Photosynthesis in Different Colored Leaves

By: John Thrasher, Jamie Savant, and Walker Phillips

We tested the photosynthetic rates of leaves with varying levels of chloroplast. During fall, the breakdown of chloroplasts causes the change in the color of leaves eventually causing the leaf to die, which leads us to hypothesize that as the chloroplast breaks down in leaf the photosynthetic rate will decrease.

To test our hypothesis we placed three different colored leaves into gas chambers connected to a CO2 probe. In each trial we exposed each leaf to 6 minutes of light and then 6 minutes of dark. We ran 2 trials for each color using different leaves for each trial. Leaves change color in autumn because of the deteriorating of chloroplasts. Since the chloroplast is directly related to photosynthesis we predicted that different color leaves have different levels of chloroplast which will lead to a slower rate of photosynthesis. Our results showed that the rate of photosynthesis was higher in green leaves than in the yellow and red leaves. The Average rate of photosynthesis for green leaves is -9.3115 ppm CO2 /min*g. The average rate for yellow leaves is -8.391 ppm CO2/min*g. The average rate for red leaves was -1.6355 ppm CO2/min*g. We ran an ANOVA test, a one way analysis of variance and obtained a p value of 0.15744 showing that our results were not significant. Our results are consistent with the predictions we made, however the leaves were taken off the trees several hours prior to experimentation. One proposed solution to this problem is taking the leaf from the tree and beginning the experiment as soon as possible. Another potential problem we incurred was sample size. With the small sample size we used, there is a possibility that obtained leaves differentiating from the norm. A solution to this problem is to increase the size vastly. The results from Velikova et al. 2008 show that in Eucalyptus leaves, younger leaves did not match older leaves in rates of photosynthesis in elevated CO2 environments. Martinez 2008 showed that senescence occurs when autumn leaves fall off of the tree, as well as showing that when the chloroplast breaks down, it is an interruption of Photosystem II, and subsequently isolated chloroplasts cleave off Rubisco. During our experiment, we gained new insights about how fast leaves photosynthesize. This fact, although our data was consistent, is probably why our correlation between rate of photosynthesis and color of the leaf was insignificant.