|Allen, Leon - Hartwell|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2008
Publication Date: 2/7/2009
Citation: Allen Jr, L.H., Vu, J.C. 2009. Carbon dioxide and high temperature effects on growth of young orange trees in a humid, subtropical environment. Agricultural and Forest Meteorology. 149:820-830.
Interpretive Summary: Rising atmospheric carbon dioxide (CO2) and global warming could impact growth of citrus trees. Less research has been conducted on this important fruit crop than other crops and forests. Also, few studies of impacts of dry air (technically defined as vapor pressure deficit) on citrus photosynthesis and growth have been made. Agricultural Research Service scientists at Gainesville, Florida compared the effects of elevated CO2 with ambient CO2 on young Ambersweet orange trees grown in containers in two temperature-gradient greenhouses at either 720 or 360 PPM CO2. Each greenhouse had 4 zones that increased by +2.7 degrees F from zone to zone above ambient temperatures. The increase from zone 1 to zone 4 was 8.1 degrees F. Elevated CO2 increased tree growth by 37% the first year and 17% for the second year. Higher temperatures increased growth slightly. In contrast, an earlier study of young citrus trees at Phoenix, Arizona showed more than 100% increases in growth response to elevated CO2. High vapor pressure deficit appears to cause remarkably low photosynthesis in citrus at ambient CO2 compared to elevated CO2 in the hot midlatitude desert climate of Phoenix, but this effect was not found in the humid subtropical climate of Gainesville.
Technical Abstract: Rising atmospheric carbon dioxide (CO2) and global warming could impact growth of citrus trees. To measure CO2 and temperature effects, ARS scientists transplanted five 2-year-old Ambersweet orange trees on Swingle citrumelo rootstock to containers in two temperature-gradient greenhouses maintained at 360 or 720 PPM CO2. Two containers were located in each of four 1.5 degree C increment zones. All growth components were different between years except leaf fresh weight and fine root biomass. Elevated CO2 increased growth except for leaves and fine roots. Biomass response ratios to CO2 (720/360) for the first and second year, respectively, were 1.00 and 1.11 for leaves, 1.57 and 1.18 for shoot wood, 1.40 and 1.19 for total roots, and 1.37 and 1.17 for total plants. The decrease in response to CO2 in the second year was due to crowding of roots and shoots. Components of shoot wood, total root, and total plant biomass increased slightly with increasing temperature. No CO2 X temperature interactions were found. Lower vapor pressure deficit was discussed as the main reason for much lower citrus responses to elevated CO2 in this warm humid subtropical environment than was found earlier in the hot midlatitude desert environment of Phoenix, Arizona.