Change of the active bacteria mediating HCO₃ ^--fixation in biological soil crusts using DNA-based stable isotope...

Biological soil crusts (BSCs) are important primary producers in drylands. Autotrophs therein are typically dormant in dry seasons and revive in wet seasons. However, active members of dissolved bicarbonate after revival remain underexplored. Here, H¹³CO₃ ^- was used to determine the active carbon-fixers in BSCs and underlying soils in the resuscitation (RP, 0-7 days) and sustained hydration (SHP, 7-14 days) phases. In the SHP, BSCs had higher nutrient levels and biomass than in the RP. Blastococcus mobilis, Modestobacter altitudinis, Scytonema hyalinum, and some unclassified strains were identified as HCO₃ ^--fixers based on DNA stable isotope probing (DNA-SIP). Precisely, photoautotrophs and chemoautotrophs were the main HCO₃ ^--fixers of BSCs in the RP and SHP, respectively. Additionally, ¹³C-transformers were enriched in the underlying soils and related to nutrient cross-feeding. Our findings unveiled bacterial HCO₃ ^--fixers and their dynamics in BSCs reviving from dormancy, providing clues for the mechanisms of inorganic carbon-fixation in drylands.