Soil Decomposer Can Regulate the Legacy Effect of Photodegradation on Forest Marcescent Litter Decomposition, but Emerging Microplastics Disrupt This

Abstract

Photodegradation—photochemical mineralization of standing litters—often exerts a legacy effect aiding biodegradation in soil (PLE), which is overlooked in deciduous forests containing marcescent leaves. Meanwhile, increasing anthropogenic microplastics have deposited in forests, how they would affect the PLE on subsequent litter bio-decomposition is currently unknown. Here, we employed an ultraviolet-accelerated aging chamber to replicate the abiotic photodegradation process of a naturally marcescent tree, Lindera glauca, then manipulated mesocosm bio-incubations to quantify how decomposers (microbial alone or with soil animals) and microplastic contamination would interactively affect the PLE. We found abiotic photodegradation significantly decreased litter lignin content before and after the bio-incubation. During an early phase decomposition, lignin lost greatly and displayed a crucial role in determining the ways that soil animal and photodegradation affect the bio-decomposition. Microbial decomposer alone led to a positive PLE universally. Soil animals depressed microbial biomass and inhibited the microbial-mediated PLE in unpolluted mesocosms but intensified the PLE in contaminated soils. We conclude that decomposer interactions can attenuate PLE, but microplastics will disrupt the established equilibrium, making contaminated soil more susceptible to photodegradation-induced litter chemical changes. This promotes integration of radiation and emerging pollution to further our understanding of biogeochemical cycle in forest ecology.