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1. Soil CO 2 and O 2 Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

   https://doi.org/10.2136/sssaj2019.02.0049  

   Hodges, Caitlin ; Kim, Hyojin ; Brantley, Susan L. ; Kaye, Jason ( July 2019 , Soil Science Society of America Journal)
2. Soil carbon dioxide emissions from the Mojave desert: Isotopic evidence for a carbonate source: Abiotic Soil CO 2 Emissions

   https://doi.org/10.1002/2016GL071198  

   Soper, Fiona M. ; McCalley, Carmody K. ; Sparks, Kimberlee ; Sparks, Jed P. ( January 2017 , Geophysical Research Letters)
3. Wetting‐induced soil CO2 emission pulses are driven by interactions among soil temperature, carbon, and nitrogen limitation in the Colorado Desert

   https://doi.org/10.1111/gcb.16669  

   Andrews, Holly M. ; Krichels, Alexander H. ; Homyak, Peter M. ; Piper, Stephanie ; Aronson, Emma L. ; Botthoff, Jon ; Greene, Aral C. ; Jenerette, G. Darrel ( March 2023 , Global Change Biology)

   Warming‐induced changes in precipitation regimes, coupled with anthropogenically enhanced nitrogen (N) deposition, are likely to increase the prevalence, duration, and magnitude of soil respiration pulses following wetting via interactions among temperature and carbon (C) and N availability. Quantifying the importance of these interactive controls on soil respiration is a key challenge as pulses can be large terrestrial sources of atmospheric carbon dioxide (CO₂) over comparatively short timescales. Using an automated sensor system, we measured soil CO₂flux dynamics in the Colorado Desert—a system characterized by pronounced transitions from dry‐to‐wet soil conditions—through a multi‐year series of experimental wetting campaigns. Experimental manipulations included combinations of C and N additions across a range of ambient temperatures and across five sites varying in atmospheric N deposition. We found soil CO₂pulses following wetting were highly predictable from peak instantaneous CO₂flux measurements. CO₂pulses consistently increased with temperature, and temperature at time of wetting positively correlated to CO₂pulse magnitude. Experimentally adding N along the N deposition gradient generated contrasting pulse responses: adding N increased CO₂pulses in low N deposition sites, whereas adding N decreased CO₂pulses in high N deposition sites. At a low N deposition site, simultaneous additions of C and N during wetting led to the highest observed soil CO₂fluxes reported globally at 299.5 μmol CO₂ m⁻² s⁻¹. Our results suggest that soils have the capacity to emit high amounts of CO₂within small timeframes following infrequent wetting, and pulse sizes reflect a non‐linear combination of soil resource and temperature interactions. Importantly, the largest soil CO₂emissions occurred when multiple resources were amended simultaneously in historically resource‐limited desert soils, pointing to regions experiencing simultaneous effects of desertification and urbanization as key locations in future global C balance.

    

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4. Improving the accuracy of the gradient method for determining soil carbon dioxide efflux: Accurate Long-Term F soil Based on the GM

   https://doi.org/10.1002/2016JG003530  

   Sánchez-Cañete, Enrique P. ; Scott, Russell L. ; van Haren, Joost ; Barron-Gafford, Greg A. ( January 2017 , Journal of Geophysical Research: Biogeosciences)
5. Multiple constraints cause positive and negative feedbacks limiting grassland soil CO 2 efflux under CO 2 enrichment

   https://doi.org/10.1073/pnas.2008284117  

   Fay, Philip A. ; Hui, Dafeng ; Jackson, Robert B. ; Collins, Harold P. ; Reichmann, Lara G. ; Aspinwall, Michael J. ; Jin, Virginia L. ; Khasanova, Albina R. ; Heckman, Robert W. ; Polley, H. Wayne ( January 2021 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   Terrestrial ecosystems are increasingly enriched with resources such as atmospheric CO 2 that limit ecosystem processes. The consequences for ecosystem carbon cycling depend on the feedbacks from other limiting resources and plant community change, which remain poorly understood for soil CO 2 efflux, J CO2 , a primary carbon flux from the biosphere to the atmosphere. We applied a unique CO 2 enrichment gradient (250 to 500 µL L −1 ) for eight years to grassland plant communities on soils from different landscape positions. We identified the trajectory of J CO2 responses and feedbacks from other resources, plant diversity [effective species richness, exp(H)], and community change (plant species turnover). We found linear increases in J CO2 on an alluvial sandy loam and a lowland clay soil, and an asymptotic increase on an upland silty clay soil. Structural equation modeling identified CO 2 as the dominant limitation on J CO2 on the clay soil. In contrast with theory predicting limitation from a single limiting factor, the linear J CO2 response on the sandy loam was reinforced by positive feedbacks from aboveground net primary productivity and exp(H), while the asymptotic J CO2 response on the silty clay arose from a net negative feedback among exp(H), species turnover, and soil water potential. These findings support a multiple resource limitation view of the effects of global change drivers on grassland ecosystem carbon cycling and highlight a crucial role for positive or negative feedbacks between limiting resources and plant community structure. Incorporating these feedbacks will improve models of terrestrial carbon sequestration and ecosystem services. 

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