Document: SIG-3-59-45

Nitrogen-fixing tropical trees sequester soil carbon.

RESH, S.C.* ¹ and D.BINKLEY ²

CSIRO Forestry and Forest Products, TAS Australia ¹
Colorado State University, Fort Collins, CO, USA ²

Abstract:
Anthropogenic increases in nitrogen inputs may enhance terrestrial carbon sequestration through increased plant production. The increase in nitrogen supply may also affect soil carbon sequestration through altered decomposition. We examined soil carbon pools under tropical plantations of nitrogen-fixing tree species and Eucalyptus that replaced agricultural land use. Using stable carbon isotopes, we tracked the loss of old soil organic carbon from the previous C₄ land use (SOC₄) and the gain of new soil organic carbon from the C₃ forest plantations (SOC₃). We found 0.06 kg C₄ m^-2 yr^-1greater retention of the old, agricultural soil carbon and 0.05 kg C₃ m^-2 yr^-1greater new carbon accretion under the N-fixers relative to Eucalyptus. Both the greater old carbon retention and greater new carbon accretion corresponded with nitrogen accretion (P < 0.01). The effect of increased nitrogen supply on soil carbon retention may be an important mechanism of carbon sequestration that is not currently considered in global change research.

Keywords: carbon accretion, carbon retention, carbon sequestration, Eucalyptus, isotopes, nitrogen-fixing trees, soil organic carbon

This abstract is being presented at: 2:30 PM in session:
Oral Session #52: Carbon Storage in Ecosystems.