Comparison of soil chemical and microbial properties in monoculture larch and mixed plantations in a temperate forest ecosystem in Northeast China

BACKGROUND: The introduction of broadleaved tree species in monoculture larch plantations to establish mixed plantations is a feasible way to improve soil properties. However, our understanding of how mixed plantations of larch and broadleaved tree species affect soil properties, particularly microbial community structures and functions, remains limited. We compared three paired monoculture larch (Larix gmelinii) and mixed [L. gmelinii–Fraxinus mandshurica (a dominant broadleaved species)] plantations to investigate the effect of a larch–broadleaved tree species combination on the carbon (C) and nitrogen (N) content, abundance and composition of microbial communities, and enzyme activities associated with litter and soil. RESULTS: The bacterial abundance in the litter, soil N availability, pH and electronic conductivity were significantly higher in the mixed-species plantation in comparison with those of the monoculture plantation. However, in the litter of mixed-species plantation, the relative levels of Agaricomycetes fungi were lower than those of the monoculture plantation, indicating that soil fungal communities were affected more than bacterial communities. In contrast, soil in the mixed-species plantation showed increased exoglucanase and N-acetyl-β-glucosaminidase activities. However, the C and N levels, δ¹³C and δ¹⁵N values, and fungal abundance in litter and soil were not significantly different between the monoculture and mixed-species plantations. CONCLUSIONS: Our findings suggest that fungal community compositions and enzyme activities are sensitive to the introduction of broadleaved tree species into larch plantations. Thus, these parameters can be used as important indicators to evaluate the effects of tree species selection on soil restoration.