Soil phototroph community resilience comes from down under

Brian ScottFerran Garcia-Pichel^*

• Arizona State University, Tempe, United States

Seed banks are widely recognized as means of recovery following disturbance across diverse ecosystems, including soil. Phototrophic microbes, while common in surface soils, have not been considered within this context. We found evidence of phototroph seed banking by studying biological soil crusts (biocrusts), which form conspicuous and ecologically important communities structured around cyanobacteria in drylands. Biocrusts comprise a millimeters-thin cohesive surface layer resting atop a looser, often overlooked, undercrust (the layers of desert soil proximal to, but below the distinct, cohesive biocrust layer). To investigate community resilience, we subjected a variety of biocrusts to severe disturbance by scalping off the surface layer, thereby exposing the undercrust. Molecular and pigment analyses revealed consistently rapid recovery originating from the undercrusts, which harbored vanishingly small but phylogenetically diverse populations of viable, dormant cyanobacteria, effectively functioning as microbial seed banks. Alternative pathways for recovery, including natural or interventional inoculation and lateral spread, did not constitute a comparable force. Our findings bring soil phototrophs within the ecological framework linking seed banks to resilience following disturbance. The overlooked role of undercrusts in prior research invites a reinterpretation of past studies and may inform new restoration strategies.