Vegetation effects on the isotopic composition of atmospheric CO2 at local and 
regionl scales: theoretical aspects and a comparison between rain forest in 
Amazonia and a boreal forest in Siberia

Lloyd, J.; Kruijt, B.; Hollinger, D. Y.; Grace, J.; Francey, R. J.; Wong, S.-C.; Kelliher, F. M.; Miranda, A. C.; Farquahr, G. D.; Gash, J. H. C.; Vygodskaya, N. N.; Wright, I. R.; Miranda, H. S.; Schulze, Ernst Detlef

doi:10.1071/pp9960371

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Vegetation effects on the isotopic composition of atmospheric CO₂ at local and regionl scales: theoretical aspects and a comparison between rain forest in Amazonia and a boreal forest in Siberia

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Citation

Lloyd, J., Kruijt, B., Hollinger, D. Y., Grace, J., Francey, R. J., Wong, S.-C., et al. (1996). Vegetation effects on the isotopic composition of atmospheric CO₂ at local and regionl scales: theoretical aspects and a comparison between rain forest in Amazonia and a boreal forest in Siberia. Australian Journal of Plant Physiology, 23(3), 371-399. doi:10.1071/pp9960371.

Cite as: https://hdl.handle.net/21.11116/0000-0004-8AA0-B

Abstract

In order to understand the factors influencing the isotopic composition of air above and
within plant canopies, equations quantifying the effects of photosynthesis, respiration and turbulent
transport on the isotopic composition of the surrounding CO, are developed. These equations are then
extended to the regional scale, allowing the average isotopic composition of CO, within the convective
boundary layer to be related to the isotopic composition of tropospheric C0, and to isotopic
fractionations during ecosystem carbon exchange. Equations presented have the potential to be inverted,
allowing direct estimation of isotopic fractionations by vegetation at the local and regional scales.
Equations allowing the estimation of the extent of refixation of respired CO, ('recycling') at the regional
scale are also presented.
Using measurements of CO, carbon isotopic composition in conjunction with ecosystem flux
measurements, the theory is applied to a tropical rain forest in Amazonia and a boreal forest in Siberia.
When examined on a ground area basis and over the course of a day it is observed that, by virtue of
greater fluxes but similar isotopic fractionations, the tropical rainforest exerts much more influence over
the isotopic composition of the surrounding air than does the boreal forest. Due to higher rates of
ecosystem respiration, recycling of respired C02 is modelled to be much greater for tropical rainforest,
but values presented here are considerably lower than previously published estimates, the latter being
based solely on the relationship between the isotopic composition and concentrations of C02 within forest canopies. The reasons for these differences are examined.