica, J. mandshurica, and F. rhynchophylla due to their low lignin concentration and lignin-to-N ratio and high labile C pool. In contrast, F. mandshurica and A. mono leaf litters immobilized less N than the other three leaf litters, which affected N availability. Soil amended with F. mandshurica leaf litter had higher microbial biomass C than the other four leaf litters, indicating that F. mandshurica could increase soil nutrient cycling. The five leaf litter types all increased activities of exoglucanase, -glucosidase, and N-acetyl--glucosaminidase, but there were no effects on phenol oxidase activity. This study suggested that litter of F. mandshurica incorporated in soils tends to decompose faster than litter of other species and increases the microbial biomass. F. mandshurica is, therefore, more advantageous than the other studied tree species for increasing nutrient cycling in a temperate secondary forest soil in this short-term laboratory incubation experiment. Future studies should consider the interactions among soil types, different climates, and long-term decomposition of leaf litters.