Title Functional Shifts in Unvegetated, Perhumid, Recently-Deglaciated Soils Do Not Correlate with Shifts in Soil Bacterial Community Composition
Author Sarah R. Sattin1,2, Cory C. Cleveland3, Eran Hood4, Sasha C. Reed3, Andrew J. King1, Steven K. Schmidt1, Michael S. Robeson1, Nataly Ascarrunz1,2, and Diana R. Nemergut2,5*
Address 1Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309, USA, 2Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA, 3Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, Montana 59812, USA, 4Environmental Sciences Program, University of Alaska Southeast, Juneau, Alaska 99801, USA, 5Environmental Studies Program, University of Colorado, Boulder, Colorado 80309, USA
Bibliography Journal of Microbiology, 47(6),673-681, 2009,
Key Words N fixation, microbial community structure, succession, soil enzyme activity
Abstract Past work in recently deglaciated soils demonstrates that microbial communities undergo shifts prior to plant colonization. To date, most studies have focused on relatively ‘long’ chronosequences with the ability to sample plant-free sites over at least 50 years of development. However, some recently deglaciated soils feature rapid plant colonization and questions remain about the relative rate of change in the microbial community in the unvegetated soils of these chronosequences. Thus, we investigated the forelands of the Mendenhall Glacier near Juneau, AK, USA, where plants rapidly establish. We collected unvegetated samples representing soils that had been ice-free for 0, 1, 4, and 8 years. Total nitrogen (N) ranged from 0.00~0.14 mg/g soil, soil organic carbon pools ranged from 0.6~2.3 mg/g soil, and both decreased in concentration between the 0 and 4 yr soils. Biologically available phosphorus (P) and pH underwent similar dynamics. However, both pH and available P increased in the 8 yr soils. Nitrogen fixation was nearly undetectable in the most recently exposed soils, and increased in the 8 yr soils to ~5 ng N fixed/cm2/h, a trend that was matched by the activity of the soil N-cycling enzymes urease and β-1,4-N-acetyl-glucosaminidase. 16S rRNA gene clone libraries revealed no significant differences between the 0 and 8 yr soils; however, 8 yr soils featured the presence of cyanobacteria, a division wholly absent from the 0 yr soils. Taken together, our results suggest that microbes are consuming allochtonous organic matter sources in the most recently exposed soils. Once this carbon source is depleted, a competitive advantage may be ceded to microbes not reliant on in situ nutrient sources.