PARENT SESSION
Contributed Oral Session 89: Soil Ecology: Plant - Soil Relationships
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal

Partitioning heterotrophic and rhizospheric soil respiration in a mature Dougals-fir forest.

Lalonde, Rachelle^*,1, Prescott, Cindy¹, ¹ University of British Columbia, Vancouver, British Columbia, Canada

ABSTRACT- We partitioned belowground respiration to estimate a portion of CO₂ originating from heterotrophic and rhizospheric organisms. As part of the Fluxnet Canada program, we investigated heterotrophic and rhizospheric respiration rates at a 55-year-old Douglas-fir forest on Vancouver Island, British Columbia. We used a root exclusion technique with fifty cylinders, 10 cm diameter by 50 cm long, with large windows cut out on either side. Half of the cylinders had a 0.5 m nylon mesh attached to these windows to create a barrier against roots and hyphae. The cylinders were then installed, extending to below the root zone (40 cm). These cylinders provided a measure of heterotrophic respiration; rhizospheric respiration was calculated as the difference between the open and mesh cylinders. Our results indicate that heterotrophic organisms are the dominant producers of CO₂ during warmer months (June-Sept), but not during the spring and fall. Within the top 50 cm of this forest soil, 65% of the annual CO₂ is from heterotrophic respiration and 35% is from rhizospheric respiration.

Key words: soil, respiration, forest