Cyanobacteria and loess—an underestimated interaction

Background Biocrusts are important functional units in dryland ecosystems. Regarded as ecosystem engineers, cyanobacteria in biocrusts contribute several major physico-chemical and biological processes. However, the role of cyanobacteria in the process of loess formation has been underestimated. Recently, their contribution to sediment development was presented in the BLOCDUST model of loess formation.

Scope This perspective paper features the environmental impact of cyanobacteria and biocrusts with a focus on processes involved in the formation of loess sediments. We propose that the formation of loess can be mediated by cyanobacteria, including initial trapping, and the accumulation and preservation of loess-forming particles. Moreover, the initial structure may be further altered by weak mineral weathering, dissolution and mineral re-precipitation due to cyanobacterial metabolic processes. Possible negative aspects of environmental impact related to the potential toxicity of cyanobacterial biocrusts are also discussed. We highlight specific biotic-abiotic interactions between biocrusts and loess (e.g. exudation of organic polymers, carbonate dissolution and re-precipitation, and dust-dependent metabolic activities of cyanobacteria) which are essential for the formation of stabilized loess and propose the term “synergosis” to comprise these interactions. 

Conclusion The role of cyanobacteria in loess formation has only recently been recognized and the possible biogenic nature of loessification is underestimated as compared to their eolian nature. Mineral weathering and mineral precipitation processes as well as mineral dust flux between litho- and atmosphere mediated by cyanobacteria and biocrusts require more attention due to their significant contribution to ecosystem properties.