Elevated [CO2] changes soil organic matter composition and substrate diversity in an arid ecosystem

Journal Article · Thu Nov 15 00:00:00 EST 2018 · Geoderma

DOI:https://doi.org/10.1016/j.geoderma.2018.05.025· OSTI ID:1545059

Tfaily, Malak M.  ^[1]; Hess, Nancy J.  ^[1]; Koyama, Akihiro ^[2]; Evans, R D. ^[3]

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1. BATTELLE (PACIFIC NW LAB)
2. Algoma University
3. Washington State University

Little is known about how rising atmospheric [CO2] will impact long-term plant biomass or the dynamics of soil organic matter (SOM) in arid ecosystems. Evans et al. (1) reported higher soil organic carbon (SOC) and total nitrogen (N) concentrations following 10 years exposure to elevated atmospheric [CO2] at the Nevada Desert Free-Air-Carbon dioxide-Enrichment (FACE) Facility (NDFF). In this study, we investigated potential mechanisms that resulted in increased SOC and total N accumulation and SOM stabilization using high resolution mass spectrometry. Samples were collected from soil profiles to 1 m in depth with a 0.2 m increment under the dominant evergreen shrub Larrea tridentata. The differences in the molecular composition and diversity of SOM were more evident in surface soils and declined with depth, and were consistent with higher SOC and total N concentrations under elevated than ambient [CO2]. Our molecular analysis also suggested increased root exudation and/or microbial necromass from stabilization of labile C and N contributed to SOM and N stocks. Increased microbial activity and metabolism under elevated [CO2] compared to ambient treatments suggest that elevated [CO2] altered microbial carbon use patterns, reflecting changes in the quality and quantity of SOC inputs. We found that plant-derived compounds were primary substrates for microbial activity under elevated [CO2] and microbial products were the main constituents of stabilized SOM. Our results suggest that arid ecosystems are a potential large C sink under elevated [CO2], given the extensive coverage of the land surface, and that labile compounds are transformed to stable SOM via microbial processes. Arid systems are limited by water, and thus may have a different C storage potential under changing climates than other ecosystems that are limited by nitrogen or phosphorus.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1545059
• Report Number(s): PNNL-SA-129666
• Journal Information: Geoderma, Vol. 330
• Country of Publication: United States
• Language: English