Soil organic carbon (SOC) pool is larger than the combined carbon stock in the vegetation and atmosphere (Davidson et al., 2000; Schmidt et al., 2011; Scharlemann et al., 2014). Carbon (C) exchange between soil and the atmosphere is crucial for the terrestrial C cycle. Soil microbes regulate soil C dynamics through the transformation of plant-derived C, assimilation of C resources to build up their biomass and necromass, decomposition of soil organic matter, and CO2 release. The intensities and efficiencies of these processes are critical determinants of net ecosystem C storage and CO2 fluxes (Buckeridge et al., 2022; Camenzind et al., 2023; Chen et al., 2023; Tao et al., 2023; van Bruggen et al., 2017; Wang et al., 2021). Although there is continuing and growing interest in elucidating the underlying microbial mechanisms driving soil C transformation, stabilization, and release processes, there are still many challenges in manipulating the soil microbial communities for C storage. For example, identifying major players in C storage and decomposition, determining the genetic basis of the mechanisms involved in C sequestration, understanding complex interactions between soil physico-chemical properties, plants, and microorganisms over large spatial and temporal scales, and incorporating microbial community patterns and process rates into ecosystem models (Barnett et al., 2023; Li et al., 2021; Wu et al., 2023; Yang et al., 2022).
This Research Topic aimed to increase our understanding of the role of microorganisms in soil organic C storage and mobilization processes, as well as to improve our capabilities to develop and evaluate cost-effective microbial strategies for C sequestration and mitigating anthropogenic CO2 emissions, ultimately assisting to achieve the goals of C neutrality and CO2 peaks. Altogether, 11 articles published within the framework of this Research Topic cover a broad range of the processes of C cycling. Most studies have attempted to link plant communities, organic matter properties, and the soil microbiome. Liu et al. examined the characteristics of nutrient release and microbial diversity structure during the decomposition of three types of litter in arid and semi-arid regions. They revealed that the nutrient content and the rate of decomposition of mixed litter strongly increased compared to litter of single species. This is because litter mixing raised the richness and diversity of the microbial communities. Based on original soil microcosm with decomposing corn and soy leaves, as well as soil adjacent to the leaves, Benucci et al. concluded that microbial composition was primarily affected by spatial niches, but also by soil management type and plant species in the fungal microbiome. Moisture content and pore sizes, however, were most important drivers for bacterial communities. Guo et al. evaluated the impact of natural vegetation restoration on soil physical and chemical properties as well as microbial community diversity and composition in the alkaline-saline soils of the Songnen Plain, China. Leymus chinensis and Phragmites australis grown under these harsh conditions increased SOC content and microbial diversity. Analyzing the spatial variability of soil respiration (RS) and its drivers in the Northwest Caucasus Mountains, Russia, in mixed, fir, and deciduous forests, as well as subalpine and alpine meadows, Sushko et al. concluded that microbial activity played a crucial role in RS spatial variability in forests. Composition of grasses and herbs, however, was the main driver for RS spatial variability in grasslands.
Shu et al. collected soils from degraded grasslands that had undergone 14 years of ecological restoration by planting shrubs with Salix cupularis alone or shrubs with Salix cupularis and mixed grasses, and compared with an extremely degraded grassland as a control. The restoration mode and its interaction with soil depth were crucial for SOC mineralization. Using metagenomics, Zhang et al. analyzed microbial carbohydrate-active enzymes in undisturbed, extensively managed, and intensively managed Moso bamboo plantation. They showed that extensive and intensive management impacts dead plant and microbial biomass decomposition and C turnover, decreased soil C. The established bacterial community was the main driver of C turnover in soils under bamboo plantations.
Linkages between microbial community, C turnover processes, and potential climate changes were examined using freeze-thaw and flood-dry cycles. Yang et al. revealed that freeze–thaw cycles in boreal forest soils activated dissolved organic matter (DOM) and increased its biodegradability, hampering C accumulation and sequestration. These findings highlight the potential of DOM molecular composition to regulate the functional states of soil bacterial communities under increased frequency and intensity of freeze–thaw cycles. Zhu et al. highlighted that the shift from flooding to drying in soils collected from a riparian zone of the Three Gorges Reservoir changes keystone taxa and co-occurrence network properties, which regulated soil respiration of soil aggregates.
Wang et al. studied the responses of prokaryotic, fungal, and cercozoan communities following 5 years of inundation treatments in an experimental wetland. The inundation altered microbial communities in coastal wetlands, and the fungal and cercozoan communities played vital roles in regulating methane emission through microbial interactions with the methane-associated community. Jofré-Fernández et al. investigated the role of soil pH in regulating the production and consumption of reactive oxygen species (ROS) during biotic and abiotic SOM decomposition. The activities of lignin peroxidase, manganese peroxidase, and dye-decolorizing peroxidase were linked with the production of superoxide anion (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). The mechanisms of SOM oxidation by ROS were extremely sensitive to variations in soil pH and the stability of oxidant radicals and the non-radical compounds. Li et al. investigated the occurrence of horizontal gene transfer (HGT) and established the HGT network of C metabolic genes in 764 soil-borne microbiota genomes. The identified inter-microbe HGT genetic traits in soil-borne microbiota genetic sequences, as well as their involvement in the metabolism and regulation processes of organic C suggest a pervasive and substantial effects of HGT on microbial evolution.
Overall, the Research Topic has put in evidence the pivotal role of soil microorganisms in C cycling processes, short- and long-term dynamics of microbial community compositions, CO2 fluxes, and C storage in various ecosystems, including mixed, fir, and deciduous forests, as well as subalpine and alpine meadows, grasses, and intensively managed bamboo plantations. It has expanded our understanding of the complex interplay between soil physico-chemical properties, vegetation, and microbial communities at various spatial and temporal scales. These insights hold promise for the development of effective strategies for C sequestration and advancing our goals of C neutrality and mitigating anthropogenic CO2 emissions.
