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Mathematical Biology seminar
Dave Bowling
Biology Department, University of Utah
"Photosynthetic and respiratory fluxes and their isotopic content in a Colorado s ubalpine forest"
November 12
3:05pm in LCB 225
The isotopic characteristics of whole-ecosystem photosynthesis and
respiration were examined at a high-elevation coniferous forest (the
Niwot Ridge AmeriFlux site). A tunable diode laser spectrometer was
used to monitor concentrations and carbon isotope ratios (d13C) of CO2
within the canopy, every 6 minutes for 3 months during summer
2003. CO2 fluxes were measured using the eddy covariance technique,
and atmospheric boundary layer stability was assessed using
within-canopy wind and temperature profile measurements. Net ecosystem
exchange of CO2 during July 2003 varied from uptake of -10 to release
of 5 mmol C m-2 d-1. The carbon isotope ratio of ecosystem respiration
(d13CR, calculated using Keeling plots) at night (9pm - 4 am) varied
from -26.9 to -25.3 . Changes from one night to the next were small
(0.5 maximum), but multi-day trends with consistent directional
changes were apparent. d13CR calculated at inlet heights below 2 m
varied compared to those within the vegetation canopy (7-14m) by as
much as 2.2 on the same night, indicating different isotopic content
in the foliar and soil respiratory fluxes. Daytime calculations of
Keeling plot intercept (reflecting the combined influence of
photosynthesis and respiration) varied from -26.9 to -24.5 and were
generally uncorrelated with nighttime values. Nocturnal d13CR varied
from the daytime values several hours earlier by as much as 2.0
. These data suggest large temporal isotopic disequilibrium may exist
between the photosynthetic and respiratory fluxes. The possibility of
directly measuring the isotope disequilibrium via this approach will
be explored.
For more information contact J. Keener, 1-6089
E-mail:
keener@math.utah.edu
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