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United States Department of Agriculture

Agricultural Research Service

Title: Spring leaf flush in aspen (Populus tremuloides) clones is altered by growth at elevated carbon dioxide and elevated ozone

item Mcgrath, Justin
item Karnosky, David
item Ainsworth, Elizabeth - Lisa

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2009
Publication Date: 4/10/2010
Citation: McGrath, J.M., Karnosky, D.F., Ainsworth, E.A. 2010. Spring Leaf Flush In Aspen (Populus tremuloides) Clones Is Altered By Growth At Elevated Carbon Dioxide and Elevated Ozone. Environmental Pollution. 158(4):1023-1028.

Interpretive Summary: Rapid development of leaf area is important for trees competing for light and space in dense forest plantations. Understanding how climate change will impact this trait is critical to predicting forest composition in the future. In this study, we investigated how aspen clones responded to two important aspects of global climate change, rising carbon dioxide and rising ozone concentrations. Elevated carbon dioxide stimulated leaf area development, while elevated ozone had the opposite effect. Individual leaf area was not altered by elevated carbon dioxide, but photosynthesis was improved. In elevated ozone, aspen clones (genotypes) responded differently. A sensitive clone showed reduced individual leaf area, while the tolerant clone increased its leaf area when grown at elevated ozone. Understanding which clones will respond to climate change is an important aspect of forest management, and critical to predictions of how competition will change in future forests.

Technical Abstract: Early spring leaf out is important to the success of trees competing for light and space in dense forest plantation canopies. In this study, we investigated spring leaf flush and how elevated carbon dioxide concentration and elevated ozone concentration altered leaf area index development in a closed Populus tremuloides (aspen) canopy. This work was done at the Aspen FACE experiment where aspen clones have been grown since 1997 in conditions simulating the [CO2] and [O3] predicted for ~2050. The responses of two clones were compared. During the first month of spring leaf growth, trees in elevated [CO2] plots showed a stimulation of leaf area index (36 %), while trees in elevated [O3] plots had lower leaf area index (-20 %). While individual leaf area was not significantly affected by elevated [CO2], the photosynthetic operating efficiency of aspen leaves was significantly improved (51 %). There were no significant differences in the way that the two aspen clones responded to elevated [CO2]; however, the two clones responded differently to growth at elevated [O3]. The O3-sensitive clone, 42E, had reduced individual leaf area when grown at elevated [O3] ( 32 %), while the tolerant clone, 216, had larger mature leaf area at elevated [O3] (46 %). These results indicate a clear difference between the two clones in their response to elevated [O3], which could affect competition between the clones, and result in altered forest composition in future atmospheric conditions.

Last Modified: 10/18/2017
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