Microplastics Generate Less Mineral Protection of Soil Carbon and More CO₂ Emissions

Area of Science:

• Environmental Science
• Soil Science
• Biogeochemistry

Background:

• Microplastic pollution is a growing concern in terrestrial ecosystems.
• Microplastics can release carbon-based compounds, potentially impacting soil carbon dynamics.
• The influence of microplastic-derived dissolved organic matter (MP-DOM) on carbon mineralization and sequestration is largely unknown.

Purpose of the Study:

• To investigate the bioavailability of MP-DOM in soils.
• To determine the contribution of MP-DOM to the soil mineral-associated carbon pool.
• To elucidate the mechanisms behind MP-DOM's effects on soil carbon cycling.

Main Methods:

• Microcosm experiments were used to assess MP-DOM bioavailability and soil carbon sequestration.
• Spectroscopic and molecular signatures of MP-DOM were analyzed.
• Sorption properties of MP-DOM on model minerals were compared to natural organic matter (NOM).

Main Results:

• MP-DOM significantly increased CO2 emissions (21-576%) and decreased mineral-associated organic carbon (34-83%) compared to NOM.
• Biodegradable microplastics yielded higher CO2 emissions than conventional microplastics.
• MP-DOM exhibited higher lability (7.96x) and lower mineral sorption (3.96x) than NOM due to lower humification and fewer polar groups.

Conclusions:

• Microplastics can destabilize soil carbon stocks, exacerbating climate change.
• MP-DOM's properties enhance microbial utilization and reduce carbon sequestration in soils.
• Understanding MP-DOM's impact is crucial for assessing terrestrial carbon cycling under microplastic pollution.