Tree-mycorrhizal types differ in their biomass response to nitrogen addition

A new study reveals that tree symbiotic associations with different mycorrhizal fungi (arbuscular mycorrhizal [AM] vs. ectomycorrhizal [ECM]) are a key predictor of woody biomass carbon (C) gain in response to nitrogen (N) addition. The study was published in Soil Biology and Biochemistry in 2025.

From the South China Botanical Garden of the Chinese Academy of Sciences, the research synthesized data from 125 independent N-addition experiments globally, encompassing 71 tree species and 189 paired observations. For the first time, they quantified the absolute woody biomass C gain per unit N added ( C_perN) for trees associated with AM and ECM fungi. The researchers found that C_perN increased with latitude and was, on average, 6-fold greater in AM trees than in ECM trees (17.2 vs. 2.9 kg C kg N⁻¹). This divergence stems from their distinct N-acquisition strategies: ECM fungi can directly access organic N, making their host trees less responsive to additional N inputs, whereas AM trees rely more on inorganic N and thus benefit more from N deposition.

Using a global map of tree-mycorrhizal distributions, the team estimated that ignoring these mycorrhizal-type effects leads to a significant overestimation of N-induced tree C sequestration by 12% (9.8 Tg C yr⁻¹) globally and 17% (9.4 Tg C yr⁻¹) in temperate forests. This overestimation occurs primarily because ECM trees, which have a low C_perN, dominate many temperate forests, particularly in Europe.

The findings suggest that the future forest C sink under continued N deposition may be strongly influenced by shifts in the relative abundance of AM and ECM trees. Tree species with more acquisitive nutrient use strategies (such as AM trees) may be positioned to sequester more C than those with conservative strategies (ECM trees). Therefore, integrating mycorrhizal type as a key biological mechanism into global biogeochemical models is critical for improving projections of the forest carbon cycle and its feedback to climate change. Paper link: https://authors.elsevier.com/c/1lkOK8g13fGzt

Figure. A. Model-averaged importance of the predictors of nitrogen addition impacts on tree biomass C_perN. B. Changes of woody biomass C_perN in tree species that associated with arbuscular mycorrhizal fungi (AM trees) and ectomycorrhizal fungi (ECM trees) with latitude and across biomes. C. Global distribution of nitrogen-induced tree carbon sequestration. (Image by CHEN et al)