1. Litter decomposition is a fundamental process for nutrient cycling and C fluxes between terrestrial ecosystems and the atmosphere. Multiple factors such as environmental conditions, litter quality and decomposer organisms are known to influence this ecological process in direct and indirect ways. However, it remains poorly understood to what extent this entangled bank of complex interactions can be disrupted by several global change drivers such as climate change and invasive species.
2. Here we reported main findings from a litter decomposition experiment conducted in a natural mixed forest invaded by Phytophthora cinnamomi, an exotic oomycete well known for causing tree disease and forest decline. In two Mediterranean forest types (namely woodland and closed forest), we first built a rainfall exclusion infrastructure to reduce natural precipitation by 30%. Then, we followed the spatial variation in C and N leaf litter dynamics as well as the abundance of the exotic oomycete P. cinnamomi for 18 months under both control and rainfall exclusion conditions using a litter bag methodology with different mesh sizes to further evaluate the indirect role of mesofauna abundance and diversity in litter C and N temporal dynamics.
3. Significant reductions in soil moisture produced by the experimental rainfall exclusion increased C litter loss with time directly, and indirectly via increases in overall mesofauna abundance and changes in the ratio between predators and decomposers. N litter dynamics were in contrast modulated mainly by initial litter quality. Surprisingly, P. cinnamomi abundance did not correlate with variation in initial litter quality as previously suggested, but we found that the exotic oomycete was negatively correlated with both decomposer and predator abundances. These results suggest it might participate indirectly in litter decomposition dynamics through the biotic soil component.
4. Synthesis. Contrary to expected, our results show that a moderate but realistic rainfall reduction can accelerate the litter decomposition process. It also points out to litter fauna as a key component modulating the indirect impacts of global change drivers on litter decomposition.

中文翻译：

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土壤动物群调节实验性干旱对外来病原体入侵森林中凋落物分解的影响

1. 凋落物分解是陆地生态系统和大气之间养分循环和碳通量的基本过程。众所周知，环境条件、凋落物质量和分解生物等多种因素会以直接和间接方式影响这一生态过程。然而，人们仍然知之甚少，这种错综复杂的相互作用会在多大程度上被气候变化和入侵物种等全球变化驱动因素破坏。
2. 在这里，我们报告了在Phytophthora cinnamomi入侵的天然混交林中进行的凋落物分解实验的主要发现，Phytophthora cinnamomi 是一种以引起树木疾病和森林衰退而闻名的外来卵菌。在两种地中海森林类型（即林地和封闭森林）中，我们首先建立了降雨排除基础设施，将自然降水减少了 30%。然后，我们跟踪了 C 和 N 叶凋落物动态的空间变化以及外来卵菌P的丰度。cinnamomi在控制和降雨排除条件下使用具有不同网格尺寸的垃圾袋方法进一步评估中型动物群丰度和多样性在垃圾 C 和 N 时间动态中的间接作用。
3. 实验性降雨排除所产生的土壤水分显着减少随着时间的推移直接增加了 C 凋落物的损失，并通过整体中型动物群丰度的增加和捕食者和分解者之间比率的变化间接增加了。相比之下，N 窝动态主要受初始窝质量的影响。令人惊讶的是，P. cinnamomi丰度与之前建议的初始凋落物质量的变化无关，但我们发现外来卵菌与分解者和捕食者的丰度都呈负相关。这些结果表明它可能通过生物土壤成分间接参与凋落物分解动力学。
4. 合成。与预期相反，我们的结果表明适度但现实的降雨减少可以加速凋落物分解过程。它还指出，垃圾动物群是调节全球变化驱动因素对垃圾分解的间接影响的关键组成部分。