HR: 09:00h
AN: B11E-05 INVITED    [Abstracts]
TI: Spatial Variability in Instantaneous Photosynthetic Carbon and Oxygen Isotope Discrimination
AU: * Barbour, M M
EM: barbourm@landcareresearch.co.nz
AF: Landcare Research, PO Box 40 Gerald St, Lincoln, 7640, New Zealand
AB: Stable carbon and oxygen isotope ratios of CO₂ are useful tracers in studies of carbon and water cycling between the terrestrial biosphere and the atmosphere. Interpretation of variation in ¹³CO₂ and C¹⁶O¹⁸O relies on models describing physical and biochemical processes and their associated fractionations. A layer of complexity not currently quantified or accounted for in canopy models is spatial variation in photosynthetic discrimination within a single leaf. A new measurement technique, employing tunable diode laser absorption spectrometry coupled to an open gas exchange system, enables online measurement of photosynthetic discrimination at high temporal resolution. Using this system, photosynthetic ¹³C and ¹⁸O discrimination was measured along leaves of a C₃ monocot. For the forage cereal Triticale, ¹³C discrimination increased by 2‰ and ¹⁸O by 20‰ from the base to the tip of mature leaves when measured at saturating irradiance. The increase in ¹³C discrimination was associated with an increase in the leaf internal conductance of CO₂, and ¹⁸O discrimination with carry-forward of evaporative enrichment along the leaf. When numerical averages are compared to flux- and area-weighted averages, the portion of the leaf approximately one third of the way from the base can be shown to provide the most representative area for scaling up.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting