Laboratory #3: Acid Bogs
Note: Dress for the weather and for walking in wet habitats. This means high­topped waterproof boots (we will have some available) or old tennis shoes that you don't mind getting wet. Bring the lab handout, and a notebook and pencil for taking notes. The bog we are visiting is privately owned and is extremely fragile. For example, we will be looking at the Northern Pitcher Plant which is listed on Appendix II of CITES. Please stay with the group and follow the instructions of the instructor and T.A.
Introduction
The purpose of this lab is to introduce you to a bog wetland community, and to consider the physiological adaptations of species to this community type.
Figure 1: Rosette of Sarracenia purpurea (Pitcher Plant)
Acid bogs are the most common type of bog wetland. They tend to have low levels of nutrients. Bogs are classically considered a stage in lake succession but bog­like areas—peatlands—can cover vast areas in the boreal zone. The classical view is that over time, sediments will gradually accumulate and the lake will fill in (see Figure 2). However, recent studies indicate that this may not necessarily be the case for all bogs (VanBreeman, 1995).
The vegetation of classic acid bogs commonly forms a series of concentric rings. In the center and inner rings are the early colonizing species or early successional species. Towards the edges are the late successional species. A transect starting at the center of the open water and moving towards the edge of the bog will ideally go through the following vegetation zones:
1. Open water
2. Floating Plants
3. Sedge mat
4. Ericaceous shrubs

e.g., Leatherleaf, Labrador Tea, Blueberry
5. Conifers

e.g., Tamarack and Black Spruce
Other peatlands may lack the open water, but cover large areas and have the same type of plant communities as found in the mats of the classic bot. Some of the most typical bog plants are Sphagnum, Ericaceous shrubs, carnivorous plants, Black Spruce, and Tamarack. A brief description of each group follows.
Figure 2: Classic model of bog succession
Bog Plants
Sphagnum
Sphagnum more than any other plant shapes bogs and peatlands. It comprises most of the net primary productivity (in peatlands in Northern Minnesota, Chapin et al. (2004) report that Sphagnum and its close relatives contributed 76% of the net annual primary productivity!). Sphagnum dominates the bog communities and is considered a keystone species as its removal from the community would dramatically change the composition and structure of the community.
Sphagnum is a genus of moss. There are between 150­200 species of Sphagnum each of which grows under slightly different environmental conditions (Blackford 2000). In part, Sphagnum plays a keystone role because of two major characteristics. First, Sphagnum has the ability to hold 16­26 times its own dry weight in water. It has specialized dead cells interspersed among the live cells. These dead cells hold large amounts of water. This causes the bog to be wet and raised (Sphagnum expands like a sponge when it absorbs water). Second, Sphagnum has a high cation exchange capacity. This means 2+
that even when nutrients such as Ca are at low concentrations, Spahgnum can absorb them and then +
replace them by returning a H ion to the water. This allows Sphagnum to grow in low nutrient +
solutions but it also causes the water around a Sphagnum plant to have a low pH (i.e., many H ions and therefore, acidic). The lowering of the pH by Sphagnum has been hypothesized as a competitive mechanism, excluding plants that are acid intolerant (see VanBreeman 1995). This acidity slows decay and makes bogs one of the best places to look for data on long­term changes in climate and vegetation (Blackford 2000, Rochefort 2000).
Ericaceous shrubs
Typical ericaceous shrubs are leatherleaf (Chamaedaphne calyculata), blueberry (Vaccinium corymbosum), and Labrador Tea (Ledum groenlandica). Note that many of these plants have evergreen leaves. That is, the leaves of many of these shrubs last for more than one year. Some of them, e.g., leatherleaf, have leaves that turn brown during the winter, and then turn green again the following spring. Keeping leaves may be an adaptation to a low nutrient condition, since new leaves will not have to be manufactured annually. In addition, some plants can take advantage of year­round photosynthesis (if conditions are favorable).
Tamarack (Larch) and Black Spruce
Tamarack (Larix laricina) and Black Spruce (Picea mariana) are two common bog trees. These trees are both conifers. Tamarack is unusual in that it is a deciduous conifer ­ it loses its needles in the fall and grows new ones in the spring. Oftentimes these trees have mycorrhizal associations which are mutualisms between the root of the plant and a fungus. This can enhance nutrient uptake, particularly that of potassium. Carnivorous plants
Typical carnivorous plants such as pitcher plants (Sarracinea), sundews (Drosera) and bladderworts (Utricularia) have modified leaves which capture insects. These plants are photosynthetic and acquire energy from sunlight. They use the insects as a source of nitrogen and other mineral nutrients. Sundews capture insects on sticky secretions from leaf hairs. Pitcher plants use a different method. The leaves of pitcher plants form a container that fills with water. Insects fall into the water and are unable to crawl out because of downward­pointing hairs that line the inside of the leaf. The plant secretes enzymes into the water and digests the drowned insects. Bog Animals
Pitcher­plant mosquito
Several organisms have evolved resistance to the pitcher plant digestive enzymes and have larvae that live in the plant's modified leaves. One prominent example is the pitcher plant mosquito Wyeomyia. The larvae of this particular species are found nowhere else. Look into the pitcher plants on the bog and see if you can spot tiny, wriggling mosquito larvae.
“The Bog Ant”
Bog ant communities are composed of a set of species that is distinct from surrounding forest ant communities (Ellison et al., 2002). Of particular interest is the “Bog Ant”, Myrmica lobifrons, which is a specialist of bog communities. Myrmica lobifrons has only recently been recorded in Massachusetts – Personally, I'm looking forward to finding this species, for the first time, on this field trip!
References
Blackford, J. 2000. Palaeoclimatic records from peat bogs. Trends in Ecology and Evolution. 15: 193­
198.
Chapin, C.T. S.D. Bridgham and J. Pastor. 2004. pH and nutrient effects on aboveground net primary production in a Minnesota, USA bog and fen. Wetlands 24: 186­201.
Ellison, A.M., Farnsworth, E.J., Gotelli, N.J. 2002. Ant diversity in pitcher­plant bogs of Massachusetts. Northeastern Naturalist 9: 267–284.
Johnson, L.C. and A.W.H. Damman. 1991. Species­controlled Sphagnum decay on a South Swedish raised bog. Oikos 61:234­242.
Rochefort, L. 2000. Sphagnum—a keystone genus in habitat restoration. The Bryologist 103: 503­508.
VanBreemen, N. 1995. How Sphagnum bogs down other plants. Trends in Ecology and Evolution. 10: 270­275.