The Global Distribution Of Fine Root Traits And Respiratory Carbon Emissions

Fine roots play a crucial role in maintaining the productivity of terrestrial ecosystems by absorbing nutrients and participating in biogeochemical cycles through processes such as respiration and turnover.Root traits are often predictive of root function,and previous studies have studied the fine root morphology and chemical traits of numerous plant species worldwide.However,global vegetation often responds to environmental changes at the plant community level,but how community-level root morphology and chemical traits vary along the environmental gradients remains poorly understood.Furthermore,the impacts of fine-root processes on the biogeochemical cycles depend on not only the root morphology and chemical traits,but also the length and biomass of the fine roots.Therefore,this study aims to investigate the global distribution pattern of community-level root morphology,chemistry,length,biomass and key functions of the plant fine roots.（1）This study assigned the fine root trait data such as root diameter,specific root length（root length per unit dry weight）,root tissue density,and root nitrogen concentration to plant species from more than 80,000 vegetation plots worldwide.The random forest model was employed to analyze the relationships between community-level fine root morphology and chemical traits and the corresponding environmental factors,and to simulate the spatial distribution patterns of fine root morphology and chemical traits at the global scale.The results indicate that tropical communties exhibits a larger fine root diameter,shorter specific root length and higher tissue density than temperate communties.Compared to grassland communities,forest and shrubland communities have larger root diameters,smaller root lengths,and higher tissue density.Climate factors are key drivers of the spatial variaitons in root diameter and specific root length,whereas soil texture factors are key drivers of the spatial variaitons in tissue density and nitrogen concentraiton.（2）This study collected global data of fine root length density form 549 sampling sites in 376 publications.Using the random forest model,the global spatial distribution patterns of fine root length density were simulated.Fine root biomass and surface area were estimated by linking root length density with root diameter and specific root length.The results revealed that fine root length density in temperate biomes was significantly higher than in tropical biomes.The spatial variations in global fine root length density were mainly influenced by the maximum temperature of the warmest month,the content of coarse fragments volumetric,soil water content,and soil organic matter content.The estimated total fine root length of global vegetationwas approximately7.7×10¹⁴ km,with a surface area of 9.3×10⁸ km²,and a fine root biomass of 7.5 Pg.（3）This study investigated the global distribution patterns of fine root respiration rate and respiratory fluxes.Fine root respiration,as a crucial physiological and ecological process,is an important component of ecosystem carbon cycling.The study constructed a global database of fine root respiration rates by measuring the in situ fine-root respiration across 252 species,and collecting respiration rate data across 245species from the literature.An empirical model for predicting fine root respiration rates was developed by analyzing the relationship between fine root respiration rates and other fine root traits.In conjunction with fine root biomass data,the global distribution pattern of fine root respiratory fluxes and total carbon emissions of fine root respiration were estimated.This study found significant correlations between fine root respiration rate and specific root length across different growth types（woody vs.herbaceous）,mycorrhizal types（ectomycorrhizal vs.arbuscular mycorrhizal）,and climates（temperate vs.subtropical）.Globally,fine root respiration rates and respiratory fluxes at local temperature were significantly higher in tropical regions compared to temperate regions.The annual carbon emissions from global fine root respiration were approximately 12.0 Pg.This study analyzed the spatial distribution of fine morphology,chemistry,length,biomass and respiration at the global scale.Results of this study can help us to better explore the diverse fine-root adaptive strategies across the Earth’s terrestrial surface,as well as the global impacts of fine-root functions on belowground ecological processes.This study also provided the important root data for the simulation studies of nutrient and carbon cycles in terrestrial ecosystems.