Morphology and distribution of biological soil crusts and their potential role in soil-forming processes under dry high-altitude periglacial conditions (Eastern Pamir, Tajikistan)

Abstract

Under demanding climatic conditions that limit the development of vascular vegetation, biological soil crusts (BSCs) drive the processes of soil formation and nutrient sequestration. Though BSCs were studied in glacier forelands worldwide, the high-altitude areas with a combination of glaciation/deglaciation and arid or hyperarid climate remain almost unstudied in this respect. Therefore, we provided the first data on BSCs from a glacier foreland in the E Pamir. These characteristics can be crucial for assessing BSC's role in soil-forming processes in dry, high-altitude periglacial environments. During our research, we assessed (1) BSCs’ morphology and distribution; (2) microbial biomass and nutrient retention patterns in morphologically differentiated BSC types, (3) C, N and P accumulation in BSCs biomass in comparison to sub-crust soils; (4) sub-crust soils enrichment in C, N and P in comparison to bare soils and soils under vascular plants; (5) potential origin and transformation degree of organic matter accumulated by BSCs. Our study showed that the distribution and development of BSCs were noticeably restricted, probably due to low temperatures, aridity and intense periglacial processes, resulting in continuous soil surface remodeling. Thus, poorly developed BSCs were the dominating biologically active soil cover type and, thus, most likely the main biological soil-forming factor in the foreland. BSCs accumulated C, N and P in their biomass and enriched their sub-crust soils in these nutrients. The average enrichment observed for soils under advanced crusts was similar to those obtained for soils under vascular plants. In all types of the studied samples, including bare soils, n-alkanes of vascular plant origin dominated, indicating mixing and uniform distribution of organic matter. Over the course of aridification projected for the Pamir Mountains, the BSCs could potentially become the most important player in the accumulation of soil nutrients in this area. However, due to the dominance of the simplest BSC type, soil formation in the Uisu Glacier foreland will be relatively slow.