Aquatic insect subsidies influence microbial composition and processing of detritus in near‐shore subarctic heathland

• Published in: Oikos
• Main Authors: McCary, Matthew A., Kasprzak, Madeline D., Botsch, Jamieson C., Hoekman, David, Jackson, Randall D., Gratton, Claudio
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: Ecology, Evolution, Behavior and Systematics; Mývatn; Iceland; Subarctic
• Online Access: http://dx.doi.org/10.1111/oik.08032; https://onlinelibrary.wiley.com/doi/pdf/10.1111/oik.08032; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/oik.08032

Insects are major conduits of resources moving from aquatic to terrestrial systems. While the ecological impacts of insect subsidies are well documented, the underlying mechanisms by which these resources change recipient ecosystems remain poorly understood. Most subsidy inputs enter terrestrial systems as detritus; thus, soil microbes will likely influence the processing of insect subsidies, with implications for plant community composition and net primary productivity (NPP). In a subarctic ecosystem near Lake Mývatn, Iceland where midge (Diptera: Chironomidae) deposition to land is high, we investigated how insect subsidies affected litter processing and microbial communities. We also evaluated how those belowground effects related to changes in inorganic nitrogen, plant composition and NPP. We simulated subsidies by adding midge carcasses to 1‐m 2 heathland plots, where we measured effects on decomposition rates and the plant community. We then studied how fertilization treatments (control, KNO 3 and midge‐carcass addition) affected graminoid biomass and inorganic nitrogen in greenhouse experiments. Lastly, we conducted a soil‐incubation study with a phospholipid fatty acid analysis (PLFA) to examine how midge addition to heathland soils affected microbial respiration, biomass and composition. We found that midge addition to heathland soils increased litter decomposition and graminoid plant cover by 2.6× and 2×, respectively. Greenhouse experiments revealed similar patterns, with midge carcasses increasing graminoid biomass by at least 2× and NH 4 + concentrations by 7×. Our soil‐incubation study found that midge carcasses elevated microbial respiration by 64%, microbial biomass by 43% and shifted microbial functional composition. Our findings indicate that insect subsidies can stimulate soil microbial communities and litter decomposition in subarctic heathlands, leading to increased NPP and changes in plant community composition.