Good Report On Biology 1020, College Name

Variable Exposure of Leaves under Sun and Shade

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Variable Exposure of Leaves under Sun and Shade 2
Abstract
We tested two different populations of leaves from the oak tree. We measured the leaf area and perimeter of shaded leaves and sun-exposed leaves from a number of samples from the same tree. We found that there were a number key differences between the two groups with shaded leaves being larger than the leaves exposed to sun. The leaves also appeared bigger. Statistics were performed and found that there was statistically significant variance between the two groups. The results are discussed in terms of how the leaf size can affect the general physiology to the tree.
Keywords: Oak, leaves, sun, shade, exposed

Variable Exposure of Leaves under Sun and Shade   3

Introduction
The leafs trees are where light is captured from the sun to perform photosynthesis. Leaves adapt their leaf shape in angle (Gilbert, 1979), size, shape, mass, anatomy and physiology (Eschrich, 1989). These changes in leaf mass has been shown to affect several factors like the maximum photosynthetic rates, stromatal conductance and the concentration of leaf nitrogen (Jones, 2006). This might differ in life stages of the tree and specifically studying leaf shape during the seedling stage may give an indication of where the tree allocates biomass (Berlyn 1998). By measuring a small sample of leaves this may allow us to further understand the idea of intercanopy plasticity whereby light can penetrate through the canopy to effect the energy carbon and water balance of individual leaves (Sack, 2006). In this study we are looking at the leaf size in two conditions: shade and sunlight. We hypothesize that the leafs where the sun shines less (shaded area) have optimized their surface area to receive maximal photosynthetic rates than the leaves in the sun exposed area of the tree. Although these results might depend on a number of factors like tree age and differences in drought patterns (Gottchalk, 1994). Our null hypothesis is that the means between the shaded and sunexposed leaves are exactly the same.

Materials and Methods

Leaves were collected from the oak tree (Quercus rubrica) during the early March. A total of 32 leaves (16 from the shaded part of the tree and 16 from the part that receives sunlight) from the same oak tree were collected. The leaves were flattened on a piece of paper and measured and pictures were taken with a camera directly after collecting the leaves to ensure that there was no shrinkage from water loss. The leaves were measured from the stem to the other end as well as the width of the longest edge. ImageJ (NIH, Baltimore, Maryland) was used to ImageJ to calculate the Area, Perimeter of the sun and shade exposed leaves as well as the ratio of Perimeter to Area (P:A) (Schneider, 2012) was used to process the images for the two different .
Statistical analysis of the mean, variance and standard deviation were done on both sets of leaves tested. The differences in leaf size were investigated with the analysis of variance (Excel). For each measure we tested the main differences among the two different groups. The samples were pooled and analyzed at the 5% significance level using a standard paired t test. We used linear constraints to determine whether there was a difference in the leaf size between the two groups. measured the probability that the shaded leaves would be smaller in size as compared to the leaves that had sunlight. A student t test was performed to test the hypothesis. The area and perimeter were taken and the ratio of the area and perimeter were calculated.

Results

We looked only at the size of the leaves and measured the area and perimeter using the image handling software. The leaves found in the shaded region (Figure 1) of the tree were larger in both length and width than the sun exposed leaves (Figure 1 right panel). Overall the shaded leaves had a larger mean area (Figure 2 left panel) and mean perimeter (Figure 2 center panel) than the sun exposed leaves. The mean area was double for the unshaded over the sun exposed. The perimeter area ratio was significantly larger in the shade exposed leaves. We wanted to measure whether the results were statistically significant so we conducted a student t-test. The variance between the sun exposed and shade exposed leaves was large. In an independent t-test we found that the numbers with a p-value and the difference between the two conditions are significant at a 5% level. All the results can be found in the appendix and the key results are shown in the Table 1. The standard deviation in the shaded tree was much higher for the area and perimeter measurements.

Discussion

Measuring leaf area can give insight into a lot of the physiology of the plant and can give insight into canopy plasticity. Leaf area is a well used characteristic to study leaf traits and is not species specific. Biologists can use this to estimate a reproductive strategies in the a particular plant.
In our study there was a large difference associated between the two groups. Shade affected leaf area significantly as p<0.05 in the two sample group. Specifically, in oak trees the shade does affect the may affect the leaves at different stages of grown and under different stress conditions (Gottchalk, 1994). In Gottchalk (1994) research the leaf size decreased with shade. Changes in leaf area are observed during drought as the decreasing the leaf size and surface area means less water will be lost (Marron, 2003). There may be an optimal leaf size depending on the environment (Parkhurst, 1972).
The results from this study could be utilized if one were to conduct a similar study. Doing a multi-variant analysis with other parameters like roots size and leaf weight as well as sunlight and rain could give interesting results to understand how the leaf size might affect the oak. The plant might have adapted a canopy plasticity so that all the upper leaves where sun shines are smaller (and efficiently absorb more like) and the lower leaves need to be bigger in order to maintain the same level of light absorption.

Conclusion

We measured leaves from the oak tree under two different conditions. The two different conditions were statistically significant. For this particular oak tree the shaded leaves were much larger in size than the leaves that received more sun. Although one could make a prediction and hypothesize about the leaf size it is difficult and premature after only one sampling year on fully grown oak.
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References

Ashton, P. M. S., Yoon, H. S., Thadani, R., & Berlyn, G. P. (1999). Seedling leaf structure of New England maples (Acer) in relation to light environment. Forest science, 45(4), 512-519.
Bohning, R. H., & Burnside, C. A. (1956). The effect of light intensity on rate of apparent photosynthesis in leaves of sun and shade plants. American journal of botany, 557-561.Mc
Eschrich, W., Burchardt, R., & Essiamah, S. (1989). The induction of sun and shade leaves of the European beech (Fagus sylvatica L.): anatomical studies. Trees, 3(1), 1-10.
Givnish, T. J. (1988). Adaptation to sun and shade: a whole-plant perspective. Functional Plant Biology, 15(2), 63-92
Gottschalk, Kurt W. "Shade, leaf growth and crown development of Quercus rubra, Quercus velutina, Prunus serotina and Acer rubrum seedlings." Tree Physiology 14.7-8-9 (1994): 735-749.
Jones, T. A., & Thomas, S. C. (2007). Leaf-level acclimation to gap creation in mature Acer saccharum trees. Tree physiology, 27(2), 281-290.
LEI, T. T., & LECHOWICZ, M. J. (1998). Diverse responses of maple saplings to forest light regimes. Annals of Botany, 82(1), 9-19.
Marron, N., Dreyer, E., Boudouresque, E., Delay, D., Petit, J. M., Delmotte, F. M., & Brignolas, F. (2003). Impact of successive drought and re-watering cycles on growth and specific leaf area of two Populus× canadensis (Moench) clones,‘Dorskamp’and ‘Luisa_Avanzo’. Tree physiology, 23(18), 1225-1235.
Millen, G. G., & Mc Clendon, J. H. (1979). Leaf angle: an adaptive feature of sun and shade leaves. Botanical Gazette, 437-442.
Parkhurst, D. F., & Loucks, O. L. (1972). Optimal leaf size in relation to environment. The Journal of Ecology, 505-537.
Sack, L., Melcher, P. J., Liu, W. H., Middleton, E., & Pardee, T. (2006). How strong is intracanopy leaf plasticity in temperate deciduous trees?. American Journal of Botany, 93(6), 829-839.
Schneider, C. A., Rasband, W. S., & Eliceiri, K. W. (2012). NIH Image to ImageJ: 25 years of image analysis. Nature methods, 9(7), 671-675.
Figures
Figure 1 (Left Panel) Sun exposed leaves with a 5 cm scale bar. (Right panel) Shade exposed leaves.
Figure 2 (Top Panel) Mean Area of Sun exposed (blue) and Shade exposed (red); (Center Panel ) Mean Perimeter of Sun exposed (blue) and Shade exposed (red) (Bottom Panel) Area perimeter ratio sun exposed (blue) and shade exposed (red)