Shade intolerance in plants and response to elevated carbon dioxide
LE3 .A278 2012
Bachelor of Science
Environmental & Sustainability Studies
Carbon dioxide (CO2) levels in the atmosphere have been rising due to anthropogenic fossil fuel use and land clearing practices. One of the potential impacts of increasing CO2 will be upon plants. CO2 is an input in the photosynthetic process and has a direct impact on the ability of plants to grow. However, it is well known that the extent to which photosynthesis increases in response to elevated CO2 varies with the level of competition. Changes in plant allocation occur when plants compete for available light through a process known as the shade avoidance response. A low red:far red ratio (R:FR) causes shade intolerant plants to rise above competing plants by allocating energy to stem elongation at the expense of leaves, storage organs, and roots. It was hypothesized that because the shade avoidance response takes resources away from the roots, it will decrease overall nutrient uptake so that photosynthesis will not be able to respond as positively to increased CO2 levels. This was tested using four genetic lines of Arabidopsis thaliana: a mutant with an enhanced shade avoidance response (PB genetic line), a mutant with a reduced shade avoidance response (PA genetic line) and their corresponding wild types. The plants were grown in chambers at both ambient (380 ppm) and elevated (760 ppm) CO2 under conditions that mimicked shade (low R:FR) and full sun (high R:FR). It was found that all lines experienced a greater growth response to elevated CO2 at a high R:FR than at a low R:FR. However, no differences were found among the genetic lines in their response to elevated CO2. This suggests that differences in allocation were not responsible for the greater growth response to elevated CO2 at a high R:FR. Rather, there may be a direct effect of light quality on the response of photosynthesis to elevated CO2.
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