The carbon cycle of the microbial community studied in biological crusts

As greenhouse effects become more visible, soil carbon is a major focus of research on climate change. Soil microorganisms are the key groups that stimulate the transformation of carbon in the soil. Due to the complexity of factors such as microbial physiology, the composition of organic compounds in soils and variations between redox forms, the model and process of the soil carbon cycle at the microbial community level can be difficult to study using metagenomics.

For studies of soil ecosystems using metagenomics, biocortexes are ideal for modeling because they are widespread in dry regions, represent> 40% of the global earth’s surface, and are dominated by cryptophytes such as cyanobacteria, lichens, and mosses. They can also prevent wind erosion of sandy soils, thus promoting the development and coherence of ecosystems.

In a study published online in Soil biology and biochemistryA research team led by Prof. HU Chunxiang of the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences examines common carbon cycle models in the community and successive variations in biocortex, as well as the relationships between C-cycle processes, environmental variables and groups of microorganisms.

To achieve this, the researchers used four types of biocortexes, which represent different successive stages, ie. cyanobacterial-dominated barks, A; dominated by cyanolic lichens, C; dominated by chlorolichen crusts, G; and dominated by moss bark, M. They have been collected repeatedly from the Shapotu region of the Tenger Desert over the past four years.

Researchers first observed a small abundance of genes associated with light-driven fixation of inorganic carbon, and a large abundance of genes associated with the chemical energy degradation of macromolecular organic carbon (OC), fermentation, aerobic respiration, and oxidation of CO by metagenomic sequencing. .

“For OC degradation, we found that the genes that mediate the breakdown of starch / glycogen and cellulose are most abundant during the initial degradation of the OC complex, as well as the genes that mediate fermentation during the terminal stages of OC degradation,” he said. Prof. HU.

To assess successive changes in the carbon cycle, TIn addition, the researchers combined metagenomic data with absolute quantification by GeoChip and key measurements of enzyme activity. “We observed that the fixation of inorganic carbon, fermentation, CH4 Oxidation and degradation of both starch / glycogen and peptidoglycan decreases during the sequence, while several highly efficient processes, as well as CO oxidation and most types of OC degradation, increase, ”said HU.

In addition, using cogeneration networks, the researchers found that the C-cycle in biocortexes includes an assimilation module similar to primary production and a dissimilation module comparable to secondary production. They also found that dynamic changes in the relationship between C-cycle pathways and microbial community composition occurred during the sequence. “The two modules of the C-cycle were linked by the Calvin-Benson-Basham cycle, ethanol and propionate fermentation and were balanced by drought and salinity,” explained HU.

This study improved the understanding of C-cycle pathways and regulatory mechanisms in the biocortical sequence and laid the groundwork for future multi-ohmic studies of these systems.

reference: Wang Q, Zhang Q, Han Y, Zhang D, Zhang CC, Hu C. Carbon cycle in microbial ecosystems of biological soil crusts. Soil Biol Biochem. 2022; 171: 108729. doi: 10.1016 / j.soilbio.2022.108729

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