Abstract
Although numerous studies have demonstrated the toxic effects of fine particulates less than 2.5 µm (PM2.5) on the health of humans, little information is available on the ecotoxicity of PM2.5. Water-soluble inorganic ions (WSII, including Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, and SO42−) can compose more than 60% of PM2.5. To better understand the possible impacts of WSII-PM2.5 on leaf litter decomposition, we conducted an experiment in which two leaf litters from oak (Quercus variabilis) and pine (Pinus massoniana) dominant forests in subtropical China were incubated in microcosms containing their respective forest soils and treated with WSII-PM2.5. Our results showed that, after six-months of decomposition, the WSII-PM2.5 treatments inhibited leaf litter decomposition rates, carbon and nitrogen loss, microbial biomass, and enzyme activities in the two forests. In addition, higher WSII-PM2.5 concentration led to stronger negative effects. Comparative analysis showed that the negative effects of WSII-PM2.5 on oak forest were greater than on pine forest, relating to the higher susceptibility to changes of soil microenvironment in oak forests. WSII-PM2.5 may influence decomposition through soil acidification and salinization, which could also cause a sub-lethal depression in soil isopod activity. However, in the first month of decomposition, mass loss of the oak and pine leaf litters under the low concentration WSII-PM2.5 were 21.63% and 35.64% higher than that under the control, respectively. This suggests that transitory low concentrations of WSII-PM2.5 have a promoting effect on decomposition. Long-term PM2.5 exposure, therefore, may have profound ecosystem consequences by altering the balance of ecosystem carbon flux, nutrient cycling, and humus formation in the future.
Highlights
Airborne pollutants are often microscopic particulates, which can come from factories, power plants, refuse incinerators, motor vehicles, construction activity, fires, and natural windblown dust [1,2].Particulate matter (PM) is a harmful form of air pollution due to its ability to penetrate deep into the lungs and bloodstream unfiltered, causing permanent DNA mutations, heart attacks, respiratory disease, and premature death [3,4]
After six-months of decomposition, the average soil pH values were higher in the pine forest than in the oak forest under all water-soluble inorganic ions (WSII)–PM2.5 treatments (Tukey0 s test, p < 0.001, Table 3)
The decreases in soil pH values with WSII–PM2.5 treatments were greater in oak forest (PML—2.28%, PMM—3.65%, PMH—4.34%) than in pine forest (PML—0.65%, PMM—1.73%, PMH—2.16%)
Summary
Airborne pollutants are often microscopic particulates, which can come from factories, power plants, refuse incinerators, motor vehicles, construction activity, fires, and natural windblown dust [1,2].Particulate matter (PM) is a harmful form of air pollution due to its ability to penetrate deep into the lungs and bloodstream unfiltered, causing permanent DNA mutations, heart attacks, respiratory disease, and premature death [3,4]. An increasing number of studies are focused on this class of pollutants [6,7,8]. Zhao et al [6] found that acute exposure to high concentrations of PM2.5 and prolonged exposure to low concentrations of PM2.5 resulted in adverse effects on development, lifespan, reproduction, locomotive behavior, and intestinal development of nematodes (Caenorhabditis elegans). Hartono et al [7] showed that high PM2.5 deposition in water bodies, associated with acidification, had an adverse effect on aquatic organisms. Wu and Zhang [8] found that PM2.5 had a significant impact on aquatic ecosystem function, such as leaf litter decomposition, through increasing acidification in aquatic environments
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