Halophilic Algal Communities in Biological Soil Crusts Isolated From Potash Tailings Pile Areas

Abstract

Mining potash for fertilizer produces vast amounts of highly saline waste that is deposited in potash tailings piles. Rainfall washes the salts out, affecting the surrounding ecosystems. Only salt-tolerant organisms occur close to the piles, since other species cannot survive in these hypersaline conditions. Halophytic plant communities around tailings piles have been well investigated. However, studies exploring the biodiversity of the space behind the vegetation line that separates suitable salinities for plant growth from hostile conditions are rare. On top of the tailings piles, only microorganisms thrive. This study, for the first time, explored the microalgae and cyanobacteria in biocrusts that inhabit potash tailings pile areas between the vegetation line and the pile body. Two biocrust types were studied: young biocrusts at or close to the tailings piles, and established biocrusts situated in the near surroundings. The estimated abundance of green algae, cyanobacteria and diatoms was studied using a direct microscopy approach, followed by the isolation and establishment of unialgal strains and morphological species determinations. Soil environmental characteristics were analyzed. Soil samples showed EC Sat (electrical conductivity) values that drastically exceeded the scales commonly used to describe soil salinity, indicating extremely saline conditions. Indeed, the isolate composition was shaped by soil salinity parameters. Soil EC Sat of young biocrusts tended to be higher than in established biocrusts, and filamentous green algae were most abundant. In contrast, established biocrusts tended to have a lower EC Sat and were mostly dominated by filamentous cyanobacteria. Algal and cyanobacteria isolate composition differed significantly in young and established biocrusts, although the species number did not. Some of the salt-tolerant algal strains are assumed to be candidates for the formation of artificial biocrusts on the surface of the tailings. Attempts to "green" the piles by the establishment of higher plants to trap rainwater and therefore reduce the salt-output are difficult to apply. Plants require a thick layer of substrate to reduce the salinity, and the substrate easily erodes on the steep slopes. However, microalgae isolated from potash tailings pile areas seem promising, since they can survive on a thinner substrate layer and are already adapted to these hypersaline conditions.

Diversity of Microorganisms in Biocrusts Surrounding Highly Saline Potash Tailing Piles in Germany

“…The phylum Chlorophyta, with the dominance of the two families (Chlorophyceae and Trebouxiophyceae), was the only representative of the clade. These eukaryotic microalgae are typically found in biocrusts [ 42 ] and were also reported in the studied potash tailing piles [ 17 , 18 ]. They produce organic osmolytes, which serve as salt protectants [ 43 ], and extracellular polymeric substances (EPS) that provide several functions including drought tolerance [ 44 ], which, in turn, might have a salt-buffering effect.…”

“…A total of twelve highly saline biocrust samples from the areas surrounding five potash tailings piles in Germany (Shreyahn (SY), Oedesse (OD), Wietze (WT), Teutschenthal (TT), the not named site (NN)) were used in this study. Site descriptions and sampling as well as the chemical parameters and microphototrophic community composition were presented in two previous publications [ 17 , 18 ] and are summarised in Supplementary Table S1 .…”

“…Various studies have addressed the occurrence of microbial phototrophs [ 7 ], fungi [ 8 , 9 , 10 ] and bacteria as well as Archaea [ 11 , 12 , 13 , 14 ] in hypersaline environments alone. However, microbial community composition in biocrusts from naturally saline habitats was described in a few studies only [ 15 , 16 ] and that of German potash tailing piles exclusively by Sommer et al [ 17 , 18 ]. Besides, both latter studies, using traditional culture-dependent methods, showed a diverse community of microbial phototrophs in the biocrusts [ 17 , 18 ].…”

“…However, microbial community composition in biocrusts from naturally saline habitats was described in a few studies only [ 15 , 16 ] and that of German potash tailing piles exclusively by Sommer et al [ 17 , 18 ]. Besides, both latter studies, using traditional culture-dependent methods, showed a diverse community of microbial phototrophs in the biocrusts [ 17 , 18 ].…”

“…Therefore, it is crucial to understand the impact of salt on biocrust microbiota inhabiting the surroundings. Here, we applied high-throughput sequencing (HTS) to obtain thorough and comprehensive insight into biocrust microbial community composition, with an emphasis on bacteria, cyanobacteria, fungi and other eukaryotes in the previously partially described biocrusts [ 17 , 18 ]. These data will help us to better understand the presence and abundance of specific salt-tolerant microorganisms in anthropogenically disturbed mining areas.…”