Changes in fine root decomposition of primary Pinus koraiensis forest after clear cutting and restoration succession into secondary broad-leaved forest

Abstract

Fine root decomposition is one of the primary mechanisms by which nutrient uptake and C exchange occur in terrestrial ecosystems, which will be likely affected by forest succession. Herein, we compared the fine root decomposition rates of primary Korean pine forest (PK) and secondary broad-leaved forest (SF) using the litter bag method; then conducted an in-depth analysis of differences in the PK and SF fine root decomposition process. Our results demonstrated that the fine root decomposition in PK was significantly faster than that in SF. In general, the percent (%) mass of the main nutrient elements remaining in SF fine roots was significantly higher than that in PK, indicating that PK can more efficiently return soil nutrients through fine root decomposition. We also found that the succession of PF to SF induced significant alternation of the microbial community composition and decreased activities of soil enzymes. Structural equation modeling further demonstrated that fine root K and lignin were the key substrate-level factors affecting fine root decomposition, while actinomycetes and fungi PLFA biomass change played the most important role among all the functional groups. Finally, we determined that fine root degradation was driven by polyphenol oxidase and acid phosphatase enzymatic activities. This study elucidates the complex interactions between fine root substrate and soil physiochemical properties and demonstrates how they affect fine root decomposition via soil microorganisms. Given that these changes continue over long time scales, the secondary forest will experience increased difficulty return to the original primary Korean pine broad-leaved forest vegetation.