Effects of microplastics on soil microbial necromass carbon and plant residual carbon

Abstract

Studying the effects of microplastics (MPs) on plant-derived carbon and microbial-derived carbon in soil is of great significance for understanding how polluted soil affects plant productivity, water quality maintenance, human health and climate change. This study compared the effects of various concentrations (0.5 %, 1.0 %, 1.5 %, 2.0 %, and 2.5 %, w/w) of polyethylene (PE) and biodegradable polylactic acid (PLA) MPs on soil plant- and microbial-derived carbon through a 35-day soil pot experiment and biomarker method. PLA MPs promoted phospholipid fatty acids (PLFAs). PE MPs significantly reduced PLFAs. PLA and PE reduced total amino sugars, glucosamine, galactosamine and muramic acid. PLA and PE MPs reduced microbial, bacterial, and fungal necromass carbon contents, which may be due to the promotion of rhizosphere priming effect by MPs, thereby accelerating the decomposition of microbial necromass carbon. PLA had a promoting or reducing effect on V-type phenols, S-type phenols, C-type phenols, and total lignin phenols, while PE had a reducing effect on them. The reason may be that PE indirectly leads to a decrease in plant derived carbon by reducing soil total nitrogen, hydrolytic nitrogen, cation exchange capacity, etc. In general, PLA promoted the contribution of plant residual carbon to soil organic carbon (SOC), and decreased the contribution of microbial necromass to SOC. PE decreased the contribution of plant residual and microbial necromass to SOC.