Polyethylene microplastic-induced microbial shifts affected greenhouse gas emissions during litter decomposition in coastal wetland sediments

Microplastic contamination has become increasingly aggravated in coastal environments, further affecting biogeochemical processes involved with microbial community shifts. As a key biogeochemical process mainly driven by microbiota in coastal wetland sediments, litter decomposition contributes greatly to the global greenhouse gas (GHG) budget. However, under microplastic pollution, the relationship between microbial alterations and GHG emissions during litter decomposition in coastal wetlands remains largely unknown. Here, we explored the microbial mechanism by which polyethylene microplastic (PE-MP) influenced greenhouse gas (i.e., CH4, CO2 and N2O) emissions during litter decomposition in coastal sediments through a 75-day microcosm experiment. During litter decomposition, PE-MP exposure significantly decreased cumulative CH4 and CO2 emissions by 41.07% and 25.79%, respectively. However, there was no significant change in cumulative N2O emissions under PE-MP exposure. The bacterial, archaeal, and fungal communities in sediments exhibited varied responses to PE-MP exposure over time, as reflected by the altered structure and changed functional groups of the microbiota. The altered microbial functional groups ascribed to PE-MP exposure and sediment property changes might contribute to suppressing CH4 and CO2 emissions during litter decomposition. This study yielded valuable information regarding the effects of PE-MP on GHG emissions during litter decomposition in coastal wetland sediments.

Long term effects of fire on the soil greenhouse gas balance of an old-growth temperate rainforest

Forest fires can cause great changes in the composition, structure and functioning of forest ecosystems. We studied the effects of a fire that occurred >50 years ago in a temperate rainforest that caused flooding conditions in a Placic Andosol to evaluate how long these effects last; we hypothesized that the effects of fire on the soil greenhouse gas (GHG) balance could last for many years. We made monthly measurements of fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) during two years of soils in an unburned forest (UF) and a nearby site that burned >50 years ago (BS). Our results show that CO₂ emissions from soils were higher in the UF than in the BS, and positively correlated with temperature and negatively with soil water content at both sites. Both sites were net CH₄ sinks (higher in the UF) and fluxes correlated positively with soil water content and negatively with temperature (stronger relation in the BS). Emissions of N₂O were low at both sites and showed correlation with friction velocity at the UF site. The soil GHG balance showed that the UF emitted about 80% more than the BS (5079 ± 1772 and 2815 ± 1447 g CO₂-eq m^-2 y^-1, respectively). Combining our measured fluxes with data of CO₂ net ecosystem exchange, we estimated that at the ecosystem level, the UF was a GHG sink while the BS was a source, showing a long-lasting effect of the fire and the importance of preserving these forest ecosystems.

Estimating greenhouse gas emissions at the soil-atmosphere interface in forested watersheds of the US Northeast

Although anthropogenic emissions of greenhouse gases (GHG: CO2, CH4, N2O) are unequivocally tied to climate change, natural systems such as forests have the potential to affect GHG concentration in the atmosphere. Our study reports GHG emissions as CO2, CH4, N2O, and CO2eq fluxes across a range of landscape hydrogeomorphic classes (wetlands, riparian areas, lower hillslopes, upper hillslopes) in a forested watershed of the Northeastern USA and assesses the usability of the topographic wetness index (TWI) as a tool to identify distinct landscape geomorphic classes to aid in the development of GHG budgets at the soil atmosphere interface at the watershed scale. Wetlands were hot spots of GHG production (in CO2eq) in the landscape owing to large CH4 emission. However, on an areal basis, the lower hillslope class had the greatest influence on the net watershed CO2eq efflux, mainly because it encompassed the largest proportion of the study watershed (54 %) and had high CO2 fluxes relative to other land classes. On an annual basis, summer, fall, winter, and spring accounted for 40, 27, 9, and 24 % of total CO2eq emissions, respectively. When compared to other approaches (e.g., random or systematic sampling design), the TWI landscape classification method was successful in identifying dominant landscape hydrogeomorphic classes and offered the possibility of systematically accounting for small areas of the watershed (e.g., wetlands) that have a disproportionate effect on total GHG emissions. Overall, results indicate that soil CO2eq efflux in the Archer Creek Watershed may exceed C uptake by live trees under current conditions.