Potential REU student projects:

I would be happy to mentor REU students in either of two research areas:

1. Effects of rising carbon dioxide on plant defense against herbivores

2. Nitrogen acquisition by insectivorous plants

 

1.  Effects of rising carbon dioxide on plant defense against herbivores

Rising atmospheric carbon dioxide, primarily from the burning of fossil fuels, is causing plants to have higher levels of carbon but lower levels of nitrogen in their leaves. Today, most plants can defend against herbivores by rapidly increasing their levels of chemical defenses, but this is a nitrogen-intensive response (because it requires rapid synthesis of RNA and enzymes). A student working with me could investigate whether, when grown under the CO2 levels our atmosphere will have at the end of the century, plants 1) have higher pre-attack levels of carbon-based chemical defenses, due to higher carbon content of leaves, but 2) are less able to respond to attack by increasing levels of these same chemical defenses, due to lower nitrogen content of leaves.

An REU student would be able to choose from many plant-defensive chemical-herbivore combinations that could be used to address these questions. For instance, a student could use wild mustard, which contains glucosinolates and is fed upon by the cabbage butterfly (a specialist) and the differential grasshopper (a generalist). Or a student could work with aspen, which contains phenolic glycosides and is fed upon by the gypsy moth and forest tent caterpillar (both generalists) and the aspen tortrix moth (a specialist).

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Caterpillar of the cabbage butterfly feeding on collard, and an example of a glucosinolate, the typical defensive compound of the mustard family.

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Gypsy moth caterpillar feeding on oak, and an example of a phenolic glycoside, the typical defensive compound of aspen trees.

The student would gain experience with High-Pressure Liquid Chromatography (HPLC), the most widely used method for quantifying plant defenses.

hplc chromatogram

An HPLC (left) and chromatogram (right) for quantifying plant defenses.

 

2.  Nitrogen acquisition by insectivorous plants

Insectivory, the eating of insects, is one of the most dramatic adaptations of plants to low-nutrient environments. In Northern Michigan, nitrogen-poor bogs and swales contain two types of plants that have evolved insect-eating leaves: pitcher plants and sundews. In essence, these insectivorous plants have converted at carbon-capture tissue (the leaf) into a nitrogen-capture tissue. While it is a common belief that such plants obtain a substantial portion of their nitrogen from insects, few studies have actually demonstrated this (pitcher plants and sundews also have roots that can absorb nutrients from the slowly decaying plant matter). It is also not entirely clear which plant traits have the largest impact on prey capture rates. Finally, it is also not entirely clear what the ultimate effect is of the species (called inquilines) that live inside the pitcher on nitrogen availability to the plant.

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Insectivorous plants at UMBS, including pitchers with little venation (left) or heavy venation (middle), and a sundew plant(right).

Most nitrogen atoms have 7 protons and 7 neutrons, so are referred to as N14. A small percent of nitrogen atoms have an extra neutron, and comprise the stable isotope N15 (which is a "stable" isotope because it is not radioactive). The ratio of N15 to N14 increases as nitrogen is passed up through the food chain, so the nitrogen in insect prey (which is absorbed through the leaves) has a different ratio than nitrogen from decomposing plant material (which is absorbed through the roots). The N15 to N14 ratio of the pitcher itself therefore indicates how much nitrogen came from insect prey vs. from decomposing plant material. UMBS has a stable isotope mass spectrometer, which an REU student could use to determine, for instance:

1) What traits (such as coloration) make some plants or pitchers better at capturing insects?

2) How flexible is the function of a leaf? For instance, if nitrogen is made more available (by adding directly to a pitcher), will that pitcher turn more green, in order to capture more carbon through photosynthesis?

3. How do the species that live inside pitchers (the inquiline mosquitoes, midges, mites, and rotifers) affect nitrogen capture by the plant? Is the amount of nitrogen they make available to the plant through enhanced prey decomposition more than the amount they steal for their own growth?

4. Are the plant traits that attract inquiline species the same as the ones that attract prey?

 

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