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.
Relationships between carbon assimilation and foliar nitrogen concentration in tropical rain forest functional groups.
Domingues, Tomas*,1, Flanagan, Lawrence2, Martinelli, Luiz3, Ometto, Jean1, 3, Ehleringer, James1, 1 University of Utah, Salt Lake City, Utah, USA2 University of Lethbridge, Lethbridge, Alberta, Canada3 University of São Paulo, Piracicaba, São Paulo, Brazil
ABSTRACT- Significant correlations have been observed between maximum assimilation rate and foliar nitrogen concentration in leaves of many temperate species, largely because the nitrogen is allocated to photosynthetic activities. This assimilation-nitrogen relationship has been used to simplify a number of ecosystem-scale carbon balance models. In the present work we tested the hypothesis that carbon assimilation rates can be predicted based on leaf nitrogen content for a tropical rain forest ecosystem in Santarém (PA), Brazil. Four distinct plant functional groups were evaluated: top canopy lianas, top canopy trees, mid canopy trees and understory trees. As a functional group, trees did follow the expected linear assimilation-nitrogen relationship. The slope of the relationship shifted with season, becoming steeper during the dry season. The lianas functional group showed high foliar nitrogen concentrations, similar to those present on top canopy trees. However, high nitrogen levels in lianas did not translate into high photosynthetic capacity, placing this group below the observed assimilation-nitrogen trend line. We observed that lianas operated with significantly lower stomatal conductances, resulting in a greater stomatal limitation to carbon assimilation. Current work is being done to understand why lianas maintain high nitrogen levels on their leaves without benefiting from high assimilation levels.
Key words: carbon balance, rain forest, photosynthesis, foliar nitrogen