Microbial proxies for anoxic microsites vary with management and partially explain soil carbon concentration

Authors: LACROIX, EMILY - Stanford University; GOMES, ANNA - Stanford University; BARRATT-HEITMANN, GABRIELLA - Stanford University; SCHULER, DYLAN - Stanford University; DEKAS, ANNE - Stanford University; LIPTZIN, DANIEL - Soil Health Institute; ABERLE, EZRA - North Dakota State University; Watts, Dexter; NELSON, KELLY - University Of Missouri; CULMAN, STEVEN - Washington State University; FENDORF, SCOTT - Stanford University

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2024
Publication Date: 6/14/2024
Citation: Lacroix, E.M., Gomes, A., Barratt-Heitmann, G., Schuler, D., Dekas, A., Liptzin, D., Aberle, E., Watts, D.B., Nelson, K., Culman, S., Fendorf, S. 2024. Microbial proxies for anoxic microsites vary with management and partially explain soil carbon concentration. Environmental Science and Technology. 58(26):11459-11469. https://doi.org/10.1021/acs.est.4c01882.
DOI: https://doi.org/10.1021/acs.est.4c01882

Interpretive Summary: Influence of how microbial activity occurring in anaerobic pockets of soil can contribute to the formation of soil organic C has had limited study. The microbial activity within in these anerobic pockets may also be influence by climate, soil properties, and agricultural management. Thus, a study was conducted using droplet digital PCR to quantified anaerobe DNA in soils from four long-term agricultural experiments in the Upper Midwest to the Southeast of the United States. Anaerobe abundance was used as a proxy for anaerobic microsites to examine how anaerobic microsites (microbial activity in anaerobic soil pockets) varied with soil properties and agricultural management, specifically, organic matter amendments, tillage practices, and agricultural use (i.e., comparison to an uncultivated control). Anaerobe abundance was associated with soil properties corresponding to oxygen supply, such as clay content, and oxygen demand. Anaerobic microsites also responded to management; in particular, practices that altered oxygen demand (e.g., organic matter amendments, cultivation status) had a greater effect on anaerobe abundance than practices that regulated oxygen supply (e.g., tillage). Finally, anaerobe abundance was positively correlated with soil C content. Compared to other mutable soil C protection mechanisms, anaerobe abundance explained the greatest unique variance in soil C content across cropland soils. Together, our results suggest that anaerobic microsites are ubiquitous, responsive to management, and can be leveraged to increase soil C storage within agricultural soils.

Technical Abstract: Anaerobic microsites, volumes of anaerobic activity within seemingly aerobic soils, are under-explored contributors to soil organic carbon (C) stabilization. How anaerobic microsites vary with climate, soil properties, and management and the degree to which anaerobic microsites contribute to soil C stabilization remain unknown. Using droplet digital PCR, we quantified anaerobe DNA in soils from four long-term agricultural experiments in the Upper Midwest to the Southeast of the United States. We used anaerobe abundance as a proxy for anaerobic microsites and examined how anaerobic microsites varied with soil properties and management, specifically, organic matter amendments, tillage practices, and agricultural use (i.e., comparison to an uncultivated control). Anaerobe abundance was associated with soil properties corresponding to oxygen supply, such as clay content, and oxygen demand, such as 16S rRNA abundance. Anaerobic microsites also responded to management; in particular, practices that altered oxygen demand (e.g., organic matter amendments, cultivation status) had a greater effect on anaerobe abundance than practices that regulated oxygen supply (e.g., tillage). Finally, anaerobe abundance was positively correlated with soil C content. Compared to other mutable soil C protection mechanisms, anaerobe abundance explained the greatest unique variance in soil C content across cropland soils. Together, our results suggest that anaerobic microsites are ubiquitous, responsive to management, and can be leveraged to increase soil C storage within agricultural soils.