Document: LUI-3-59-20

Soil CO₂ efflux and soil CO₂ profile concentrations under old-growth tropical rain forest

SCHWENDENMANN, L.* ¹, E.VELDKAMP ¹, T.BRENES ², J.MACKENSEN ¹, D.A.CLARK ³, D.B.CLARK ³ and S.F.OBERBAUER ⁴

University of Goettingen, 37077 Goettingen, Germany ¹
La Selva Biological Station, Puerto Viejo, Costa Rica ²
University of Missouri-St.Louis, Missouri 63121, USA ³
Florida International University, Miami, FL 33199, USA ⁴

Abstract:
Estimates of carbon fluxes in tropical forests are important in the current discussion on the world's carbon balance of forests. The main objectives of this study are (i) to present results on the soil CO₂ efflux and soil CO₂ concentration under old-growth tropical rainforest in the Atlantic zone of Costa Rica and (ii) to describe the interactions between soil CO₂ efflux, soil moisture content and soil temperature. We measured CO₂ efflux from 48 soil chambers in six plots (covering Inceptisols and Ultisols) bi-weekly since March 1998 using an infrared CO₂ analyzer. At the same time we measured soil CO₂ concentrations at 5, 20, 40, 75, 150, 250 and 350 cm depth using a GC. At the Inceptisol sites, soil CO₂ efflux rates ranged from 10.4 to 11.7 Mg CO₂-C ha^-1 yr^-1. Significantly higher flux rates occurred in the less fertile Ultisols where efflux rates ranged between 12.4 to 15.8 Mg CO₂-C ha^-1 yr^-1. When the volumetric soil moisture content of Inceptisols and Ultisols was > 0.50 at 5 cm depth, there was a negative correlation (r = -0.7) between soil CO₂ efflux and soil moisture. Higher soil CO₂ concentrations in the upper soil profile under moist conditions (up to 2 % in Inceptisols) supports the idea that higher soil moisture contents partially inhibit CO₂ diffusion to the soil surface. The correlation between soil temperature at 5 cm depth and CO₂ efflux was around r = 0.4. As there was also a correlation between soil moisture content and soil temperature (r = -0.3) it was difficult to explain changes in soil CO₂ efflux using these factors only.

Keywords: CO₂ efflux, tropical forest, soil moisture content, soil temperature

This abstract is being presented at: 9:45 AM in session:
Oral Session #25: Organic Matter Dynamics in Ecosystems.