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Climatic controls on soil carbon accumulation and loss in a dryland ecosystems

November 17, 2021

Arid and semiarid ecosystems drive year-to-year variability in the strength of the terrestrial carbon (C) sink, yet there is uncertainty about how soil C gains and losses contribute to this variation. To address this knowledge gap, we embedded C-depleted soil mesocosms, containing litter or biocrust C inputs, within an in situ dryland ecosystem warming experiment. Over the course of one year, changes in microbial biomass and total soil organic C pools were monitored alongside hourly measurements of soil CO2 flux. We also developed a biogeochemical model to explore the mechanisms that gave rise to observed soil C dynamics. Field data and model simulations demonstrated that water exerted much stronger control on soil biogeochemistry than temperature, with precipitation events triggering large CO2 pulses and transport of litter- and biocrust-derived C into the soil profile. We expected leaching of organic matter would result in steady accumulation of C within the mineral soil over time. Instead, the size of the total organic C pool fluctuated throughout the year, largely in response to microbial growth: increases in the size of microbial biomass were negatively correlated with the quantity of C residing in the top 2 cm, where most biogeochemical changes were observed. Our data and models suggest that microbial responses to precipitation events trigger rapid metabolism of dissolved organic C inputs, which strongly limit accumulation of autotroph-derived C belowground. Accordingly, changes in the magnitude and/or frequency of precipitation events in this dryland ecosystem could have profound impacts on the strength of the soil C sink.

Citation Information

Publication Year 2021
Title Climatic controls on soil carbon accumulation and loss in a dryland ecosystems
DOI 10.1029/2021JG006492
Authors Bonnie G. Waring, Kenneth R Smith, Edmund E. Grote, Armin J. Howell, Robin H. Reibold, Colin L Tucker, Sasha Reed
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research
Series Number
Index ID 70227171
Record Source USGS Publications Warehouse
USGS Organization Southwest Biological Science Center