Drylands cover about 46% of the global land surface, and more than 30% of their exposed soils are armored by biological soil crusts (biocrusts). Built by filamentous cyanobacteria, these delicate micro-ecosystems stabilize shifting sands, improve soil structure, and drive nutrient cycling — indispensable services in arid regions.

Inoculating cyanobacteria has emerged as a promising way to accelerate biocrust formation and restore degraded drylands. Yet the in situ mechanisms sustaining microbial biomass carbon (MBC) accumulation under seasonal environmental stress remain unclear.

A research team led by Prof. HU Chunxiang and Associate Prof. LI Hua, from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, now shows that stage-specific functional handoffs among cyanobacterial guilds, together with metabolic subsidies from heterotrophic partners — rather than the persistent activity of any single pioneer strain — underpin biocrust carbon accumulation.

This study was recently published in ISME Communications.

In an in situ experiment in the Hobq Desert, Inner Mongolia, the researchers inoculated shifting dunes with Konicacronema sp. (formerly Microcoleus sp.) and tracked circannual biocrust development via multi-omics profiling. Although the strain retained taxonomic dominance, metatranscriptomic and metaproteomic data exposed a striking functional handoff.

Microcoleus-like populations drove rapid initial formation through the oxidative pentose-phosphate pathway and enzymatic antioxidant systems, whereas Oscillatoria took over transcriptional dominance during harsher seasonal transitions via enhanced light harvesting, cyclic electron transport, and non-enzymatic photoprotection.

Genome-scale metabolic modeling further predicted that dominant cyanobacteria acted mainly as net importers, receiving amino acids, vitamins, cell-wall precursors, and phosphate from heterotrophic partners while supplying inorganic sulfur and iron–sulfur clusters. These syntrophic partnerships shifted from Microcoleus–Bacteroidetes during formation to Microcoleus–Myxococcota during seasonal transitions.

Piecewise structural equation modeling showed that solar radiation and soil salinity governed MBC indirectly, by shaping cyanobacterial composition and the balance between phototrophic assimilation and resource-acquisition strategies.

These findings reveal that biocrust carbon accumulation rests on temporal functional division among cyanobacterial guilds and heterotrophic subsidies, not on a single pioneer strain. This provides a trait-based blueprint for resilient synthetic inocula that combine Microcoleus-like pioneers, stress-tolerant Oscillatoria and Crinalium, and heterotrophic partners.

Field view of the study site, microscope photo of cyanobacterial inoculum, and close-up view of the biocrust layer. (Image by IHB)