Photosynthetic down‐regulation over long‐term CO2 enrichment in leaves of sour orange (Citrus aurantium) trees
2004
Adam, Neal R. | Wall, Gerard W. | Kimball, Bruce A. | Idso, Sherwood B. | Webber, Andrew N.
• Understanding how trees are affected by a long‐term increase in atmospheric CO₂ is crucial to understanding the future impact of global climate change. Measurements of photosynthetic characteristics were made in sour orange trees (Citrus aurantium) growing under an enhanced CO₂ atmosphere and N‐replete soil for 14 yr to determine whether photosynthetic down‐regulation had occurred. • Photosynthesis, A : Cᵢ gas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment. The CO₂‐induced enhancement ratio of photosynthesis was calculated and compared with estimates of the enhancement of cumulative wood biomass production. • Content of the large subunit of Rubisco was significantly reduced by CO₂ enrichment indicating that down‐regulation had occurred. A high correlation between the CO₂‐induced enhancement of photosynthesis and the enhancement of cumulative wood biomass production suggested that the decline in wood biomass production was closely related to the decline in photosynthesis. • These results indicate that long‐term CO₂ enrichment can result in photosynthetic down‐regulation in leaves of trees, even under nonlimiting N conditions.
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