Sustainability and environmental enhancement in changing circumstances

Elevated CO2 changes the moderate shade tolerance of yellow birch seedlings



Received August 20, 2006,Revised November 24, 2006, Accepted , Available online

Volume 19,2007,Pages 502-507

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To demonstrate the existence of light thresholds in plant growth and to examine the e ects of elevated CO2 on the shade tolerance of a tree species, an experiment consisting of a completely randomized design for a total of 96 yellow birch (Betula alleghaniensis Britton) seedlings was conducted with 3 light levels (2.9%, 7.7%, 26.1% of full sunlight) 2 CO2 levels (350 and 700 10 ppm) with 4 replications in a phytotron. The study proved that thresholds exist and they vary in di erent plant organs. In ambient CO2, the thresholds were 13.3%, 18.7%, 15.0%, 15.2%, and 15.6% of full sunlight for stem, leaf, root, total plant biomass, and the averaged value, respectively. In 700 ppm CO2, the corresponding thresholds were 16.7%, 21.3%, 18.1%, 21.7% and 19.5% for stem, leaf, root, total plant biomass, and the averaged value, respectively. The lowest threshold in the stem is an indicator of the minimal light intensity for regular growth for seedlings of this species. Below this threshold, light-stressful growth occurs. The result of a paired t-test indicated that the thresholds in elevated CO2 were significantly higher than in ambient CO2. This suggests that yellow birch will lose its moderate shade tolerance, evolutionally becoming a shade-intolerant species, and that it may become more di cult to naturally regenerate in the future.

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