Moisture Associated Microbial Communities in Antarctic Dry Valley Soils

• Main Author: Anderson, Rachelle
• Other Authors: Cary, S. Craig
• Format: Thesis
• Language: English
• Published: University of Waikato 2017
• Subjects: Climate change; microbial community; soil; in situ; Dry Valley; Antarctica; water track; moisture; relative humidity; temperature; UV; bio-indicator; Antarctic; Miers; Miers Valley; Antarc*
• Online Access: https://hdl.handle.net/10289/11346

Climate change is having a dramatic impact on the natural environment and is one of the most imminent and important issues of the 21st century. With limited vegetation and few large terrestrial organisms, Antarctica offers a unique opportunity to understand the impact of abiotic, climatic factors on microbial ecosystems (free of many of the confounding biological variables in more complex systems). Recent in situ studies indicate that microbial communities within Antarctic soils may respond to environmental changes within far shorter time frames than originally believed. In a landmark study, Tiao et al. (2012) investigated the rate at which microbial communities responded to a unique soil modification experiment. To this end, a mummified seal carcass (dated at 250 years) was shifted from its original site in Miers Valley, to a new, geomorphically similar site in close proximity. Remarkably, increased microbial biomass, decreased biodiversity, and shifts in the microbial community composition were observed within just two summers. While the seal carcass altered the underlying soil’s nitrogen and organic carbon content, pH, and conductivity; statistical analysis revealed that none of these physicochemical changes could satisfactorily explain the changes in the microbial community. Instead the data suggest that the changes observed may have been caused by physical, abiotic factors induced by the seal carcass (i.e. increased and more stable relative humidity (RH), reduced UV exposure, and reduced daily temperature fluctuations). However, due to the un-replicated, observational nature of the study, this is merely speculation. In order to verify these findings and resolve the drivers of the microbial community changes observed, a controlled, in situ experiment was designed to replicate the abiotic effects of the seal carcass (stabilise temperature, reduce UV exposure, and increase and stabilise RH in the underlying soil). To do this, overturned or upright black and translucent plastic trays were set up on undisturbed regions of Antarctic Dry Valley soil; soil samples were taken every January for a five-year period; and Ion Torrent sequencing of 16S rRNA gene amplicons was used to assess changes in the microbial community composition and structure. However, based on RH data and visual observations of the site it would appear that the tray experiment was unknowingly set up in either a flat, low lying area where moisture accumulated; or in a subsurface water track. Due to the constant high moisture content within the soil on which the experiment was deployed, the effect of the tray treatments on the local environment (i.e. RH and temperature) was negligible. The microbial community composition in the tray treatment experiment stayed quite consistent across all years and treatments, however there was a significantly greater abundance of Cyanobacteria/ Chloroplasts in the translucent overturned (TO) treatment than in the black upright (BU) or black overturned (BO) treatments. Interestingly, the moist tray treatment soil had a greater relative abundance of Cyanobacteria/ Chloroplasts, Proteobacteria, and Bacteroidetes than the drier seal control site, in keeping with the observations of other studies investigating microbial community composition within wet environments. These findings hint at the importance of small-scale topographic factors in microbial community structure, and/or highlight the potential of using microbial community composition as a bio-indicator of hidden water tracks.