The effects of mixing different leaf litter species on litter decomposition in streams have received considerable attention in recent years. However, contrasting results have been reported and the mechanisms behind the effects of litter diversity have been poorly examined. We compared the decomposition rates and associated fungi for two contrasting litter species, when incubated individually and in mixture, at two different current velocities. Coarse-mesh bags with alder litter individually, oak litter individually and with a mixture of both were incubated in a forest headwater stream over 32 days, under fast or slow current velocities. We determined litter decomposition rates, microbial oxygen consumption rates, and aquatic hyphomycete sporulation rates, species richness and community composition; litter species in the mixture were processed individually. Our results provided weak evidences for diversity effects on leaf litter decomposition. Generally, litter decomposition was unaffected by mixing contrasting litter species, with litter species in the mixture decomposing at the same rate as when incubated individually at both current velocities. The same pattern was observed for microbial variables. Decomposition rates and microbial colonization and activity depended primarily on the traits of the target litter species and were not affected by those of the companion species. However, litter-mixing effects were detected on oak litter at late decomposition stages under fast current velocity conditions, suggesting that both current velocity and the incubation time might influence diversity effects on litter decomposition in streams. This finding contributes to explain the lack of litter-mixing effects reported previously by many studies.

近年来，混合不同落叶物种类对溪流中凋落物分解的影响受到了相当多的关注。然而，已经报道了对比结果，并且对垫料多样性影响背后的机制的研究很少。我们比较了两种对比垃圾物种的分解速率和相关真菌，当单独和混合培养时，在两种不同的电流速度下。分别带有桤木垫料、单独橡木垫料和两者混合的粗网袋在森林源头溪流中以快或慢的流速孵育超过 32 天。我们确定了凋落物分解率、微生物耗氧率和水生丝藻孢子形成率、物种丰富度和群落组成；混合物中的垃圾物种被单独处理。我们的结果为多样性对凋落物分解的影响提供了微弱的证据。通常，垃圾分解不受混合对比垃圾物种的影响，混合物中的垃圾物种以与在两种当前速度下单独孵育时相同的速率分解。对于微生物变量观察到相同的模式。分解率和微生物定植和活动主要取决于目标凋落物物种的性状，不受伴侣物种的影响。然而，在快流速条件下，在分解后期的橡木凋落物上检测到凋落物混合效应，表明流速和孵化时间都可能影响溪流中凋落物分解的多样性效应。