Hubbard Brook Analysis: The Effects of Increased Calcium Concentration on Tree Growth

Co-Authored with James F.

Abstract:

In our investigation, we examined the effects of elevated levels of calcium on a forest ecosystem. In the Hubbard Brook Experimental Forest Watershed One, scientists added large amounts of calcium in the form of wollastonite into the first sector, or watershed, of the forest. Our hypothesis was that this calcium, in its ionized form, precipitates out of the forest stream with ions naturally present in the water. We theorized that this precipitation could affect the pH a nearby stream by reacting with acidic or basic ions, such as HSO₄^- or OH^-, thereby pulling the ions out of solution. We also postulated that these extreme levels of calcium would be toxic to plant life, affecting leaf chemistry and potentially having adverse effects on the plants' function, possibly leading to plant death. Additionally, as a result of increased plant death and solids precipitating out of solution, we expected to see increased sediment buildup in a nearby stream. We were unable to investigate this particular hypothesis as adequate data was not recorded after calcium addition. However, we were able to examine the increased biomass of the forest floor, which we believed might correlate with the calcium addition.  For our analysis, we analyzed stream chemistry, leaf chemistry, and forest floor mass of both the control and calcium-enhanced watersheds. We found clear effects in leaf chemical levels of Ca, Mg, Mn, K, and P after calcium addition. Leaf calcium increased, leaf magnesium decreased upon addition, leaf manganese increased to compensate for increased calcium, leaf potassium decreased upon addition, and leaf phosphorous decreased upon addition.  We also noted clear increases in the chemical levels of Ca, PO₄, SiO₂, SO₄, and pH in the stream chemistry after calcium. Finally, we observed a significant increase in forest floor mass that possibly correlated with calcium addition and precipitation.

Introduction:

The purpose of this lab was to examine the effects of calcium on forest ecosystems using data gathered in the Hubbard Brook experiment.  We compared various attributes of forest watershed one before and after the addition of calcium to the system.  We also compared several attributes of forest watershed one, with the addition of calcium, and forest watershed three, the control watershed.  We theorized that calcium cations from the introduction of wollastonite, a calcium compound with the molecular formula CaSiO₃, would precipitate out of the water with other, naturally occurring anions.  We believed that this increased precipitation could result in increased sediment buildup in the river.  Additionally, we believed that the excessive levels of calcium in the environment could be detrimental to the biological function and health of the trees.  We conjectured that the trees would have increased levels of calcium, increased levels of other chemicals involved in calcium processing, and decreased levels of absorption of other necessary chemicals, owing to calcium oversaturation in the soil.  We used several sets of data to study these hypotheses.  We graphed the average thickness of soil and topsoil before and after the calcium addition, we graphed the increased and decreased presences of various substances in the trees’ leaves, and we charted the stream chemistry of the rivers in watershed one and watershed three.  We could not graph the sediment buildup owing to the fact that sediment yield data was not gathered past 1999. 

Results:

The above graph shows the average total thickness of forest floor mass before the addition of calcium to the watershed.  98 plots were surveyed eight times each.  The mean of the overall thicknesses was found to be approximately 8.0, the median thickness was found to be approximately 7.0, and the mode of the set was found to be approximately 5.4. 

The above graph shows the average thickness of the top layer (Oie) of forest floor mass before the addition of calcium to the watershed.  98 plots were surveyed eight times each.  The mean of the overall thickness was found to be approximately 3.7, the median thickness was found to be approximately 3.4, and the mode of the series was found to be approximately 3.6.

The above graph shows the average total thickness of forest floor mass after the addition of calcium to the watershed.  98 plots were surveyed eight times each.  The mean of the overall thicknesses was found to be approximately 8.2, the median thickness was found to be approximately 8.2, and the mode of the set was found to be approximately 4.8.  The mean and the median both show a significant increase form the pre-calcium addition levels, meaning that there was possibly some precipitation of solid from the calcium addition.    

The above graph shows the average thickness of the top layer (Oie) of forest floor mass after the addition of calcium to the watershed.  98 plots were surveyed eight times each.  The mean of the overall thickness was found to be approximately 4.3, the median thickness was found to be approximately 3.9, and the mode of the series was found to be approximately 3.5. The mean and the median both show a significant increase form the pre-calcium addition levels, meaning that there was possibly some precipitation of solid from the calcium addition.   

The above graph shows the effects of increased calcium concentration on leaf biochemistry.  Data was gathered on three different tree species, balsam fir (ABBA), red spruce (PIRU), and white or paper birch (BEPA).  (Hubbard Brook, Watershed 1 Temporal Canopy Leaf Chemistry)  The calcium was added in the year 2000.  (Hubbard Brook, Watershed 1 Temporal Canopy Leaf Chemistry)  After this year, there is a significant increase in the calcium concentration in parts per million, which correlates with our hypothesis. 

The above graph shows the concentration of magnesium in parts per million in leaves as a function of time (before and after the addition of calcium into the system).  As expected, for most tree species the amount of magnesium absorbed upon the addition of calcium decreased.  Two years after the addition of the calcium, the trees with the most significant absorption loss had returned to previous levels of magnesium concentration, perhaps making up for a magnesium deficit. 

The above graph shows the concentration of manganese in parts per million in leaves as a function of time (before and after the addition of calcium into the system).  Manganese is an element that is essential to calcium absorption.  (University of Maryland Medical Center, 2011) The uptake of manganese correlating with an uptake of calcium shows that the leaves have been oversaturated with calcium and need excessive amounts of other ions to process it. 

The above graph shows the concentration of potassium in parts per million in leaves as a function of time (before and after the addition of calcium into the system).  Potassium is an element that is essential to plant growth; along with calcium it is key to the growth of young and developing plants.  (Fromm, 2010)  For ABBA and PIRU species, the initial flood of calcium apparently reduced the plants’ abilities to absorb potassium.  This effect seemed also to be present in BEPA plants, though it should be noted that they made rapid recovery, and soon the potassium levels were much, much higher than in pre-calcium addition plants.

The above graph shows the concentration of phosphorous in parts per million in leaves as a function of time (before and after the addition of calcium into the system).  Phosphorous is an element that is key to sustained plant growth (Baribault, 2012).  For all species, the initial flood of calcium apparently reduced the plants’ abilities to absorb phosphorous.  However, the BEPA species quickly rebounded to levels above the initial pre-calcium levels, possibly to make up for a phosphorous deficit. 

The above graph shows the stream chemistry of watershed three, the control watershed.  This graph shows one large noticeable spike in PO₄ levels, around 400 months. 

The above graph shows the stream chemistry of watershed one, the watershed with calcium added.  This graph also shows one noticeable spike in PO₄ levels around 400 months, however its spike is larger than that of the control.  This could possibly be attributed to the calcium addition and some dissolved precipitate in the stream. 

The above two graphs show the trends of stream chemistry for watersheds three and one, respectively.  The levels of SiO₂ initially increased before leveling out in watershed one, yet in watershed 3 there was no significant trend.  This initial increase could be linked to the presence of calcium.  The levels of Ca were significantly higher in watershed one, as would be expected.  The levels of SO₄ were slightly elevated with calcium, yet both watershed three and watershed one showed a general downward trend over time, indicating that there may be some larger environmental factor affecting the levels.  The pH was elevated with calcium addition, as would be expected (calcium is a naturally basic substance).  

Discussion:

After analyzing the data from the Hubbard Brook watersheds, we found several correlations between calcium addition and changes in leaf chemistry, stream chemistry, and forest floor mass over time.  The above graphs demonstrate the correlation between elevated calcium levels and alterations in plant chemistries.

The first four graphs show an increase in forest floor mass after the addition of calcium.  This increase may be related to elevated levels of calcium leading to toxicity in some plants.  These plants would die and turn into detritus, which would increase the mass of the forest floor. 

            The next five graphs delineate the changes in leaf chemistry of calcium, magnesium, manganese, potassium, and phosphorous.  The addition of calcium in the watershed environment leads to an expected increase of calcium in the leaves themselves.  We not this effect in all of the three plant species studied.  When we analyzed the levels of magnesium, we found a general reduction in the levels of magnesium for all three plant species, noted at the year 2000 for BEPA and ABBA and approximately one year later for PIRU.  This effect is likely the result of excessive calcium saturation of the soil, which could prevent the plants from drawing other ions from the soil.  This would lower the levels of the aforementioned ions in the leaf chemistry analysis.  We subsequently observed the levels of magnesium in the leaves increasing after the initial reduction to higher levels than before.  We may attribute this phenomenon to a deficit in magnesium levels from the blockage, which would cause the plant to overcompensate to restore proper magnesium levels.  The next graph, a plot of manganese levels over time, showed an increase of manganese absorption.  We found in our research that manganese aids in calcium absorption.  Therefore, increased calcium absorption owing to the elevated calcium levels would elicit an increase in manganese absorption to allow for proper calcium processing and integration.  We have noted this general increase in the manganese absorption in all three species of plant studied after the 2000 calcium addition.  All three plant species experienced reduced levels of potassium at the 2000 calcium addition, probably owing to the introduced calcium blocking the absorption of other chemicals.  We note the BEPA plants seemed to make a rapid recovery, unlike ABBA and PIRU, which appear to recover at a slower rate.  This recovery may also be the result of a compensation for a deficiency, similarly to magnesium. Phosphorous absorption is also reduced. This may be attributed to, as noted above, extreme calcium levels blocking the absorption of other chemicals. We also note the extreme recovery of the BEPA plant, perhaps related to compensation for a previous deficiency.

            The last graphs refer to stream chemistry.  PO₄ has its own graph due to the relatively small scale of the concentrations with regards to the other chemicals in question. First, we note the clear increase in calcium levels shown by the graph due to its artificial augmentation by scientists. This calcium addition in watershed one showed a correlation to increases in SiO₂, pH, and SO₄. SiO₂ levels do not show a trend in the control, watershed three, but show a clear increase linked with the calcium addition. Therefore, the calcium addition probably caused, through an unknown set of processes, the increased SiO₂ levels. Similarly, pH was largely stable in watershed 3, but rose in watershed one in a manner tied to the calcium addition. Calcium likely is the cause of this increase, as we hypothesized. SO₄ also increased in this manner, but we note that it trended generally downward during the measurement period. This long-term downward trend is likely due to external factors, perhaps climate change, as the overall trend does not correlate with calcium levels and is present in both watersheds. However, the short-term increase of SO₄ is strongly correlated with and likely caused by calcium addition. Finally, PO₄ generally trended higher at the calcium addition at around month 400. This is increase was likely caused by calcium. Note that there is another relative increase in the PO₄ levels at 300 months. As this deviation is present in both graphs and occurs before addition of calcium, it is likely caused by a larger scale event that would affect both watersheds, such as a climatological incident.

            We do not have any known sources of error because we did not perform the data taking, although, of course, there is some extent to which there is presumable error. If we had the necessary data, we would have examined the sediment buildup as related to increased detritus from calcium toxicity (as indicated by increased forest floor mass).  Another potential project is to find exactly through what means calcium functions to increase PO₄, SiO₂, pH, and SO₄. As hypothesized in the abstract, we believed that a reduction in acidic ions such as HSO₄^- due to their precipitating out of solution by reacting with calcium ions. As for the other compounds, the processes through which they are increased could be chemical reactions or physical, i.e. calcium toxicity causing increased detritus that decomposes into some of the above chemicals.

            Overall, it seems that the introduction of calcium into a forest ecosystem results in possible toxicity to trees, precipitation of natural substances, and significant changes in leaf chemistry.  This phenomenon should be examined further before calcium is implemented in any large-scale projects in forest biomes.

Works Cited:

Baribault, Thomas W., Richard K. Kobe, and Andrew O. Finley. "Tropical Tree Growth Is Correlated with Soil Phosphorous, Potassium, and Calcium, Though Not for Legumes." Ecological Monographs 82.2 (2012): 189-203. ESA Journals. Ecological Society of America, 2012. Web. 9 Apr. 2013. <http://www.esajournals.org/doi/abs/10.1890/11-1013.1>.

Fromm, J. "Wood Formation of Trees in Relation to Potassium and Calcium Nutrition."Tree Physiology 9 (2010): 1140-147. PubMed. US National Library of Medicine, National Institutes of Health, 2 May 2010. Web. 9 Apr. 2013. <http://www.ncbi.nlm.nih.gov/pubmed/20439254>.

Hubbard Brook. "Watershed 1 Temporal Leaf Chemistry." Hubbard Brook Ecosystem Study. LTER Network, n.d. Web. 9 Apr. 2013. <http://hubbardbrook.org/data/dataset.php?id=45>.

University of Maryland Medical Center. "Manganese." University of Maryland Medical Center. A.D.A.M. Inc., 2011. Web. 9 Apr. 2013. <http://www.umm.edu/altmed/articles/manganese-000314.htm>.

Data from the Hubbard Brook Ecosystem Study Data Sets

http://hubbardbrook.org/data/dataset_search.php

Everything You've Ever Wanted to Know About Carbohydrates!

Diagram of a glucose molecule.

You've probably heard quite a bit about carbohydrates.  When dieting you avoid them like the plague; they're in pastas, pizzas, and many other delicious Italian dishes.  But what, in fact, is a carbohydrate?  Carbohydrates are defined as molecules that are some form of sugar (either a polymer or monomer).  These sugars are composed of three elements:  Carbon, Hydrogen, and Oxygen in a 1:2:1 ratio. The carbohydrate most commonly found in nature is Glucose, with the molecular formula C6H12O6 (See right).  Carbohydrates perform several key functions for cells.  They store energy and they provide structure for living organisms.  The simplest sugars, such as Glucose, are referred to as monosaccharides.  Two monosaccharides can be combined to form a molecule called a disaccharide.  The process by which this occurs is called dehydration synthesis.  In dehydration synthesis, one monosaccharide donates a hydroxide ion (OH-) and another donates a hydrogen ion (H+).  These two ions form one molecule of H2O.

The result is that the two monosaccharides are held together in a glycosidic linkage.  Many monosaccharides can be combined in this way to form a polysaccharide.  Polysaccharides are the molecules that we usually think of as "carbohydrates".  They are composed of chains that have hundreds or even thousands of monosaccharides joined together via dehydration.  Interestingly enough, these chains can be broken apart using a process named hydrolysis.  Hydrolysis is, in essence, the opposite of dehydration.  In hydrolysis, the bond between two monosaccharides is broken by introducing a water molecule.  Energy is released, and the glycosidic linkage dissipates.  This is how carbohydrates store energy, by creating large polysaccharides when energy is abundant and breaking up the polysaccharides when energy is scarce.  

There are four common types of carbohydrates found in nature, described below:

1.  Starch

Potatoes, a common starch

Starch is an energy storage polysaccharide found in plants, specifically in their granules. (Want to know more about cell parts?  Click here.)  These molecules are spiral shaped, allowing for more efficient and compact storage.  The presence of starch enables a plant to stockpile its excess glucose and use it later for energy.  Starch can be broken apart by both humans and animals for energy.  Starch is, in fact, composed of two distinct substances.  The first is known as amylose.  Amylose, making up 20% of the molecule's composition, is soluble in water and has a linear shape.  Amylopectin makes up the other 80%.  Amylopectin is branched and, for the most part, not able to be dissolved by water.  Examples of starch include corn, rice, and potatoes.  

2. Glycogen

Glycogen is starch's animal counterpart.  Mostly found in the liver and muscle cells, glycogen is essential to an animal's well-being.  Without glycogen, normal body conditions cannot be maintained for long periods of time.  In fact, human beings must eat some kind of food with carbohydrates, otherwise glycogen stores will be depleted and muscle capabilities will be decreased.

3.  Cellulose

A cross-section of wood.

Cellulose provides structure to plants.  It is a straight, unbranched molecule.  Its components are held together by hydrogen bonds and mibrofibrils.  Cellulose is most commonly found in the cell walls of plants, and is the most commonly found organic compound on the planet.  Interestingly, cellulose is a polymer of glucose, with different glycosidic linkages than that of starch.  Hence, it has a flat shape while starch has a helix shape.  Cellulose is the main component in wood.  Some species of animals, such as termites, have special enzymes that enable them to digest this substance, however humans cannot digest it.

4. Chitin

Chitin is the structural carbohydrate found in many animals.  It is present in the exoskeletons of insects, and the cell walls of funguses.  Chiten has beta linkages with nitrogen attachments, creating its hard, tough surface.  

Sources:

Campbell Biology 9th AP Edition

http://www.medicalnewstoday.com/articles/161547.php

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/carbhyd.htm
http://www.mansfield.ohio-state.edu/~sabedon/068dhsyn.gif
http://homebrewsake.com/wp-content/uploads/2010/04/glucose.gif
http://stemlynsblog.org/wp-content/uploads/2012/07/starch.jpg
http://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Taxus_wood.jpg/300px-Taxus_wood.jpg

Photosynthesis

It's a well known fact that plants need water and sunlight to make food, but how is that possible? Essentially, plants create their own food through a process called photosynthesis. Photosynthesis is made up of two different processes called the light dependent reaction (also called the light reaction) and the light independent reaction (also called the dark reaction or the Calvin cycle). Both of these reactions take place in the chloroplast (shown at the left). The light reactions specifically take place in the thylakoid. Inside each thylakoid there is a system very similar to the electron transport system. This reaction is shown in the image below labeled "Light dependent reaction". This reaction begins with energy from the sun. The plant can use this energy because they have several pigments, one of which is chlorophyll. These pigments allow the plant to absorb the sun's energy. One photon of energy enters into photosystem two (PSII) and bounces off of the walls of photosystem two. The photon then reaches the reaction center at the base of the photosystem. There, a water molecule (H2O) has broken apart into H+ and O2. When the water is broken apart, an electron is released. The photon excites the electron, giving is energy. This electron travels up to the top of photosystem two. It then descends across the system and entersphotosystem one (PSI). As is descends it pumps one H+ ion from the stroma into the thylakoid lumen (the area inside the thylakoid). Once the electron is inside photosystem one, it travels upward until is reaches the electron carrier. There, it reduces NADP+ to NADPH. As this process repeats, a high concentration of H+ ions is build up in the lumen. These ions then travel through the ATP synthase one by one. As they move through, they physically rotate the synthase. This creates energy, and the energy converts ADP and P to ATP. 

As a review, the inputs of the light dependent reaction are as follows:

1 H2O

Light

and the outputs are:

1 O2 (final product)

2 ATP (used in the Calvin Cycle)

1 NADPH (used in the Calvin Cycle)

Light dependent reaction

The next component of photosynthesis is the Calvin Cycle. The calvin cycle creates G3P, or PGAL, which the plant uses to make glucose. It takes three molecules of CO2 to create one molecule of PGAL, therefore this explanation will be describing the cycle in terms of three molecules of CO2. The Calvin Cycle begins with CO2, in this instance three molecules. These molecules of CO2 combine with three molecules of RuBP to form a six carbon molecule. The enzyme rubisco assists in this joining. This is a brief transition phase, and soon these molecules split into three carbon molecules, for a total of six three carbon molecules. These molecules must be rearranged and gain phosphates. Therefore, six ATP oxidize to form ADP and six NADPH oxidize to form six NADP+ and phosphate. Next, the three carbon molecules each lose a carbon. These carbons form a PGAL, and the unused substances are rearranged. The rearranging takes energy, and three ATP oxidize to become 3 ADP. The result is three Rubisco and the cycle continues. When two PGALs are created, they combine to form glucose.

As an overview, the inputs of the Calvin cycle (when one pyruvate is created) are:
3 CO2
9 ATP
6 NADPH

And the outputs are:

9 ADP
6 NADP+
6 P
1 Pyruvate

The equation for photosynthesis is: 6CO2 + 6H2O -> C6H12O6 + 6CO2


This autotrophic system of plants is amazing. Plants take in CO2 and water, two substances that are abundant on our planet, and they convert them to food and oxygen. This phenomenon is present every plant, and even some species of bacteria. It is an essential factor to maintaining the delicate balance of life on Earth. Although we have not yet studied this in class, I believe that the amount of light will assist in photosynthesis and the amount of water. Light would increase the amount of photosynthesis because light is used to excite the electron in the light reaction and water would assist because if there is a lack of water a light reaction cannot occur and therefore there will be no energy to use in the dark reaction.


Sources:

http://en.wikipedia.org/wiki/Photosynthesis

Images:

http://dft.ba/-anQ

http://micro.magnet.fsu.edu/primer/java/photosynthesis/

http://www.daviddarling.info/images/Calvin_cycle.jpg