The effects of a non-native insect on Antarctic soil biogeochemistry and potential greenhouse gas emissions

Terrestrial biodiversity in Antarctica is low compared to most temperate and tropical systems, resulting in nutrient-limited ecosystems characterised by low complexity. The establishment of a single non-native species can profoundly disrupt these ecosystems. One such species is the flightless midge, Eretmoptera murphyi (Diptera: Chironomidae), a fly with soil-dwelling detritivorous larvae that was accidentally introduced to Signy Island (South Orkney Islands, maritime Antarctic) from its native South Georgia (South Sandwich Islands, sub-Antarctica) in the 1960s. The fly now occurs with an overall biomass exceeding that of all native microarthropod species combined in some areas of the island. Studies have shown that high larval densities are associated with significant increases in soil nitrate concentrations, potentially impacting native flora and fauna and creating favourable conditions for further invasions by non-native species.

This study investigated the influence of E. murphyi presence on a broader range of soil biogeochemical properties, utilising advanced biochemical methods to measure nitrate, ammonia, phosphorus, total nitrogen and total carbon content. The results indicate that Signy Island soils inhabited by the fly have high organic content (~32% carbon) and are acidic (pH ~4.5). Soils colonised by E. murphyi exhibited significantly higher concentrations of nitrate and ammonia compared to control sites, while phosphate levels showed no significant difference, likely due to the acidic substrate.

The potential future impact of E. murphyi presence and climate change on greenhouse gas emissions from these soils was explored through incubation experiments. Over three-month incubations, elevated temperatures representing medium (9°C) and high (14°C) future warming scenarios increased emissions of nitrous oxide (N₂O) and carbon dioxide (CO₂) from the soils, compared to the current annual average temperature (4°C). Soils from E. murphyi-occupied sites released significantly more N₂O and CO₂ than control soils, possibly due to increased microbial activity. This may be due in part to the higher water content in E. murphyi soils, which may increase microbial abundance and activity. Methane (CH₄) emissions decreased over time in all scenarios, suggesting a shift in microbial community composition.

We suggest it is possible that E. murphyi increases microbial biomass through the introduction of its non-native microbiome, resulting in increased microbial respiration rates and, thereby, amplifying greenhouse gas emissions from Antarctic soils as temperatures rise. Notably, the observed increase in N₂O emissions suggests that E. murphyi may introduce or promote the activity of microorganisms capable of ammonia oxidation, a suggestion supported by parallel microbiome studies. In a separate study of E. murphyi’s microbiome, we confirmed the presence of archaea and bacteria known to carry out ammonia oxidation and other N₂O-producing processes, such as denitrification. Key taxa identified include Crenarchaeota, Actinobacteria, Chloroflexi, and Proteobacteria. Collectively, these findings emphasise the potential for E. murphyi to significantly alter Antarctic soil processes and contribute to climate change-driven feedback loops in these polar ecosystems.