The impact of biodegradable microplastics on soil priming effects in poplar shelterbelts across an afforestation gradient

Abstract The widespread agricultural use of biodegradable plastics may cause the persistence of biodegradable microplastics (BMPs) in afforested soils, which could compromise the soil organic carbon (SOC) sequestration in shelterbelts through priming effects. However, the influence of BMPs on SOC priming effects across different afforestation gradients remains unclear. Polyhydroxyalkanoates (PHA) and polylactic acid (PLA), two typical BMPs, were investigated for their influence on the priming effect in soils collected from abandoned farmland and poplar shelterbelts aged 5, 10, 15 and 20 years (5‐, 10‐, 15‐ and 20‐year stands). The difference in isotopic values (δ 13 C) between BMPs and SOC (>10‰) was employed to differentiate the sources of CO 2 emissions. Our results showed that PHA and PLA induced positive priming effects across the afforestation gradient through modifying soil physicochemical and aggregate properties, as well as reshaping bacterial community composition via these changes. The priming effects of PHA and PLA ranged from 83.00% to 295.41% and from 9.79% to 80.91%, respectively. Both effects initially increased and then decreased along the afforestation gradient, a trend that may be partly explained by the contrasting patterns of SOC content and the C/N ratio. Synthesis and applications . This short‐term experiment demonstrated that BMPs induced stronger positive priming in 5‐, 10‐ and 15‐year stands than in abandoned farmland, peaking at 10‐ and 15‐year stands. Therefore, to minimize BMP‐induced SOC loss in afforested soils, we recommend: (1) assess BMP contamination pre‐afforestation, prioritizing low‐risk sites and applying remediation where needed; (2) enhance post‐afforestation monitoring of BMP contamination, particularly in 10‐ and 15‐year stands.