As greenhouse effects rise, soil carbon has been a major focus of research on climate change. Soil microorganisms are the key groups that drive soil carbon transformation. Due to the complexity of factors such as microbial physiology, the composition of organic compounds in soils, and the variation among redox forms, the pattern and process of soil carbon cycle at the microbial community level can be difficult to study.
Biocrusts are ideal for modeling when it comes to large distribution in arid regions, which account for > 40% of the global land surface, and cryptophytes like Cyanobacteria, lichens, and mosses. These nutrients are capable of preventing wind erosion of sandy soils, thus promoting ecosystem development and succession.
A research team led by Prof. HU Chunxiang of the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences studied the community-based carbon cycle overall patterns and successional variation in biocrusts, as well as the relationships between C-cycle processes, environmental variables, and microorganism groups.
In order to accomplish this, researchers used four types of biocrusts that represent different successional stages, i.e., cyanobacteria-dominated crusts, A; cyanolichen-dominated crusts, C; chlorolichen-dominated crusts, G; and moss-dominated crusts, M. These were collected once in the Shapotou district in the Tengger Desert in the past four years.
Metagenomic sequencing produced a low amount of genes that related to light-driven inorganic carbon fixation and a high level of genes that related to macromolecular organic carbon degradation (OC), fermentation, aerobic respiration, and CO oxidation.
Genes that mediate starch/glycogen and cellulose degradation were most abundant during the initial complex OC degradation, as were genes that mediated fermentation during the final stages of OC decomposition, according to Prof. HU.
The researchers combined metagenomic data with absolute quantification via GeoChip and key enzyme activity measurements. Observations showed that inorganic carbon fixation, fermentation, CH4oxidation, and both starch/glycogen and peptidoglycan degradation decreased during succession, whereas several high-efficiency processes, as well as CO oxidation and most kinds of OC degradation, increased.
In addition, researchers identified that the C-cycle in biocrusts includes an assimilation module, comparable to primary production, and a dissimilation module, which is also comparable to secondary production. Moreover, they found that dynamic changes in the relationship between C-cycle pathways and microbial community composition were made during succession. The two C-cycle modules were linked by the Calvin-Benson cycle, ethanol, and propionate fermentation, and they were balanced by drought and salinity.
This study further enriched the understanding of C-cycle pathways and regulatory mechanisms in biocrust succession, and paved the groundwork for future multi-omics investigations of these systems.