Microplastics indirectly affect soil respiration of different-aged forest by altering microbial communities and carbon metabolism.

This study explored how microplastics impact soil respiration processes in forests of varying ages by modulating the structure of microbial communities and carbon metabolic functions. The findings indicated that the abundance of microplastics in different aged forests was approximately 600-3858 items∙kg-1. The 10-year-old Pinus massoniana forest exhibited the lowest, and the 60-year-old forest had the highest microplastic abundance. The microplastics mainly consisted of fibers (26.57-38.38 %), particles sized 0-0.1 μm (40.28-70.19 %), and black particles (6.92-43.46 %). The soil respiration rate decreases with increasing forest age. However, the microplastics indirectly modified soil respiration by influencing total organic carbon (TOC) and soil pH. The functional prediction analysis showed that metabolic pathways such as formaldehyde assimilation, ribulose monophosphate pathway, and the hydroxypropionate-hydroxybutylate cycle, were significantly correlated with microplastic abundance. Structural equation model (SEM) results suggested that microplastics affected microbial carbon metabolic demands by altering microbial community structure (0.44) or directly influencing carbon metabolic pathways (0.68). Consequently, this impacts soil CO2 emissions. The findings provide new insights into the critical role of forest soils in mitigating carbon emissions caused by microplastics.