Abstract
BackgroundInputs 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.MethodsHere, 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.ResultsAboveground 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.ConclusionsThese 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.
Highlights
Intensified human disturbances and climate change have greatly influenced above- and belowground litter inputs to forest soils
Above- and belowground litters differ in chemical properties, turnover rates, and pathways entering into the soil (Hatton et al 2015; Fulton-Smith and Cotrufo 2019; Sokol et al 2019), meaning that they may exert different controls on soil microorganisms
In comparison to the above-ground litter removal, root exclusion caused a stronger decline in the microbial biomass, reaching11.7% (Fig. 2b, P < 0.05)
Summary
Intensified human disturbances and climate change have greatly influenced above- and belowground litter (root) inputs to forest soils. Harvesting forest products significantly decreases the aboveground litter input (Achat et al 2015), but nutrient deposition may increase litter inputs more from aboveground than belowground parts via enhanced plant growth and decreased root-toshoot ratios (Song et al 2019; Li et al 2020) These changes in litter inputs can profoundly alter soil carbon (C) stocks, because plant litters are the main source of C into the soil (Lajtha et al 2018; Reynolds et al 2018). Numerous studies have quantified the roles of above- and belowground litter in driving the soil microbial community via litter removal experiments (Hogberg et al 2007; Weintraub et al 2013; Xu et al 2013; Wang et al 2017a; vanden Enden et al, 2018; Jing et al 2019). 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
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