Serpentine Biocrust Microbes Maintain Nitrogen Cycling Under Drought and Heavy Metal Stress

ABSTRACT

Biocrusts play an important role in nitrogen cycling in terrestrial ecosystems. However, little is known about how environmental and climatic factors influence microbial community composition and the functional genetic potential. We used shotgun metagenomic sequencing to compare species diversity and genetic potential for nitrogen cycling in biocrust microbiomes under wetter and drier moisture regimes in serpentine and nonserpentine soils in South Africa's Barberton Greenstone Belt. Microbial community structure, composition, and gene profiles varied in response to both soil type and moisture regime. Although no statistically significant differences were detected among sites, site‐specific trends showed that Actinobacteria had higher mean relative abundances in drier serpentine crusts. Proteobacteria and Nitrospirae showed higher mean relative abundances in drier nonserpentine crusts, and Cyanobacteria were more abundant in wetter nonserpentine crusts. Similarly, variation in mean relative abundance across sites showed that the ure C gene was the most abundant gene involved in nitrogen cycling, although it was less abundant in serpentine samples, which may reflect constraints associated with higher metal concentrations in serpentine soils. Cyanobacteria associated with nitrogen fixation showed higher mean relative abundances in wetter nonserpentine samples. In contrast, nitrifying archaea had higher relative abundances in the drier samples. Overall, our results suggest that nitrogen‐cycling microbial communities in biocrusts may respond to both soil geochemistry and moisture regime, although many of the observed differences were not statistically significant. This highlights the ecological importance of biocrusts in regulating nitrogen availability in serpentine and nonserpentine ecosystems.