Ecological Interpretation of Leaf Carbon Isotope Ratios: Influence of Respired Carbon Dioxide
1989
In a Neotropical moist forest at Barro Colorado Island, Panama, °¹ ³C values of CO₂ in air and °¹ ³ values of leaf tissue exhibit parallel patterns of variation between the forest floor and the canopy. During the daytime, °¹ ³C values of CO₂ from air sampled at 1 m and 0.5 m were significantly less than that at 25 m. Based on mass balance equations, up to 18% of the CO₂ in air at 0.5 m above the forest floor is from respiration. Respired CO₂ is responsible for 31 and 37% of the variation in isotope composition in leaves of two species of herbaceous bamboo grown in a well—ventilated sun treatment and in the forest understory. Respired CO₂ accounts for 45—70% of the difference in °¹ ³C values between understory and canopy leaves for three species growing in large—scale irrigation and control treatments. Understory leaves of these species show °¹ ³ values consistent with higher ratios of intercellular to ambient CO₂ in irrigated relative to control treatments. Estimates of water—use efficiency from leaf carbon isotope content should be corrected for the contribution of the carbon isotope composition of respired CO₂ in closed—canopy forests.
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