Seasonal Metabolism Changes Across Redox Gradients in Photosynthetic Mats, Lake Fryxell, Antarctica

In the McMurdo Dry Valleys (MDV), the permanently ice-covered lakes are unusual aquatic environments that are home to unique communities of microbes. Mats of photosynthetic microbes grow on the floors of these lakes and are an important part of the ecosystems in MDV environments. They experience extreme seasonality that includes the challenge of months of winter darkness. Mats cannot photosynthesize during winter, but they do remain active, and this can impact their ability to respond when spring/summer conditions arrive. To understand these impacts, it is essential to study the seasonal differences in mat organism activity, particularly during winter and then during the transition to spring sunlight. This project aims to characterize winter season activity and chemistry in benthic microbial mats in Lake Fryxell, McMurdo Dry Valleys, Antarctica. To access winter-like conditions, temporary shades will be installed over mats to “extend” dark winter conditions into spring, when field access is possible. By sampling in extended winter and spring/summer this project will determine the changes in benthic mat community composition, identify interactions between cell activity and water chemistry, and understand the effects of spring photosynthesis initiation on mats that become anoxic over winter. The permanently ice-covered lakes of the McMurdo Dry Valleys (MDV) are home to unique communities of microbes. Benthic mats of photosynthetic cyanobacteria are present in these lakes and are an important part of the primary productivity for ecosystems in MDV environments. Winter darkness inhibits mat photosynthesis, leading to anoxic conditions, limited viable metabolisms, and changes in mat biogeochemistry. With the return of sunlight photosynthesis begins again and metabolism and biogeochemistry changes. To better understand the interdependencies and impacts of these transitions, the project will characterize seasonal microbial diversity and metabolic differences in benthic mats, and the ecosystem effects caused by spring oxygen production in Lake Fryxell, McMurdo Dry Valleys, Antarctica. To access winter-like conditions, temporary shades will be installed over mats to “extend” dark winter conditions into spring, when field access is possible. The project will characterize the metabolic changes in mat communities using metagenomic and metatranscriptomic methods, in conjunction with pore water dissolved oxygen and sulfide measurements from the environment during the winter/spring transition. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.