A new study led by Dr. Guanghui Yu from School of Earth System Science, Tianjin University, delves into the role of fungal biomass on the formation of soil stable carbon.
Fungi play a crucial role in ecosystem processes such as soil carbon cycling, decomposition, nutrient turnover, and symbiosis with plants. Most vascular plants form mycorrhizae, where fungi exchange carbon for nutrients like phosphorus and nitrogen.
Fungal hyphae can extend over vast areas, influencing the “hyphosphere”, a zone larger and more dynamic than the rhizosphere. When fungi die, their hyphal fragments contribute to microbial residues, or “necromass”, which are key to forming mineral-associated organic matter (MAOM).
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Fungal necromass is significant in soil organic matter, especially in topsoil, and is sensitive to climate change and management. Despite the importance of fungi in carbon cycles, their role in stabilizing carbon over long timescales is not fully understood.
Carbon persistence
This study, conducted by Xiang Wang and Guanghui Yu, explores the role of fungal biomass in carbon persistence across biomes. The researchers hypothesize that hypha-mineral interactions help stabilize carbon. They analyzed fungal biomass and mineral-associated carbon in six biomes and used nanoscale imaging to study hypha-mineral interactions in Pinus silvestris rhizospheres. Findings show fungi’s vital role in stabilizing carbon in soils, with implications for global carbon cycling.
The researchers collected data on microbial biomass carbon stocks and reactive mineral-associated carbon stocks from six different ecosystems to better understand the critical role of microbial biomass in forming stable soil carbon pools at the ecosystem level.
The results revealed a strong correlation between microbial biomass carbon and reactive mineral-associated carbon, indicating their significant contribution to the persistence and stability of soil carbon. The topsoil microbial biomass carbon accounted for 86% of the total microbial biomass carbon, showing a clear connection to the entire soil profile’s microbial carbon stock. Interestingly, fungal biomass carbon in the topsoil was strongly correlated with the reactive mineral-associated carbon across the whole soil profile, while bacterial biomass carbon showed a weaker correlation.
Mineral coating layer
To investigate the hypha-mineral interactions and uncover the key mechanisms behind the persistence of fungal biomass carbon, the researchers used high-resolution nanoscale secondary ion mass spectrometry (50 nm resolution) to analyze mycorrhizae in the pine rhizosphere soil. The results revealed that hyphae were surrounded by a distinct mineral coating layer, approximately 500–600 nm thick. This mineral coating, closely associated with carbon, provided direct evidence that mineral nanoparticles help protect fungal exudates.
The study proposes a new conceptual model to explain these interactions, emphasizing the multifaceted roles fungi play in soil organic carbon persistence. According to the model, living fungi contribute to the soil biogeochemical carbon cycle in two ways: First, hypha-mineral interactions generate reactive oxygen species that accelerate organic matter decomposition, enhancing nutrient cycling. Second, the nanoparticles produced by fungi facilitate the formation of organo-mineral complexes, which stabilize soil organic carbon. After death, fungal necromass interacts with nanoparticles, further stabilizing the carbon.
The findings of this study bring together ecosystem-level processes and microscopic mechanisms, offering new insights into the important role fungi play in stabilizing soil carbon and contributing to long-term carbon storage.
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