The global-scale impacts of metallic nanoparticles on soil carbon dioxide emissions

Terrestrial ecosystems are increasingly being exposed to metallic nanoparticles (MNPs). However, the global-scale impact of MNPs on soil carbon dioxide (CO2) emission remains unknown, limiting our understanding of the role of MNPs in global carbon cycle. We compiled a dataset comprising 1764 pairs of experimental observations to investigate the effects of MNPs exposure on soil respiration parameters, including respiration rates, related enzyme activities, and microbial variables. We found that MNPs could stimulate or suppress soil basal respiration rates across global environments, depending largely on the type of MNPs. We further showed that, although the inhibition of MNPs on most enzyme activities peaked in short-term exposure (<= 28 days), prolonged exposure to MNPs still inhibited soil organic carbon degradation. Finally, we determined that environmental conditions (e.g., soil pH and presence/absence of plants) were also important regulators of the influence of MNPs on soil respiration parameters. Our findings underline that the effects of MNPs on soil CO2 emission depended on MNPs type, exposure design, and environmental factors, which is critical for predicting the role of MNPs in influencing the global carbon cycle and climate change.