PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Scaling photosynthesis from shoots to the canopy in a rimu dominated rainforest in New Zealand.
Tissue, David*,1, Turnbull, Matthew2, Griffin, Kevin3, Barbour, Margaret4, Hunt, John4, Schuster, William5, Brown, Kim6, Whitehead, David4, 1 Texas Tech University, Lubbock, TX2 University of Canterbury, Christchurch, New Zealand3 Columbia University, Palisades, NY4 Landcare Research, Lincoln, New Zealand5 Black Rock Forest Consortium, Cornwall, NY6 Ohio University, Athens, OH
ABSTRACT- Our objective was to determine the potential for estimating CO2 exchange in a complex, mixed species, natural rainforest in New Zealand using photosynthetic and internal CO2 (Ci) measurements taken at different scales. Our study site is representative of an extensive multi-layered, mixed conifer-broadleaved forest ecosystem in South Westland, that is dominated by rimu (Dacrydium cupressinum). The forest receives high rainfall (3.2 m), has highly leached and nutrient poor soils, and exhibits low productivity. Carbon exchange in this forest is sensitive to small shifts in climate, including temperature, cloudiness and periods of seasonal water deficit. We used direct measurements of leaf photosynthesis (ACicurves) to estimate potential limiting factors to photosynthesis (e.g. Vcmax and Jmax). We used the Leuning coupled photosynthesis-stomatal conductance model to estimate a shorter-term value of Ci at the leaf level, which was tested against direct longer-term estimates of Ci based on delta 13C isotope discrimination in leaves measured at different heights through the canopy. These results were compared with longer-term whole ecosystem Ci values estimated using Keeling plots (i.e. measurements of delta 13C discrimination in air samples taken at different heights through the canopy). Decreasing values of Ci with increasing height in the canopy indicate higher rates of photosynthesis (confirmed by gas exchange measurements) at higher light levels. Although photosynthesis is limited by light availability, the primary limitation to photosynthesis in these forest trees appears to be low nutrient availability that greatly reduced biochemical capacity (i.e. Vcmax and Jmax). In general, there was good agreement between the three estimates of Ci suggesting that scaling CO2 exchange from the shoot to the canopy level is possible in this forest using a multi-layered model based on shoot-level photosynthesis.
Key words: photosynthesis, Dacrydium cupressinum, scaling, stable isotopes