PARENT SESSION
Oral Session # 35: Biogeochemistry III: Arctic, Alpine, and Tundra Systems.
Presiding: A Hartley
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 203.
Dissolved organic carbon in soils, streams, and lakes of an arctic catchment: linking bioavailability, chemistry, and microbial community comoposition.
Judd, Kristin*,1, Crump, Byron2, Zak, Don1, Sinsabaugh, Robert3, Kling, George1, 1 University of Michigan, Ann Arbor, MI2 Ecosystem Center, Marine Biological Lab, Woods Hole, MA3 University of New Mexico, Albuquerque, NM
ABSTRACT- The transport rate and processing of dissolved organic carbon (DOC) through catchments depends, in part, on its bioavailability to the microbes it encounters as it travels down-slope. DOC chemical characteristics and microbial community physiological capabilities determine DOC bioavailability; however, little is known about the relative importance of these factors at various locations in a catchment or over the course of the growing season. To better understand the major controls on spatial and temporal patterns of DOC bioavailability and microbial activity, we examined microbial community composition and DOC chemistry along a terrestrial-aquatic gradient in an arctic catchment and conducted experiments to determine the relative importance of these two factors in controlling carbon processing. Both DOC chemistry and microbial community structure (phospholipid fatty acids) differed between tussock, birch-willow, and wet sedge soils. In mesocosm experiments, we simulated down-slope transport of DOC by adding DOC from up-slope soil and surface water sources to stream and lake microbial communities. Microbial production was monitored over the course of four weeks, and DOC chemistry (phenolics, simple carbohydrates, and amino acids) and microbial community composition (denaturing gradient gel electrophoresis (DGGE)) was measured at the beginning and end of the experiment. Addition of up-slope DOC altered microbial production such that it was similar to microbial production of DOC source communities. Addition of both wet sedge and tussock soil-water DOC to stream and lake microbial communities greatly enhanced microbial production relative to controls. Addition of stream water to a lake inoculum, however, depressed microbial production in lake water communities. Over the course of the experiment, microbial community structure in treatment mesocosms shifted in the direction of the DOC source community, and the addition of soil-water DOC had the strongest effect. These results suggest that DOC chemistry strongly drives the structure and function of microbial communities in arctic tundra systems.
Key words: bioavailability, microbial community composition, dissolved organic carbon