PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Influences of sap flow and respiratory activity on CO₂ efflux from woody stems in a New Zealand podocarp forest.

Bowman, William ¹, Barbour, Margaret², Tissue, David ³, Turnbull, Matthew ⁴, Whitehead, David², Griffin, Kevin ¹, ¹ Columbia University:, New York City, New York, USA² Landcare Research:, Lincoln, New Zealand³ Texas Tech University:, Lubbock, Texas, USA⁴ University of Canterbury:, Christchurch, New Zealand

ABSTRACT- Measurements of CO₂ efflux from woody stems and branches were collected for Dacrydium cupressinum, the dominant species in a podocarp-broadleaf forest in south Westland, New Zealand. An automated, multi-chambered system was utilized to make continuous measurements on the stems of nine trees for up to 160 hours and on canopy branches for 24 hours. Temperature-normalized CO₂ efflux rates from stems ranged from 0.51mol m^-2 s^-1 to 2.43 mol m^-2 s^-1, while respiration rates from branches were generally larger, between 0.72 mol m^-2 s^-1 to 6.8 mol m^-2 s^-1. CO₂ efflux rates were largely predictable from sapwood temperature; however, efflux rates were lower than predicted from temperature alone during periods of maximum sapflow. This indicates that CO₂ may be transported in the xylem transpirational stream from respiring tissues in woody stems to the canopy. The measurements of CO₂ efflux were also analyzed with respect to wood density, cambial and sapwood respiratory activity, and tissue nitrogen content. The results of this study highlight the importance of considering CO₂ efflux from woody stems as a function of both the activity of the respiring tissues within stems and the barriers to diffusion for CO₂ that exist between the source tissues and the atmosphere.

Key words: Sapwood, Stem respiration, Sap flow, Dacrydium cupressinum