Functional shifts in unvegetated, perhumid, recently-deglaciated soils do not correlate with shifts in soil bacterial community composition

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 approximately 0.14 mg/g soil, soil organic carbon pools ranged from 0.6 approximately 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 approximately 5 ng N fixed/cm(2)/h, a trend that was matched by the activity of the soil N-cycling enzymes urease and beta-l,4-N-acetyl-glucosa-minidase. 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.

Bacterial community structure on two alpine debris-covered glaciers and biogeography of Polaromonas phylotypes

“…This interpretation is corroborated by the observations that distance from the terminus is represented by a vector opposite to those representing the other two variables in the redundancy analysis plot (Figure 3). The results from the multivariate analysis therefore suggest that glacier debris cover may host chronosequences similar to those observed in glacier forefields Nicol et al, 2005;Nemergut et al, 2007;Schmidt et al, 2008;Sattin et al, 2009;Schutte et al, 2009Schutte et al, , 2010Philippot et al, 2011;Knelman et al, 2012;Zumsteg et al, 2012).…”

“…Particularly, some works suggested that Cyanobacteria are important sources of C in very early succession stages and some surveys did report high abundances of Cyanobacteria in early colonization stages (Nemergut et al, 2007;Schmidt et al, 2008;Zumsteg et al, 2012). On the contrary, other investigations showed low abundances of Cyanobacteria in glacier forefields without any relation between their abundance and soil age Sattin et al, 2009;Goransson et al, 2011;Knelman et al, 2012). Hence, the role of Cyanobacteria in the very early stages of ecosystem development is currently controversial.…”

“…Indeed, in Alpine environments, microbial succession studies have typically been conducted only on glacial forefields, where the distance from the receding glacier front served as a proxy for time since organism colonization Nicol et al, 2005;Nemergut et al, 2007;Schmidt et al, 2008;Sattin et al, 2009;Schutte et al, 2009Schutte et al, , 2010Philippot et al, 2011).…”

Culturable bacteria community development in postglacial soils of Ecology Glacier, King George Island, Antarctica

“…Total and photoautotrophic cell counts followed this trend, reaching a maximum in well-formed soils in Zone III. Sattin et al (2009) describe a similar observation based on clone libraries during their work on Mendenhall Glacier foreland soils (USA). Counts at sampling points E2 and F2 could have been influenced by significant numbers of edaphic ciliates which control bacterial populations (Mieczan, unpublished).…”

Changes in assembly processes in soil bacterial communities following a wildfire disturbance

“…For instance, spore-forming Firmicutes -which may be more easily dispersed-are most abundant in the 4 week postburn soils. As well, Betaproteobacteria, which commonly dominate early successional landscapes Sattin et al, 2009) are more abundant at 16 weeks, when the decrease in soil organic matter (Table 1) may select for more oligotrophic taxa. We performed Mantel tests to examine correlations between environmental parameters and community structure.…”