Soil type and precipitation level have a greater influence on fungal than bacterial diversity in serpentine and non-serpentine biological soil crusts

Serpentine soils are characterized by nutrient imbalances and high levels of potentially toxic metals (PTMs). These soils host depauperate plant communities of species with specialized adaptations. Initial studies showed that South African serpentine soils harbor distinct biocrust algal and cyanobacterial species compared to adjacent non-serpentine soils, with these communities further differing based on high and low precipitation levels. Here, we investigated the bacterial and fungal diversity of biological soil crusts from serpentine and non-serpentine soils at two precipitation levels. The bacterial and fungal communities were characterized using 16S rDNA and ITS metabarcoding, respectively. No significant differences could be found in bacterial richness and community structure. Nevertheless, bacterial taxa such as Archangium, Candidatus Solibacter, Chthoniobacter, and Microvirga were more abundant in serpentine biocrusts or biocrusts receiving lower precipitation. The fungal community structure was distinct between serpentine and non-serpentine soils (p = 0.027) and between high and low precipitation (p = 0.018). Furthermore, fungal diversity was lowest in the drier, serpentine biocrusts compared to non-serpentine (p = 0.001) and serpentine crusts receiving higher precipitation (p = 0.002). The fungal genera, Ramimonilia and Vishniacozyma, which are known to be resistant or tolerant to PTMs and other environmental extremes, were significantly more abundant (p = 0.036 and p = 0.016, respectively) in serpentine biocrusts, with the latter indicating serpentine habitats. This study concluded that soil type influenced the fungal alpha diversity, specifically in the serpentine soil, resulting in a decrease in fungal species richness. Furthermore, precipitation influenced fungal beta diversity by shaping distinct fungal communities found in the biocrusts of serpentine and non-serpentine soils.