Artificial Warming Effect on Microbial Community and Humic Substance Degradation in Maritime Antarctic Soil in King George Island

Abstract

Although the maritime Antarctic has undergone rapid warming, the effects on indigenous soil-inhabiting microorganisms are not well known. Artificial warming experiments using open-top chamber (OTC) have been performed on the Fildes Peninsula in the maritime Antarctic since 2008. When the soil temperature was measured at a depth of 25 cm during the 20132015 summer seasons, the mean temperature inside OTC (OTC-In) increased by approximately 0.8ºC compared with outside OTC (OTC-Out), while soil chemical and physical characteristics were not changed. Soils from OTC-In and OTC-Out were subjected to analysis for change in microbial community and degradation rate of humic substances (HS, the largest pool of recalcitrant organic carbon). Archaeal and bacterial communities in OTC-In were minimally affected by warming compared with those in OTC-Out, with archaeal methanogenic Thermoplasmata slightly increased in abundance. The abundance of heterotrophic fungi Ascomycota was significantly altered in OTC-In. Total bacterial and fungal biomass in OTC-In increased by 20% compared to OTC-Out, indicating that this may be due to increased microbial degradation activity for soil organic matter (SOM) including HS, which would result in the release of more low-molecular-weight growth substrates from SOM. Despite the effects of warming on the microbial community over the 8-years-experiments warming did not induce any detectable change in content or structure of polymeric HS.