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- Title
Predicting daytime carbon isotope ratios of atmospheric CO2 within forest canopies.
- Authors
Buchmann, N.; Brooks, J.R.; Ehleringer, J.R.
- Abstract
1. While measurements of leaf carbon isotope ratios ([sup 13]C/[sup 12]C) in terrestrial ecosystems have become more frequent, interpreting these data can remain a challenge in well developed canopies: the variation in leaf δ[sup 13]C (δ[sup 13]C[sub p]) values is influenced by both the variation in δ[sup 13]C of source air (δ[sup 13]C[sub a]) and by photosynthetic carbon isotope discrimination (Δ). However, source air information is often unavailable, limiting the interpretation of δ[sup 13]C[sub p], particularly in dense stands. 2. In this synthesis we found that about 70% of the observed variation in δ[sup 13]C[sub p] values within the canopy was influenced by changes in Δ, and that about 30% was determined by source air effects. Significant shifts in δ[sup 13]C[sub a] occur in canopies with high leaf area, predominantly within 1 m above the forest floor. In complex canopies, particularly in the understorey, source air effects cannot be neglected if δ[sup 13]C[sub p] measurements are used to calculate Δ and c[sub i]/c[sub a] ratios [ratio of internal CO[sub 2] concentration in the mesophyll airspaces (c[sub i]) to the ambient atmospheric concentration of CO[sub 2] (c[sub a])]. 3. We modelled δ[sup 13]C[sub a] of daytime source air for deciduous and coniferous forests in boreal, temperate and tropical biomes. An inverse regression model with easily available input variables accounted for about 90% of the variation in daytime δ[sup 13]C[sub a] values throughout the canopy. 4. In open canopies with leaf area index (L) of <2.5 or at canopy heights ≥1 m, the within-canopy daytime δ[sup 13]C[sub a] differences are negligible, and variations in δ[sup 13]C[sub p] are associated primarily with changes in Δ. Then, one can use the easily available carbon isotope ratio of the troposphere (δ[sup 13]C[sub trop]) as a substitute for δ[sup 13]C[sub a] to calculate...
- Subjects
CARBON isotopes; ATMOSPHERIC carbon dioxide; FOREST canopies
- Publication
Functional Ecology, 2002, Vol 16, Issue 1, p49
- ISSN
0269-8463
- Publication type
Article
- DOI
10.1046/j.0269-8463.2001.00591.x