Microbial Diversity and Activity along the Forefields of Two Receding Glaciers

Abstract

Forefields of two receding glaciers were sampled along either a 150 or 200 m long transect at identical spatial intervals for assessment of soil microbial activity and community diversity trends. The forefields belonged to the Dammaglacier (forefield area is 157 ha, 2000 m above sea level) and Rotfirnglacier (100 ha, 2200 m) and at the time of sampling were receding at an estimated rate of 8 and 10 m yr(-1) over the past 5 years, respectively. Direct counting of bacteria (DAPI staining), assessment of dehydrogenase activity (DH), and fluorescein diacetate hydrolysis activity (FDA) were performed to estimate bacteria number and soil microbial activity. Along the Dammaglacier forefield (from youngest to oldest soil), bacteria number (8.21 x 10(7) to 1.49 x 10(9) cells g(-1) soil), DH activity (0 to 61 mg TTC reduced g(-1) soil h(-1)), and FDA activity (0 to 100 mg fluorescein produced g-1 soil h-1) increased, suggesting the development of microbial populations increasing in number and activity. The Rotfirn forefield exhibited similar trends per gram of soil in bacteria number (1.13 x 10(8) to 5.93 x 10(9) cells), DH activity (0 to 36 mg TTC reduced), and FDA activity (2 to 70 mg fluorescein produced), but with more variability among samples than the Damma forefield samples. Molecular assessment of bacterial diversity included denaturing gradient gel electrophoresis (DGGE) and ribosomal intergenic spacer analysis (RISA) of soil DNA. DGGE and RISA revealed that the composition and succession of bacterial populations were different in both forefields. Comparison of Shannon diversity index values indicated that all populations sampled from the Damma forefield were significantly different (p < 0.05). Conversely, similar populations existed in the Rotfirn forefield succession. Overall, the results indicate that diverse bacterial assemblages increasing in number and activity characterize these glacier forefield soils with both forefield successions exhibiting differing modes of bacterial community establishment.

Bacterial Communities Involved in Soil Formation and Plant Establishment Triggered by Pyrite Bioweathering on Arctic Moraines

“…1). Young deglaciated moraines were reported to host unsuspected high bacterial diversity, probably due to a loss of competition in poorly developed environments [11], where fungal mycelia and plant roots are hampered by nutrient limitations and mechanical constrains like freeze and thaw cycles [21,22]. On the contrary, in developed soils, high diversity in substrate sources and interactions with plants and microfauna lead to high bacterial diversity indexes [23,24].…”

“…Very few works nevertheless analytically described the microbial succession along glacier forefronts. Successions of communities of early colonizers, dominated by Cyanobacteria, followed by typical soil bacterial phylotypes have been described, occurring in a large time interval during glacial regression in several glacier forefronts [8][9][10][11][12].…”

The role of microorganisms at different stages of ecosystem development for soil formation

“…This includes increasing amounts of organic C and N, the formation of soil horizons, increasing microbial biomass and enzyme activities even in the bulk soil (Dümig et al, 2011;Brankatschk et al, 2011;Duc et al, 2009;Sigler and Zeyer, 2002). Once a stable plant community has developed, a positive feedback loop establishes.…”

Soil Bacterial and Fungal Communities Show Distinct Recovery Patterns during Forest Ecosystem Restoration

“…However, reported patterns in chronosequences are not easily generalized. For example, microbial diversity has not shown consistent patterns in glacial chronosequences (26)(27)(28)(29), and an abundance of bacterial phyla showed different trends along chronosequence ages in two glacier forelands within the same study (30). These differences have been attributed to heterogeneity of physical landforms, soil structure, environmental conditions, and vegetation across those gradients (31).…”