Final 1: Soil pH and Various Factors Concerning the Trees in Oxford

This topic submitted by Carl Marsh, Jenn Swing, Jason Fox ( marshcd@muohio.edu ) on 12/16/03 .

Natural Systems 1 Syllabus---Western Program---Miami University

Proposal
Dr. Chris Meyers
December 16, 2003
Jason Fox, Carl Marsh, Jennifer Swing
Section E
Soil pH and Various Factors Concerning the Trees in Oxford
Questions:
The questions we answered in our lab is threefold:
How is the soil pH affected by the decomposition of leaves of 4 key tree species?
Does our soil contain a limestone buffer that negates any possible pH changes?
Is there any statistically significant evidence that leaf pH functions as an allelopathy, affecting seed growth, as well as inhibiting growth under our key tree species? (This will be measured directly by the number of plants growing under these species. We will also measure this indirectly by looking at seed dispersal.

Hypothesis:
Our hypothesis is to determine if there is a significant difference in the soil pH in key species of trees before and after the major leaf fall. The most significant is the White Pine (Pinus strobus), as its needles are more acidic than the leaves of the English Oak (Quercus robur), Silver Maple (Acer saccherinum), or Black Locust (Robinia pseudoacacia) trees.
Because of this difference of soil pH, there will be a lack of other species that are growing within a certain radius of the base of the tree. This difference will also have an effect on each treeÕs next generation. While seeds that fall near the tree will not be able to grow, those that fall farther away from the parent will do much better, depending on how far they travel. This cycle will then continue with the next generations.
However, should there not be a significant difference in soil pH, and our hypothesis is rejected, there is a plausible explanation. The soil may contain a measurable concentration of limestone that comes from the local bluffs in Pfeffer Park. Because of the inherent basic properties of the limestone, it would absorb the acidity from the leaf litter. Because of this limestone buffer, there would be an insignificant, if any, difference in the pH of the soil. This would in turn, affect the growth of other species around the base of the tree. There would be no difference in the next generation of trees from the seed dispersal.

Introduction:
Our experiment examined the role leaf litter plays in fluctuating ph
levels in soil and the importance of Ph, (Van Straalen) (Tansley) (Roebertson)
(Mushunsky) (Gupta) (Christenson) (Kirk) (Hedlley)(Archor) (Hirshc). Maple leaf
litter has been found to effect pH as it was used by (Bialczyk) when added to a
solution to affect pH levels in sand mediums. Also our experiment tested natural
soil buffers from limestone, which has been found to decrease the sway acids and
bases have on soil and sand pH levels (Van Straalen). Like allelopathic plants that
drop chemicals to poison competition, trees drop their leaves and if their litter
fluctuates the pH of the soil, may also act as an allelopath. Leaf litter, after it
reaches the ground, decomposes. This decomposition occurs partly from
nitrification. Nitrification influences nutrient uptake and plant growth as well as
pH. This extra N added to the soil surrounding the tree may act as an allelopathic
method (Robertson) This property might influence the dispersal of seeds and seed
form. If the soil surrounding the tree is influenced to benefit the tree and its
growth, then it would make sense that the tree should want its seeds distributed
closely, under the umbrella and in the Ôlitter zoneÕ (Gupta). This experiment
is vital in exploring the relationship of trees seasonal adjustment adaptations and
their relation to affecting overall soil health as it effects the human race
(Mushunksy).

Method:

Part I: Setting Up Testing Sites
1.) We established four sites of contrasting varieties of trees (two conifers and two deciduous i.e. maple, oak, pine, and cedar).
2.) At the designated sites we observed and counted the number of at least 12 inch seedlings under the trees canopies.
3.) We calculated the percent of seedlings by height range under each canopy. We compared total seedlings to that of the total seedlings of the same species to that of the tree.

Part II: Testing Relationship Between Seed Dispersal
4.) In the lab (separately researched) we observed the method of seed dispersal (i.e. size,
structural adaptations, etc.) to determine whether or not the species ÔintendÕ for seedlings to germinate underneath their canopies, or do they travel, by wind or otherwise.

Part III: Conducting pH Tests on Gathered Soil Samples
5.) After we made observations in the undisturbed, designated sites we took a minimum of 28 samplings of 0.5 g of each native soil and of a potting soil control*.
6.) We marked the areas where the samples were taken
7.) In the lab we brought the 0.5g samples into contact with 50 ml of distilled* water for at least 24 hours.
NOTE: We did not disturb samples during this period, so as to not mix sediment into the water.
8.) We tested the water from the soil/water contacts with a pH tester.
9.) We recorded Data in Tables (before section)

Part IV: Setting Up Control Soil Under Designated Tree Sites
10.) Before a substantial amount of new leaf litter has fallen we secured the designated testing sites of native soil.
11.) We secured one baking pan ² full with control potting soil under the canopy per each site for a non buffered comparison.
12.) After the pans/soil is were covered with leaf litter, we set them (undisturbed), and decomposition had begun. We then return to sites approximately three weeks later.
13.) We took another set of samples from each site from both the topsoil (native) and the potting soil (alien microcosm).
14.) In the lab we placed the 0.5g samples in 50ml of the distilled water
15.) We let the samples set for the 24 hour period
16.) We took the pH tests of all samples.
17.) We recorded the data in the second half (after)

NOTE: We compared the native soilÕs pH test results to itself before and after to see if there is any measurable change.
We compared the native soilÕs tests to the potting soilÕs tests of before and after.

Draw Inferences of: possible allelopathic-like qualities, evidence of natural buffer in soil, relationship between seed dispersal and pH results and seedling counts.

*Terms:
Potting soil control- the native soil in Oxford is rich in limestone, therefore is influenced by a natural buffer (acid neutralizer). We purchased the potting soil from our own from a local garden supply store. The potting soil used is different from that of the local soil but the actual pH is 6.5. The potting soil acts as a comparison for this variable especially, but for other unaccountable variables.

Distilled water- distilling the water used to the pH is imperative because water, the universal solvent, is easily contaminated with minerals and nutrients that might influence the results. For an accurate comparison pure water is needed so that the results reflected the differences in the soils, not water quality.

Our Day:
The class would began with a demonstration of a familiar reaction caused by differences in pH, the baking soda/vinegar volcano demo. We then passed out small clay pots with the dessert of Oreo and ice cream. We led the class through a fun exercise on seed distribution. The exercise started out with the class drawing Òa seedÓ on a piece of paper. This explored their pre-conceived notion of what seeds look like. Then we asked them to explain how their seeds are distributed.. After they drew, colored, and wrote their stories about their seed we explained how seed distribution is valid in our experiment and how it pertained to the pH of leaf litter. Overall our day incorporated creative, hands-on interactive activities.

Results:
After collecting the data, we determined if the pH level of the top soil around various types of trees is the result of the falling leaves. Our results showed that indeed this is true. The leaf fall significantly changes the pH of the soil around the tree with the exception of the Silver Maple (Acer saccherinum) whose p-value when calculated is well above 5% allowance. The soil pHÕs after as well as before leaf fall is similar to that of the control soil bringing the result that the sample trees are not allelopathic in any sense.

Conclusion:
Our hypothesis, to determine if there is a significant difference in soil pH in key species of trees before and after the major leaf fall, is indeed inconceivably difficult to prove. The pH levels of our soil samples from the designated species of trees proved to be inconclusive. Without previous knowledge of allelopathic plants it is near impossible to determine if the soil under the tree has been affected by the leaf fall. It may be that there is a natural buffer in the soil around the campus which is composed of limestone that absorbs and nullifies any acidity that is it is exposed to. The fact that the trees have been growing for several decades in the same spot and releasing these leaves yearly may have tempered the soil to the pH level it is currently at. The English Oak, the tree with the greatest chance that its results are not left to chance is secluded by only one adjacent tree, even then the pH levels had minimal change in pH levels. Even then they can be left to the acidity or base of the water that was used in the testing, for it has minuscule changes. Only one of our trees failed to reject the null hypothesis. This tree is surrounded by other trees and was expected to have the greatest difference. Further results to determine if the seed size or growth around the trees are not possible to determine in the given circumstances.
The changes that should be made to this experiment are quite obvious. If we had collected leaves from multiple trees, at least one being from an allelopathic tree, and kept the samples indoors, in potting soil that is not native from the surrounding area we would remove many factors that would change the results. We would have the control as the already discovered allelopath and a basis of comparison for each of our other selected trees. The soil would not affect the test because it is not weathered and balanced by the growth of the trees nor does it have a buffer that would skew the results. If these changes were made it would make it possible to determine if there is a significant difference in soil pH in key species of trees before and after a leaf fall.

Bibliography:
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