ARS | Publication request: Acclimation of Photosynthesis in Leaves of Sour Orange Trees Grown at Elevated Co2 for 14 Years.

Submitted to: New Phytologist
Publication Acceptance Date: March 31, 2004
Publication Date: August 1, 2004
Citation: Adam, N.R., Wall, G.W., Kimball, B.A., Idso, S.B., Webber, A.N. 2004. Acclimation Of Photosynthesis In Leaves Of Sour Orange Trees Grown At Elevated Co2 For 14 Years.. New Phytologist. 163:341-347

Interpretive Summary: Understanding how slow-growing perennial trees will be affected by future increasing levels of carbon dioxide after a period of years or decades is crucial to understanding the future impact of global climate change. Photosynthesis and biomass production have been monitored on sour orange trees growing under an enhanced carbon dioxide atmosphere and in well-fertilized soil for 14 years. In recent years, the extent of CO2-induced enhancement of photosynthesis declined from 184% in 1991 (second year) to 28% in 2001. Over the same time span, the enhancement of annual wood biomass increment declined from 184% to 78%. In the 14th year, the lowered photosynthesis enhancement was shown to be due to a decrease in the content of the primary CO2-fixing enzyme, and thus a decrease in the capacity of photosynthesis. This finding indicates that long-term growth at elevated CO2 can result in a reduction of photosynthesis in perennial trees, even when nitrogen is non-limiting. Ecological modelers can use this information to help model the likely long-term effects of elevated CO2 on the growth of trees in the future. This research will also benefit future consumers and growers of citrus products because it enables strategies and plans to be made to cope with future changes in citrus productivity.

Technical Abstract: Perennial trees are a major carbon sink on a global scale, accounting for approximately two-thirds of terrestrial carbon fixation. Understanding how slow-growing perennial trees will be affected by future increasing levels of carbon dioxide after a period of years or decades is crucial to understanding the future impact of global climate change. Photosynthesis and biomass production of sour orange trees growing under an enhanced carbon dioxide atmosphere and in nitrogen replete soil has been monitored for 14 years. In recent years, the extent of CO2-induced enhancement of photosynthesis declined from 184% in 1991 (second year) to 28% in 2001. Over the same time span, the enhancement of annual wood biomass increment declined from 184% to 78%. From measurements made in the 14th year, the lowered photosynthesis enhancement was shown to be due to a decrease in the maximum rate of CO2 fixation (Vcmax), and to a lower activity and content of the primary CO2-fixing enzyme ribulose-1,5,-bisphosphate carboxylase/oxygenase (Rubisco). This finding indicates that long-term growth at elevated CO2 can result in down regulation of photosynthesis in perennial trees, even when nitrogen is non-limiting.