A recent study has uncovered that not all soil fungi contribute equally to carbon cycling. Researchers found that fungal species occurring across broad geographic regions are the dominant drivers of soil carbon decomposition, while narrowly distributed species contribute far less than previously expected. The study provides new evidence that where microbes occur may be just as important as how many are present when determining ecosystem functioning.
Soils represent one of Earth’s largest carbon reservoirs, storing more carbon than the atmosphere and vegetation combined. The release and storage of this carbon are largely controlled by microorganisms, especially saprotrophic fungi that decompose dead organic matter and recycle nutrients. Yet despite their importance, scientists still know surprisingly little about which fungal groups are responsible for sustaining decomposition across large spatial scales.
To address this question, the research team conducted a large-scale survey covering 847 soil samples collected across 35 provinces in China, spanning approximately 3,400 km from north to south and 3,200 km from east to west. The researchers focused on saprotrophic fungi and classified them according to occupancy—the proportion of sites in which a fungal taxon occurred.
The results revealed a strongly uneven distribution pattern. Nearly 90 percent of fungal taxa were narrowly distributed, occurring in only a small number of locations, whereas only a limited number of fungal taxa showed widespread occurrence across regions. Despite being less diverse locally, widespread saprotrophic fungi exhibited broader environmental tolerance and occupied wider ranges of temperature, precipitation, soil pH, and organic matter conditions. Their diversity also increased toward higher latitudes. In contrast, narrowly distributed fungi showed the opposite pattern and became increasingly dependent on regional species pools and local dispersal processes. Further analyses showed that these contrasting geographic patterns arose from fundamentally different community assembly mechanisms.
Widespread fungi were primarily shaped by environmental filtering, meaning that climate conditions and local soil properties determined where they could persist. Narrow-ranged fungi, however, were more strongly constrained by regional species pools and biotic interactions, indicating that dispersal limitation plays a larger role in determining their distributions. The most important question remained whether these distinct fungal groups contributed differently to ecosystem functioning. To answer this, the researchers linked fungal communities with multiple indicators of carbon decomposition potential, including carbon-degrading genes and enzyme activities. They found that only the diversity of widespread saprotrophic fungi showed strong positive relationships with decomposition-related functions. Because abundant species are often easier to detect, the team further carried out DNA stable isotope probing (DNA-SIP) experiments to directly identify fungal taxa actively decomposing maize straw. The results confirmed that fungi incorporating carbon from decomposing plant residues were predominantly widespread saprotrophic taxa. This finding demonstrates that the stronger associations between widespread fungi and decomposition were not simply statistical artifacts but reflected their genuine functional dominance in carbon turnover.
The study proposes occupancy as a unifying ecological property linking microbial biogeography to ecosystem processes. Rather than local species richness alone, the ability of organisms to persist across diverse environments may determine their contribution to ecosystem functioning at regional and continental scales. The researchers further projected future changes under multiple climate scenarios and found that the diversity of widespread saprotrophic fungi may decline by approximately 25 percent across much of China by 2100. Such reductions could alter decomposition processes and potentially reshape soil carbon storage under future climate change.
By integrating large-scale biogeographic surveys, community assembly analyses, global validation datasets, and experimental verification, the study establishes a new framework for understanding how belowground biodiversity regulates carbon cycling in a changing world. This work combines microbial biogeography, ecological theory, and functional experiments to reveal how differences in geographic distribution shape the ecological roles of soil fungi and ultimately influence terrestrial carbon cycling.
National Science Review
Experimental study