Net mineralization of N at deeper soil depths as a potential mechanism for sustained forest production under elevated [CO2]

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Global Change Biology

DOI:https://doi.org/10.1111/j.1365-2486.2010.02240.x· OSTI ID:1001718

Iversen, Colleen M ^[1]; Hooker, Toby ^[2]; Classen, Aimee T ^[3]; Norby, Richard J ^[1]

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1. ORNL
2. Utah State University (USU)
3. University of Tennessee, Knoxville (UTK)

Elevated atmospheric [CO2] is projected to increase forest production, which could increase ecosystem carbon (C) storage. However, sustained forest production will depend on the nutrient balance of the forested ecosystem. Our aim was to examine the causes and consequences of increased fine-root production and mortality throughout the soil profile under elevated CO2 with respect to potential gross nitrogen (N) cycling rates. Our study was conducted in a CO2-enriched sweetgum (Liquidambar styraciflua L.) plantation in Oak Ridge, TN, USA. We used isotope pool dilution methodology to measure potential gross N cycling rates in laboratory incubations of soil from four depth increments to 60 cm. Our objectives were two-fold: (1) determine whether N is available for root acquisition in deeper soil, and (2) determine whether increased inputs of labile C from greater fine-root mortality at depth under elevated [CO2] had altered N cycling rates. While gross N fluxes declined with soil depth, we found that N is potentially available for roots to access, especially below 15 cm depth where microbial consumption of mineral N was reduced. Overall, up to 60% of potential gross N mineralization, and 100% of potential net N mineralization, occurred below 15-cm depth at this site. This finding was supported by in situ measurements from ion-exchange resins, where total inorganic N availability at 55 cm depth was equal to or greater than N availability at 15 cm depth. While it is likely that trees grown under elevated [CO2] are accessing a larger pool of inorganic N by mining deeper soil, we found no effect of elevated [CO2] on potential gross or net N cycling rates. Thus, increased root exploration of the soil volume under elevated [CO2] may be more important than changes in potential gross N cycling rates in sustaining forest responses to rising atmospheric CO2.

• Research Organization: Oak Ridge National Laboratory (ORNL); Oak Ridge National Environmental Research Park
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1001718
• Journal Information: Global Change Biology, Journal Name: Global Change Biology Journal Issue: 2 Vol. 17; ISSN 1354-1013
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AVAILABILITY
CARBON
DILUTION
ECOSYSTEMS
EXPLORATION
FORESTS
ION EXCHANGE
MINERALIZATION
MINING
MORTALITY
NITROGEN
NUTRIENTS
PRODUCTION
RESINS
SOILS
STORAGE
TREES
elevated [CO2]
fine roots
isotope pool dilution
potential gross N mineralization
soil depth
sweetgum