Effects of particulate matter (PM2.5) and associated acidity on ecosystem functioning: response of leaf litter breakdown

Particulate matter (PM2.5 with the diameter ≤ 2.5 μm) as one of the most harmful and complex pollutants can reduce environment quality and affect human health. Through acidification by wet deposition, PM2.5 can cause acid rain to impact aquatic ecosystems. However, our understanding of PM2.5 effect on ecosystem functioning is highly limited. This study investigated the relationship between PM2.5 concentration, associated acidity, and leaf litter breakdown of three tree species in laboratory experimental mesocosms, which are weeping willow (Salix babylonica), camphor tree(Cinnamomum camphora), and the south magnolia (Magnolia grandiflora). We found that leaf litter breakdown was significant affected by PM2.5 and associated acidity. With the increase of acidity, the leaf breakdown rate of all three tree species decreased. With the increase of PM2.5 concentration, the leaf breakdown rates of those leaves slowed down. When considering the influence of leaf toughness, willow leaves with lower toughness had a higher breakdown rate than that of camphor tree and the south magnolia. Our study suggests that PM2.5 has significant impact on the aquatic ecosystem functioning through increasing acidification in aquatic environment. Hence, along with ecological restoration of local aquatic habitats, further freshwater ecosystem management should include reducing air pollution through regional efforts of best ecosystem management.