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Antarctic Dry Valleys

Project Summary: Biogeochemistry of cyanobacterial mats and hyporheic zone microbes in McMurdo Dry Valley glacial melt water streams

Intellectual Merit

      Unique, but poorly characterized habitats of the Antarctic Dry Valleys are the seasonally wetted soils of the glacial melt-water streams. These streams  typically have extensive cyanobacterial mats which are a source of fixed C and N to the Valleys.  However, to date, no comprehensive biogeochemical/microbial biological studies exist on these systems.  We propose to study the interplay between the microbial mats in the ephemeral glacial streams and the microbiota of the hyporheic soils (wetted soil zone) underlying and adjacent to those mats. We hypothesize that these mats are important sources of organic carbon and fixed nitrogen for the soil communities of the hyporheic zone. Furthermore, we posit that because of dissolved organic carbon (DOC) and nitrogen (DON) release from mats, the hyporheic zone is a microbial oasis and a major source of fixed C and N for the entire Dry Valley ecosystem. Specifically, we will assess the importance of nitrogen and carbon fixation by the mats to the microbiota, the release of DOC, DON and inorganic nitrogen  and the response of the soil microbiota through this seasonally phased release.Our field efforts will entail both observational and experimental components. Direct comparisons will be made between the mats and microbial populations underlying rehydrated and desiccated mat areas, and between mat areas in the melt streams of the Adams and Miers Glaciers in Miers Valley. Both physiological and phylogenetic indicies of the soil microbiota will be examined. Observations will include estimates of rates of mat CO2 and N2 fixation, soil respiration and leucine uptake (protein synthesis) by soil bacteria, bacterial densities and population genetics. We will compare these parameters with data collected in adjacent dry soil areas. Ancillary data on dissolved inorganic and organic nutrient distributions will be collected. Experimental manipulations will include artificial rehydration of specific plots in year 1, and a stream diversion experiment in year two in order to detail the time course of response.

      This investigation seeks to integrate modern molecular genetic approaches (ARISA-DNA fingerprinting and ultra deep 16S rDNA microbial phylogenetic analysis) with geochemistry to study the diversity, ecology, and function of microbial communities that thrive in these extreme environments. Postulating how organisms adapt to these environments is important not only from a basic biological perspective, but has ramifications for early evolution and how life might exist on other planets where similar geochemical constraints exist. We have assembled a new interdisciplinary collaborative team that brings to this program expertise in microbial ecology, genomics, and biogeochemistry in extreme environments (Cary-Univ. of Delaware, Capone, USC, and Carpenter, SFSU)

      The aim of this project will be to characterize from a biogeochemical perspective a unique and potentially important ecosystem in the Dry Valleys, hyporheic soils, with regard to the structure of their microbial populations and the interactions among functional components of these systems.

      Broader Impacts: This project will provide research and educational opportunities for three graduate students at each of the three institutions involved. All of the PIs routinely involve undergraduates as work-study students and in REU programs. Furthermore, all three PIs participate in educational and outreach programs.