Decomposition of urban atmospheric carbon in Sonoran Desert soils
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Urban atmospheres can have high concentrations of particulate organic carbon (oC) but the rate and fate oC deposition in near-urban ecosystems are rarely quantified. We collected atmospheric particulate matter in Phoenix, AZ and applied these samples to Sonoran Desert soils in a series of laboratory incubation experiments. The addition of fine particulate matter (<2.5 μm aerodynamic diameter) increased microbial respiration in soils collected from the interspaces between desert shrubs. The increase in soil respiration was equivalent to 25% to 30% of the added oC. In contrast, we did not detect increases in respiration when coarse particulate matter (>2.5 μm aerodynamic diameter) was added to interspace soils, suggesting that coarse particulate oC is recalcitrant to microbial decomposition. Due to comparatively higher background levels of C mineralization, we rarely detected changes in microbial respiration when fine or coarse particulate oC was added to soils collected beneath shrub canopies. We measured total atmospheric C concentrations within and surrounding Phoenix and, using inferential methods, estimated rates of deposition that ranged from 0.02 to 0.58 mg C m−2 d−1 for fine particles and from 0 to 6.15 mg C m−2 d−1 for coarse particles. Results show that fine atmospheric particulate matter deposited at low rates downwind of Phoenix is a labile oC substrate for soil heterotrophs. In contrast, oC deposited at higher rates as coarse particulate matter may accumulate in soils due to slow microbial decomposition rates.
KeywordsCarbon deposition Particulate matter Sonoran Desert Soil respiration Urban
This material is based upon work supported by the National Science Foundation under Grant No. DEB-0423704 [Central Arizona - Phoenix Long-Term Ecological Research (CAP LTER)] and the NSF Ecosystem Studies Program (DEB-0514382 and DEB-0514379). Any opinions, findings and conclusions or recommendation expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF). We thank two anonymous reviewers for valuable comments on our manuscript; David Huber, Quincy Stewart, and Sam Norlin for field and laboratory support; and Pierre Herckes for loaning us the high volume air sampler.
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