Forest ecosystems play a vital role in the global carbon cycle. While the significance of tree mycorrhizal fungi in this process is well-documented, the manner in which different types of tree mycorrhizae influence forest carbon storage, particularly in species-rich subtropical forests, remains poorly understood.

To fill this knowledge gap, a research team from the Wuhan Botanical Garden (WBG) of the Chinese Academy of Sciences, carried out a systematic study in the subtropical mountain forest of Badagongshan. Their findings were recently published in Forest Ecology and Management.

Along a gradient of ectomycorrhizal (ECM) tree dominance, the researchers established 58 sampling plots to assess the impact of ECM dominance on forest carbon stocks. These stocks include three key components: tree biomass carbon, forest floor carbon, and soil carbon.

The study revealed a clear positive trend: total forest carbon stocks increased as ECM tree dominance rose. Specifically, both tree biomass carbon and forest floor carbon showed a positive correlation with ECM dominance. In contrast, soil carbon storage exhibited no meaningful association with ECM tree dominance.

Further analysis identified the drivers behind these patterns. The increase in tree biomass carbon was primarily linked to the higher density of large-size trees in stands dominated by ECM species. Meanwhile, the accumulation of forest floor carbon was mainly attributed to the lower litter quality of ECM trees -- characterized by a higher carbon-to-nitrogen (C:N) ratio, which slows down decomposition.

A notable finding from the research is that despite ECM-dominated plots containing larger vegetation and litter carbon pools, this advantage did not translate into greater soil carbon storage. The team suggests this discrepancy may be related to two factors: the peroxidase activity of ECM fungi and the relatively low microbial carbon use efficiency in ECM-dominated stands.

These results highlight the critical role of tree mycorrhizal types in shaping forest carbon storage, especially in subtropical regions.

Location of the 58 plots along a gradient of ECM tree dominance in the subtropical mountainous forest. (Image by WBG)

The effect of ECM tree dominance on different components of forest carbon stock. (Image by WBG)