Background and aims
Fine-root (diameter ≤ 2 mm) decomposition contributes significantly to nutrient cycling in terrestrial ecosystems. Roots with arbuscular mycorrhizas (AM) and ectomycorrhizas (ECM) differ in root chemistry, which might affect root decomposition rate, but whether this effect differs across forest biomes is unknown.

Methods
We used a compiled dataset from temperate and (sub)tropical forests (168 species from 84 studies) to investigate how root chemistry and climate influence fine-root decomposition with different mycorrhizal associations in (sub)tropical and temperate forests.

Results
We show that AM trees exhibited faster fine-root decomposition rates than ECM trees did in temperate forests, but not in (sub)tropical forests. In temperate forests, root decomposition rates decreased with increasing root lignin concentrations, and ECM trees had higher root lignin concentrations than AM trees did which likely caused the difference in their decomposition rates. In (sub)tropical forests, root decomposition rates were mainly determined by root phosphorus (P) concentration. ECM and AM trees had similar root P concentrations, and thus their root decomposition rates were similar. In addition, the root decomposition rate was not affected by climate in (sub)tropical or temperate forests. However, the root decomposition rates of both AM and ECM trees were similarly affected by root chemistry and climate for all forests.

Conclusions
The findings will help us better predict tree species effects on ecosystem processes by considering their mycorrhizal association, particularly in temperate forests, where AM and ECM species co-occur. Additionally, the findings provide a framework for linking the dynamics of organic matter in forests to fine root quality and climate.