Effects of root dominate over aboveground litter on soil microbial biomass in global forest ecosystems

Abstract

Background 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. Methods 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. Results 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. Conclusions 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.

Effects of Litter and Root Manipulations on Soil Bacterial and Fungal Community Structure and Function in a Schrenk’s Spruce (Picea schrenkiana) Forest

“… Crow et al (2009) suggested that changes in the quantity of litter and roots can affect soil microbial diversity by changing soil physicochemical properties. The removal of litter and roots hindered C input belowground, decreased soil microbial biomass C and the diversity of the C source available to the microorganisms, and consequently decreased the soil microbial alpha diversity index ( Jing et al, 2021 ). Additionally, the removal of litter and roots reduce understory plant diversity and carbon source input by changing soil nutrients, thus inhibiting soil microbial diversity ( Zhao et al, 2013 ).…”

“…Soil microbes not only control the decomposition of soil C but also affect the transformation process of soil N (i.e., nitrification and denitrification; Crowther et al, 2015 ; Scarlett et al, 2021 ). It is well known that environmental changes and human activities can alter the quantity of litter and root inputs into the soil in forest ecosystems ( Li et al, 2020 ; Jing et al, 2021 ). These alterations can affect the number and community structure of microorganisms by altering soil nutrient availability and hydrothermal factors ( Liu et al, 2017 ; Santiago et al, 2021 ).…”

“…Previous studies indicated that roots can have a positive or neutral effect on soil microbial diversity ( Wirthner et al, 2011 ), which may be related to the different physiological tolerances of soil microorganisms in response to soil factor changes ( Allison and Martiny, 2008 ). There have been numerous studies of the response of soil microbiota diversity to litter and root manipulations, but an understanding of the mechanisms underlying soil microbial diversity is still limited ( Jing et al, 2021 ). Therefore, more field experiments are needed to better characterize the response of soil microbial diversity to changes in plant detritus and how these changes interact with the regulation of soil nutrients by changing the output and transformation of C and N.…”

Three‐dimensional mapping of carbon, nitrogen, and phosphorus in soil microbial biomass and their stoichiometry at the global scale

“…For example, plants supply rhizosphere‐associated microorganisms with C (Fan et al, 2022; Jackson et al, 2019) and provide nutrients through aboveground and belowground litter input (Meier & Bowman, 2008). As a consequence, vegetation influences the growth, distribution, and stoichiometry of microorganisms in soils, as demonstrated by the close relationships of microbial biomass with plant root biomass and litter input (Jing et al, 2021; Kara et al, 2008). The relative effects of climate, soil physicochemical properties, and vegetation on soil microbial biomass and stoichiometry are difficult to disentangle and are thus rarely reported at the global scale.…”

The role of diversity, body size and climate in dung removal: A correlative and experimental approach

“…For example, plants supply rhizosphere-associated microorganisms with C (Fan et al, 2022;Jackson et al, 2019) and provide nutrients through aboveground and belowground litter input (Meier & Bowman, 2008). As a consequence, vegetation influences the growth, distribution, and stoichiometry of microorganisms in soils, as demonstrated by the close relationships of microbial biomass with plant root biomass and litter input (Jing et al, 2021;Kara et al, 2008). The relative effects of climate, soil physicochemical properties, and vegetation on soil microbial biomass and stoichiometry are difficult to disentangle and are thus rarely reported at the global scale.…”