Functional Shifts in Unvegetated, Perhumid, Recently-Deglaciated Soils Do Not Correlate with Shifts in Soil Bacterial Community Composition

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 o f development. However, some recently deglaciated soils feature rapid plant colonization and questions remain about the relative rate o f 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 con centration 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 un detectable in the most recently exposed soils, and increased in the 8 yr soils to-5 ng N fixed/cm /h, a trend that was matched by the activity o f the soil N-cycling enzymes urease and p-l,4-N-acetyl-glucosa-minidase. 16S rRNA gene clone libraries revealed no significant differences between the 0 and 8 yr soils