Slower leaf litter decomposition rates for trees associated with ectomycorrhizal (ECM) fungi compared to arbuscular mycorrhizal (AM) fungi may lead to the development of conservative nitrogen cycling and accumulation of soil organic matter in surface soils of ECM-dominated forests. Slower decomposition is hypothesized to occur via two often-confounded mechanisms: production of lower quality litter by ECM-associated trees compared to AM-associated trees and competition for nitrogen between ECM and saprotrophic decomposers in ECM-dominated stands. To disentangle the effects of litter quality and stand mycorrhizal type on decomposition, we measured litter mass loss rates of two AM species higher and two AM species similar in chemical quality to two ECM species. Leaf litter was decomposed for two years in neighboring ECM- and AM-dominated stands of a wet tropical montane forest. Litter phosphorus (P) was the strongest predictor of decomposition rates across all species, with no effect of litter mycorrhizal type on decomposition rates. Only one species, which exhibited intermediate litter chemical quality and decomposition rate, decomposed significantly faster in AM- compared to ECM-dominated stands. Leaf litter decomposition rates cannot be predicted directly from litter mycorrhizal type or stand mycorrhizal type because litter chemical quality and environmental conditions mediate the manifestation of slower decomposition in ECM stands.

与丛枝菌根（AM）真菌相比，与外生菌根（ECM）真菌相关的树木的凋落物分解速率较慢，这可能导致保守的氮循环的发展以及ECM为主的森林表层土壤中有机质的积累。据推测，分解速度较慢是通过两种常被混淆的机制发生的：与AM关联树相比，ECM关联树生产的凋落物质量较低，在ECM主导的林分中，ECM与腐化分解物之间的氮竞争。为了弄清楚垫料质量和菌根类型对分解的影响，我们测量了两个AM种类和两个AM种类的化学质量与两个ECM种类相似的垫料质量损失率。在潮湿的热带山地森林附近的以ECM和AM为主的林分中，枯枝落叶被分解了两年。凋落物磷（P）是所有物种中分解速率的最强预测指标，而凋落菌根类型对分解速率没有影响。与ECM为主的林分相比，只有一种具有中等凋落物化学质量和分解速率的树种在AM处的分解速度显着加快。由于凋落物的化学质量和环境条件介导了ECM林分中较慢分解的表现，因此不能直接根据凋落物的菌根类型或林分菌根类型来预测叶片凋落物的分解速率。凋落菌根类型对分解速率没有影响。与ECM为主的林分相比，只有一种具有中等凋落物化学质量和分解速率的树种在AM处的分解速度显着加快。由于凋落物的化学质量和环境条件介导了ECM林分中较慢分解的表现，因此不能直接根据凋落物的菌根类型或林分菌根类型来预测叶片凋落物的分解速率。凋落菌根类型对分解速率没有影响。与ECM为主的林分相比，只有一种具有中等凋落物化学质量和分解速率的树种在AM中的分解速度显着加快。由于凋落物的化学质量和环境条件介导了ECM林分中较慢分解的表现，因此不能直接根据凋落物的菌根类型或林分菌根类型来预测叶片凋落物的分解速率。