Microbial community dynamics in the forefield of glaciers

Abstract

Retreating ice fronts (as a result of a warming climate) expose large expanses of deglaciated forefield, which become colonized by microbes and plants. There has been increasing interest in characterizing the biogeochemical development of these ecosystems using a chronosequence approach. Prior to the establishment of plants, microbes use autochthonously produced and allochthonously delivered nutrients for growth. The microbial community composition is largely made up of heterotrophic microbes (both bacteria and fungi), autotrophic microbes and nitrogen-fixing diazotrophs. Microbial activity is thought to be responsible for the initial build-up of labile nutrient pools, facilitating the growth of higher order plant life in developed soils. However, it is unclear to what extent these ecosystems rely on external sources of nutrients such as ancient carbon pools and periodic nitrogen deposition. Furthermore, the seasonal variation of chronosequence dynamics and the effect of winter are largely unexplored. Modelling this ecosystem will provide a quantitative evaluation of the key processes and could guide the focus of future research. Year-round datasets combined with novel metagenomic techniques will help answer some of the pressing questions in this relatively new but rapidly expanding field, which is of growing interest in the context of future large-scale ice retreat.

Keywords: chronosequence; colonization; deglaciated forefield soils; microbial succession; modelling; nutrient cycling.

Figure 1.

Aerial photograph of the forefield of Midtre Lovénbreen, a retreating valley glacier in Svalbard. For scaling purposes, the proglacial lakes vary between roughly 40–100 m in length. Photo credit: J. Bradley.

Figure 2.

Pathways of nutrient cycling in a typical deglaciated forefield system.

Figure 3.

Accumulation of (a) total organic carbon and (b) total nitrogen in deglaciated forefield soils (see table 1 for source data).