Inputs of above- and belowground litter into forest soils are changing at an unprecedented rate due to continuing human disturbances and climate change. Microorganisms drive the soil carbon (C) cycle, but the roles of above- and belowground litter in regulating the soil microbial community have not been evaluated at a global scale. Here, we conducted a meta-analysis based on 68 aboveground litter removal and root exclusion studies across forest ecosystems to quantify the roles of above- and belowground litter on soil microbial community and compare their relative importance. Aboveground litter removal significantly declined soil microbial biomass by 4.9% but root exclusion inhibited it stronger, up to 11.7%. Moreover, the aboveground litter removal significantly raised fungi by 10.1% without altering bacteria, leading to a 46.7% increase in the fungi-to-bacteria (F/B) ratio. Differently, root exclusion significantly decreased the fungi by 26.2% but increased the bacteria by 5.7%, causing a 13.3% decrease in the F/B ratio. Specifically, root exclusion significantly inhibited arbuscular mycorrhizal fungi, ectomycorrhizal fungi, and actinomycetes by 22.9%, 43.8%, and 7.9%, respectively. The negative effects of aboveground litter removal on microbial biomass increased with mean annual temperature and precipitation, whereas that of root exclusion on microbial biomass did not change with climatic factors but amplified with treatment duration. More importantly, greater effects of root exclusion on microbial biomass than aboveground litter removal were consistent across diverse forest biomes (expect boreal forests) and durations. These data provide a global evidence that root litter inputs exert a larger control on microbial biomass than aboveground litter inputs in forest ecosystems. Our study also highlights that changes in above- and belowground litter inputs could alter soil C stability differently by shifting the microbial community structure in the opposite direction. These findings are useful for predicting microbe-mediated C processes in response to changes in forest management or climate.

中文翻译：

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根占地上凋落物对全球森林生态系统土壤微生物生物量的影响

由于持续的人类干扰和气候变化，地上和地下垃圾对森林土壤的输入正在以前所未有的速度发生变化。微生物驱动土壤碳 (C) 循环，但尚未在全球范围内评估地上和地下凋落物在调节土壤微生物群落中的作用。在这里，我们基于整个森林生态系统的 68 项地上垃圾清除和根排除研究进行了荟萃分析，以量化地上和地下垃圾对土壤微生物群落的作用并比较它们的相对重要性。地上凋落物清除显着降低了土壤微生物生物量 4.9%，但根排斥对其抑制作用更强，高达 11.7%。此外，在不改变细菌的情况下，清除地上垃圾显着增加了 10.1% 的真菌，导致 46. 真菌与细菌 (F/B) 的比率增加了 7%。不同的是，根排除显着减少了 26.2% 的真菌，但增加了 5.7% 的细菌，导致 F/B 比降低 13.3%。具体而言，根排斥分别显着抑制丛枝菌根真菌、外生菌根真菌和放线菌 22.9%、43.8% 和 7.9%。清除地上凋落物对微生物生物量的负面影响随着年平均温度和降水量的增加而增加，而根系排除对微生物生物量的负面影响不随气候因素而变化，但随着处理时间的延长而放大。更重要的是，根系排除对微生物生物量的影响大于地上凋落物清除的影响在不同的森林生物群落（预计北方森林）和持续时间中是一致的。这些数据提供了一个全球证据，表明在森林生态系统中，根凋落物输入对微生物生物量的控制比地上凋落物输入更大。我们的研究还强调，地上和地下凋落物输入的变化可以通过向相反方向移动微生物群落结构来不同地改变土壤碳稳定性。这些发现有助于预测响应森林管理或气候变化的微生物介导的碳过程。