Changes in leaf litter decomposition of primary Korean pine forests after degradation succession into secondary broad-leaved forests

Forest degradation succession often leads to changes in forest ecosystem
functioning. Exactly how the decomposition of leaf litter is affected in a
disturbed forest remains unknown. Therefore, in our study, we selected a
primary Korean pine forest (PK) and a secondary broad-leaved
forest (SF) affected by clear-cutting degradation, both in Northeast
China. The aim was to explore the response to changes in the leaf litter
decomposition converting PK to SF. The mixed litters of PK and SF were
decomposed in situ (one year). The proportion of remaining litter mass,
main chemistry, and soil biotic and abiotic factors were assessed during
decomposition and then we made an in-depth analysis of the changes in the
leaf litter decomposition. According to our results, leaf litter
decomposition rate was significantly higher in the PK than that in the SF.
Overall, the remaining percent mass of leaf litter’s main chemical quality
in SF was higher than in PK, indicating that leaf litter chemical turnover
in PK was relatively faster. PK had a significantly higher amount of total
phospholipid fatty acids (PLFAs) than SF during decomposition. Based on
multivariate regression trees, the forest type influenced the soil habitat
factors related to leaf litter decomposition more than decomposition time.
Structural equation modeling revealed that litter N was strongly and
positively affecting litter decomposition, and the changes in
actinomycetes PLFA biomass played a more important role among all the
functional groups. Selected soil abiotic factors were indirectly driving
litter decomposition through coupling with actinomycetes. This study
provides evidence for the complex interactions between leaf litter
substrate and soil physical-chemical properties in affecting litter
decomposition via soil microorganisms.