EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils

Noah Sokol1, Steve Blazewicz1, Megan Foley2, Alex Greenlon3, and Jennifer Pett-Ridge1
Noah Sokol et al.
  • 1Lawrence Livermore National Laboratory, Physical & Life Sciences Directorate, United States of America (
  • 2Northern Arizona University, Center for Ecosystem Studies, United States of America
  • 3University of California Berkeley, Department of Environmental Policy, Science, and Management, United States of America

Carbon use efficiency (CUE) is theorized to be positively associated with the formation of microbially-derived, mineral-associated soil carbon.  Yet few empirical studies have directly tested this relationship. Moreover, it is unclear: (1) how differences between distinct soil microbial communities (for example, differences in competitive interactions and/or growth rate among rhizosphere, detritusphere, and bulk soil communities) may yield different relationships between carbon-use efficiency and soil carbon formation, and (2) how microbial ecophysiology – such as physiological changes induced by drought – may modulate the strength and/or direction of the CUE-soil carbon relationship.

To investigate these questions, we conducted a 12-week 13C tracer study to track the movement of two dominant sources of plant carbon – rhizodeposition and root detritus – into soil microbial communities and carbon pools under normal moisture vs drought conditions. Using a continuous 13CO2-labeling system, we grew the Mediterranean annual grass Avena barbata in controlled growth chambers and measured the formation of organic matter from 13C-enriched rhizodeposition. As the plants grew, we harvested rhizosphere and bulk soil at three time points (4, 8, and 12 weeks) to capture changes in soil carbon pools and microbial community dynamics. In parallel microcosms, we tracked the formation of soil carbon derived from 13C-enriched A. barbata root detritus during 12 weeks of decomposition; harvesting detritusphere and bulk soil at 4,8, and 12 weeks. In all microcosms, we manipulated soil moisture to generate drought (7.8 ± 2.1 % soil moisture) and ‘normal moisture’ (15.1 ± 4.2 % soil moisture) treatments.

In all samples (over 150 observations), we measured CUE via the 18O-H2O method, and quantified the formation of different 13C-soil organic carbon pools via density fractionation. Here we will present data on how soil moisture influences CUE in rhizosphere, detritusphere, and bulk soil communities, and whether differences in CUE are correlated with the formation of mineral-associated soil organic carbon. These results will help to illustrate whether CUE acts as a lynchpin variable with predictive power for stable soil carbon formation, or whether other microbial traits may require consideration.



How to cite: Sokol, N., Blazewicz, S., Foley, M., Greenlon, A., and Pett-Ridge, J.: How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13148,, 2020.

This abstract will not be presented.