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.

中文翻译：

---

高北极生物结皮：胞外多糖基质的表征

生物结皮可以在广泛的栖息地中找到，在那里它们提供重要的生态系统服务。这些微生物关联在高北极环境中尤为重要，在那里生物结皮在冰川退缩后定居在新暴露的贫瘠土壤中，并显着促进土壤稳定和养分循环。从初期的、结构简单的生物层开始，它们变得复杂，从冰川末端开始增加。从一个简单的群落结构开始，主要由蓝藻、异养细菌和真菌组成，它们沉浸在自分泌的细胞外聚合物基质（蓝藻结皮）中，然后它们可能会招募苔藓和地衣（分别为苔藓结皮和地衣结皮）。细胞外聚合物基质保护生物地壳群落免受非生物约束，尤其是干旱和冰冻压力、外部物理伤害因素和捕食。细胞外基质的理化特性与其若干特性有关，例如其土壤稳定作用和保水作用。我们分析了在挪威斯匹次卑尔根西北部收集的具有不同形态的生物结壳的细胞外聚合物基质的化学（单糖组成）和大分子（分子量分布）特性。细胞外多糖基质 (EPM) 的糖醛酸含量和分子量 (MW) 分布与生物壳的发育阶段一致。MW 分布也显示出样品之间的显着差异，这可能反映了微生物酶活性的差异，导致高分子量聚合物降解为更小的化合物。MW 分布图呈现出一些重要的差异，反映了环境条件的差异，可能还反映了微生物群落组成的季节性变化，已知该变化表征了本研究中检查的环境。