High Arctic biocrusts: characterization of the exopolysaccharidic matrix

Abstract

Biocrusts can be found in a wide array of habitats, where they provide important ecosystem services. These microbial associations are particularly important in High Arctic environments, where biocrust colonize the newly exposed barren soil after glacier retreat and significantly contribute to soil stabilization and nutrient cycling. Starting from incipient, structurally simple biolayers, they develop in complexity, increasing from the glacier terminus. Starting from a simple community structure, mainly constituted by cyanobacteria, heterotrophic bacteria and fungi immersed in a self-secreted extracellular polymeric matrix (cyanobacterial crusts), they later may recruit mosses and lichens (moss crusts and lichen crusts, respectively). The extracellular polymeric matrix protects the biocrust community from abiotic constraints, notably drought and freezing stress, from external physical harming factors, and from predation. The physicochemical characteristics of the extracellular matrix are related to several of its properties, such as its soil-stabilizing effect and water retention. We analysed the chemical (monosaccharidic composition) and macromolecular (molecular weight distribution) properties of the extracellular polymeric matrix of biocrusts with different morphologies collected in northwestern Spitsbergen, Norway. The uronic acid content and molecular weight (MW) distribution of the extracellular polysaccharidic matrices (EPMs) appeared in accordance with the developmental stages of the biocrusts. The MW distribution also showed significant differences between the samples, possibly reflecting differences in microbial enzymatic activities leading to the degradation of high-MW polymers into smaller compounds. The MW distribution profiles presented some important differences, reflecting differences in environmental conditions and, probably, the seasonal variance in microbial community composition that is known to characterize the environment examined in the present study.

Environmental micro‐niche filtering shapes bacterial pioneer communities during primary colonization of a Himalayas' glacier forefield

“…A similar trend of biomass and nutrients accumulation within the crust surface rather than in the bare soil was observed along an elevation gradient from 5300 to 5900 m asl in the Tibetan plateau (Chu et al, 2016;Janatkov a et al, 2013). NMR analysis of BSCs revealed the load of O-alkyl, alkyl and N-alkyl carbon, indicating that the input of carbon derived from the biocrust comprises polysaccharides and aliphatic biopolymers, in agreement with the BSC-produced extracellular polymeric substances (Mugnai et al, 2020;Rossi et al, 2018). Carbon transfer from the biocrusts to the substrate below was mainly observed in temperate conditions for well-developed BSC like those moss-dominated (Dümig et al, 2012).…”

The role of biocrust-induced exopolymeric matrix in runoff generation in arid and semiarid zones – a mini review

“…Thus for instance, while sulfated groups and uronic acids are hydrophilic (Rossi and De Philippis, 2016), their presence cannot fully explain water absorption by the crust. For example, while young cyanobacterial crusts were found to only posses low amounts of uronic acids (Mugnai et al, 2020b), young cyanobacterial crusts were still observed to readily absorb water during a sprinkling experiment, and subsequently to generate runoff (Kidron, 2015). Nevertheless, it is believed that water absorbance may vary in accordance with the EPS properties (Chenu, 1993).…”