Microbial Community and Biochemical Dynamics of Biological Soil Crusts across a Gradient of Surface Coverage in the Central Mojave Desert

Rakesh Mogul, Parag Vaishampayan, Mina Bashir, Chris P. McKay, Keith Schubert, Rosalba Bornaccorsi, Ernesto Gomez, Sneha Tharayil, Geoffrey Payton, Juliana Capra, Jessica Andaya, Leonard Bacon, Emily Bargoma, David Black, Katie Boos, Michaela Brant, Michael Chabot, Danny Chau, Jessica Cisneros, Geoff Chu, Jane Curnutt, Jessica DiMizio, Christian Engelbrecht, Caroline Gott, Raechel Harnoto, Ruben Hovanesian, Shane Johnson, Britne Lavergne, Gabriel Martinez, Paul Mans, Ernesto Morales, Alex Oei, Gary Peplow, Ryan Piaget, Nicole Ponce, Eduardo Renteria, Veronica Rodriguez, Joseph Rodriguez, Monica Santander, Khamille Sarmiento, Allison Scheppelmann, Gavin Schroter, Devan Sexton, Jenin Stephenson, Kristin Symer, Tatiane Russo-Tait, Bill Weigel, Mary B. Wilhelm

In this study, we expand upon the biogeography of biological soil crusts (BSCs) and provide molecular insights into the microbial community and biochemical dynamics along the vertical BSC column structure, and across a transect of increasing BSC surface coverage in the central Mojave Desert, CA, United States. Next generation sequencing reveals a bacterial community profile that is distinct among BSCs in the southwestern United States. Distribution of major phyla in the BSC topsoils included Cyanobacteria (33 ± 8%), Proteobacteria (26 ± 6%), and Chloroflexi (12 ± 4%), with Phormidium being the numerically dominant genus. Furthermore, BSC subsurfaces contained Proteobacteria (23 ± 5%), Actinobacteria (20 ± 5%), and Chloroflexi (18 ± 3%), with an unidentified genus from Chloroflexi (AKIW781, order) being numerically dominant. Across the transect, changes in distribution at the phylum (p < 0.0439) and genus (p < 0.006) levels, including multiple biochemical and geochemical trends (p < 0.05), positively correlated with increasing BSC surface coverage. This included increases in (a) Chloroflexi abundance, (b) abundance and diversity of Cyanobacteria, (b) OTU-level diversity in the topsoil, (c) OTU-level differentiation between the topsoil and subsurface, (d) intracellular ATP abundances and catalase activities, and (e) enrichments in clay, silt, and varying elements, including S, Mn, Co, As, and Pb, in the BSC topsoils. In sum, these studies suggest that BSCs from regions of differing surface coverage represent early successional stages, which exhibit increasing bacterial diversity, metabolic activities, and capacity to restructure the soil. Further, these trends suggest that BSC successional maturation and colonization across the transect are inhibited by metals/metalloids such as B, Ca, Ti, Mn, Co, Ni, Mo, and Pb.