plants ‣ Data Nuggets

4.23.15

Growing energy: comparing biofuel crop biomass

The activities are as follows:

Éste Data Nugget también está disponible en Español:

Most of us use fossil fuels every day to power our cars, heat and cool our homes, and make many of the products we buy. Fossil fuels like coal, oil, and natural gas come from plants and animals that lived and died hundreds of millions of years ago – this is why they’re called “fossil” fuels! These ancient energy sources have many uses, but they also have a major problem. When we use them, fossil fuels release carbon dioxide into the atmosphere. As a greenhouse gas, carbon dioxide traps heat and warms the planet. To avoid the serious problems that come with a warmer climate, we need to transition away from fossil fuels and think of new, cleaner ways to power our world.

Biofuels are one of these alternatives. Biofuels are made out of the leaves and stems (called biomass) of plants that are alive and growing today. When harvested, the biomass can be converted into fuel. Plants take in carbon dioxide from the atmosphere to grow. It’s part of the process of photosynthesis. In that way, biofuels can create a balance between the carbon dioxide taken in by plants and what is released when burning fuels.

At the Great Lakes Bioenergy Research Center, scientists and engineers work together to study how to grow plants that take in as much carbon as possible while also producing useful biofuels. Gregg is one of these scientists and he wants to find out how much biomass can be harvested from different plants like corn, grasses, trees, and even weeds. Usually, the bigger and faster a plant grows, the more biomass they make. When more biomass is grown, more biofuels can be produced. Gregg is interested in learning how to produce the most biomass while not harming the environment.

While biofuels may sound like a great solution, Gregg is concerned with how growing them may affect the environment. Biofuels plants come with tradeoffs. Some, like corn, are great at quickly growing to huge heights – but to do this, they often need a lot of fertilizer and pesticides. These can harm the environment, cost farmers money, and may even release more of the greenhouse gasses we are trying to reduce. Other plants might not grow so fast or so big, but also don’t require as many chemicals to grow, and can benefit the environment in other ways, such as by providing habitat for animals. Many of those plants are perennials, meaning that they can grow back year after year without replanting (unlike corn). Common biofuel perennials like switchgrass, Miscanthus grass, prairie grasses, and poplar trees require fewer fertilizers and pesticides to grow, and less fossil fuel-powered equipment to grow and harvest them. Because of this, perennials might be a smart alternative to corn as a source of biofuels.

Gregg out in the WI experimental farm.

Believing in the power of perennials, Gregg thought that it might even be possible to get the same amount of biomass from perennials as is normally harvested from corn, but without using all of the extra chemicals and using less energy. To investigate his ideas, Gregg worked together with a team to design a very big experiment. The team grew many plots of biofuel plants on farms in Wisconsin and Michigan, knowing that the soils at the site in Wisconsin were more nutrient-rich and better for the plants they were studying than at the Michigan site. At each farm, they grew plots of corn, as well as five types of perennial plots: switchgrass, Miscanthus grass, a mix of prairie plant species, young poplar trees, and weeds. For five years, the scientists harvested, dried, and weighed the biomass from each plot every fall. Then, they did the math to find the average amount of biomass produced every year by each plot type at the Wisconsin and Michigan sites.

Featured scientist: Dr. Gregg Sanford from University of Wisconsin-Madison. Written with Marina Kerekes.

Flesch–Kincaid Reading Grade Level = 8.9

This Data Nugget was adapted from a data analysis activity developed by the Great Lakes Bioenergy Research Center (GLBRC). For a more detailed version of this lesson plan, including a supplemental reading, biomass harvest video and extension activities, click here.

This lesson can be paired with The Science of Farming research story to learn a bit more about the process of designing large-scale agricultural experiments that need to account for lots of variables.

For a classroom reading, click here to download an article written for the public on these research findings. Click here for the scientific publication. For more bioenergy lesson plans by the GLBRC, check out their education page.

Aerial view of GLBRC KBS LTER cellulosic biofuels research experiment; Photo Credit: KBS LTER, Michigan State University

For more photos of the GLBRC site in Michigan, click here.

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3.20.15

Springing forward

Scientist Shaun collecting phenology data in the climate change experiment. He is recording the date that the first flowers emerge for dame’s rocket.

Sean Mooney, a high school researcher, collecting phenology data in the climate change experiment. He is recording the date that the first flowers emerge for dame’s rocket.

The Reading Level 1 activities are as follows:

The Reading Level 3 activities are as follows:

Éste Data Nugget también está disponible en Español:

Every day we add more greenhouse gases to our air when we burn fossil fuels like oil, coal, and natural gas. Greenhouse gasses trap the sun’s heat, so as we add more the Earth is heating up! What does climate change mean for the species on our planet? The timing of life cycle events for plants and animals, like flowering and migration, is largely determined by cues organisms take from the environment. The timing of these events is called phenology. Scientists studying phenology are interested in how climate change will influence different species. For example, with warming temperatures and more unpredictable transitions between seasons, what can we expect to happen to the migration timings of birds, mating seasons for animals, or flowering times of plants?

Scientists collecting phenology data in the climate change experiment.

Plants are the foundation for almost all life on Earth. Through photosynthesis, plants produce the oxygen (O₂) that we breathe, food for their own growth and development, food for animals and microbes, and crops that provide food and materials for human society. Because plants are so important to life, we need to find out how climate change could affect them. One good place to start is by looking at flowering plants, guided by the question, how will increased temperatures affect the phenology of flowering? One possible answer to this question is that the date that flowers first emerge for a species is driven by temperature. If this relationship is real, we would expect flowers to emerge earlier each year as temperatures increase due to climate change. But if flowers come out earlier and earlier each year, this could greatly impact plant reproduction and could cause problems for pollinators who count on plants flowering at the same time the pollinators need the pollen for food.

Shaun, Mark, Elizabeth, and Jen are scientists in Michigan who wanted to know if higher temperatures would lead to earlier flowering dates for plants. They chose to look at flowers of dame’s rocket, a leafy plant that is related to the plants we use to make mustard! Mark planted dame’s rocket in eight plots of land. Plots were randomly assigned to one of two treatments. Half of the plots were left to experience normal temperatures (normal), while the other four received a heating treatment to simulate climate change (heated). Air temperatures in heated plots increased by 3°C, which mimics climate change projections for what Michigan will experience by the end of the century. Mark, Elizabeth, and Jen measured the date that each plant produced its first flower, and the survival of each plant. The scientists predicted that dame’s rocket growing in the heated plots would flower earlier than those in the normal plots.

Featured scientists: Shaun Davis from Thornapple Kellogg Middle School and Mark Hammond, Elizabeth Schultheis, and Jen Lau from Michigan State University

Flesch–Kincaid Reading Grade Level = The Reading Level 3 activity has a score of 9.2; the Level 1 has a 6.4.

Flowers of Hesperis matronalis (dame’s rocket), a species of mustard that was introduced to the U.S. from Eurasia.

Additional teacher resources related to this Data Nugget include:

If you would like your students to interact with the raw data, we have attached the original data here. The file also includes weather data over the course of the experiment if students want to ask and explore independent questions.

For a lesson plan that uses citizen science phenology datasets to examine changes in phenology over 30+ year timespans, and address the scientific question, “Do we see evidence for climate change in the phenology of plants and animals?”, click here.
Many phenology datasets are freely available online (many collected by citizen scientists). These datasets are extremely useful because scientists (and your students!) can examine average trends in timing shifts over periods of decades and often in different regions. Phenology datasets available online:
- Lilac flowering phenology dataset
- Ice cover duration for two Michigan lakes
- Nature’s Notebook: A national plant and animal phenology observation program, where students can contribute their phenology data
- ebird: A global bird observation program through Cornell University, students can become citizen scientists and enter data on local bird counts
- hummingbird.net: A place to learn about attracting, watching, feeding, and studying the hummingbirds that breed in North America
NY Times article on research showing what happens when climate change shifts phenology – “5 Plants and Animals Utterly Confused by Climate Change“
Webinar, hosted by Data Nuggets and DataClassroom, exploring the research and data behind this activity.
Webinar exploring how plants respond to climate change, featuring this Data Nugget and LTER scientists!

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4.16.14

Is chocolate for the birds?

Cocoa beans used to make chocolate!

The activities are as follows:

About 9,000 years ago humans invented agriculture as a way to grow enough food for people to eat. Today, agriculture happens all over the globe and takes up 40% of Earth’s land surface. To make space for our food, humans must clear large areas of land, which creates a drastic change, or disturbance, to the habitat. This land-clearing disturbance removes the native plants already there including trees, small flowering plants, and grasses. Many types of animals including mammals, birds, and insects depend on these native plants for food or shelter. Large scale disturbances can make it difficult to live in the area. For example, a woodpecker bird cannot live somewhere that has no trees because they live and find their food in the trees.

However, some agriculture might help some animals because they can use the crops being grown for the food and shelter they need to survive. One example is the cacao tree, which grows in the rainforests of South America. Humans use the seeds of this plant to make chocolate, so it is a very important crop! Cacao trees need very little light. They grow best in a unique habitat called the forest understory, which is composed of the shorter trees and bushes under the large trees found in rainforests. To get a lot of cacao seeds for chocolate, farmers need to have large rainforest trees above their cacao trees for shade. In many ways, cacao farms resemble a native rainforest. Many native plant species grow there and there are still taller tree species. However, these farms are different in important ways from a native rainforest. For example, there are many more short understory trees in the farm than there are in native rainforests. Also, there are fewer small flowering plants on the ground because humans that work on cacao farms trample them as they walk around the farm.

Part I: Skye is a biologist who wanted to know whether rainforest birds use the forest when they are disturbed by adding cacao farms. Skye predicted she would see many fewer birds in the cacao farms, compared to the rainforest. To measure bird abundance, she simply counted birds in each habitat. To do this she chose one rainforest and one cacao farm and set up two transects in each. Transects are parallel lines along which the measurements are taken. She spent four days counting birds along each transect, for a total of eight days in each habitat. She had to get up really early and count birds between 6:00 and 9:00 in the morning because that’s when they are most active.

Part II: Skye was shocked to see so many birds in cacao farms! She decided to take a closer look at her data. Skye wanted to know how the types of birds she saw in the cacao farms compared to the types of birds she saw in the rainforest. She predicted that cacao farms would have different types of birds than the undisturbed rainforest. She thought the bird types would differ because each habitat has different types of food available for birds to eat and different types of plants for birds to live in.

Skye broke her abundance data down to look more closely at four types of birds:

Toucans (Eat: large insects and fruit from large trees, Live: holes in large trees)
Hummingbirds (Eat: nectar from flowers, Live: tree branches and leaves)
Wrens (Eat: small insects, Live: small shrubs on the forest floor)
Flycatchers (Eat: Small insects, Live: tree branches and leaves)

Featured scientist: Skye Greenler from Colorado College and Purdue University

Flesch–Kincaid Reading Grade Level = 8.5

Additional teacher resources related to this Data Nugget:

The research described in this activity has been published. The citation and a PDF of the scientific paper can be found here:
- Greenler, S.M. and J.J. Ebersole (2015) Bird communities in tropical agroforestry ecosystems: an underappreciated conservation resource. Agroforestry Systems 89: 691–704.
The complete dataset for the study has been published to a data repository and is available for classroom use. This dataset has even more data than what is in the Data Nugget activity. While the Data Nugget has data for just two habitats (cacao and rainforest), the full dataset also includes two other agroforest habitat types. The dataset also includes data for every species (169) recorded during the study, whereas the Data Nugget only has data for four families (toucans, wrens, flycatchers, hummingbirds).
Study Location: Skye’s study took place in a 10 km² mixed rainforest, pasture, agro-forest, and monoculture landscape near the village of Pueblo Nuevo de Villa Franca de Guácimo, Limón Province, Costa Rica (10˚20˝ N, 83˚20˝ W), in the Caribbean lowlands 85 km northeast of San José.
For more background on the importance of biodiversity, students can eat this article in The Guardian – What is biodiversity and why does it matter to us?

About Skye: As a child Skye was always asking why; questioning the behavior, characteristics, and interactions of plants and animals around her. She spent her childhood reconstructing deer skeletons to understand how bones and joints functioned and creating endless mini-ecosystems in plastic bottles to watch how they changed over time. This love of discovery, observation, questioning, and experimentation led her to many technician jobs, independent research projects, and graduate research study at Purdue University. At Purdue she studies the factors influencing oak regeneration after ecologically based timber harvest and prescribed fire. While Skye’s primary focus is ecological research, she loves getting to leave the lab and bring science into classrooms to inspire the next generation of young scientists and encourage all students to be always asking why!

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1.10.14

The ground has gas!

Measuring nitrogen (N2O) gas escaping from the soil in summer. Photo credit: Julie Doll, Michigan State University

The activities are as follows:

If you dig through soil, you’ll notice that soil is not hard like a rock, but contains many air pockets between soil grains. These spaces in the soil contain gases, which together are called the soil atmosphere. The soil atmosphere contains the same gases as the atmosphere that surrounds us above ground, but in different concentrations. It has the same amount of nitrogen, slightly less oxygen (O₂), 3-100 times more carbon dioxide (CO₂), and 5-30 times more nitrous oxide (N₂O, which is laughing gas!).

Measuring nitrogen (N2O) gas escaping from the soil in winter. Photo credit: Julie Doll Michigan State University.

Nitrous oxide and carbon dioxide are two greenhouse gasses responsible for much of the warming of global average temperatures. Sometimes soils give off, or emit, these greenhouse gases into the earth’s atmosphere, adding to climate change. Currently scientists are working to figure out why soils emit different amounts of these greenhouse gasses.

During the summer of 2010, Iurii and his fellow researchers at Michigan State University studied nitrous oxide (N₂O) emissions from farm soils. They measured three things: (1) the concentration of nitrous oxide 25 centimeters below the soil’s surface (2) the amount of nitrous oxide leaving the soil (3) and the average temperature on the days that nitrous oxide was measured. The scientists reasoned that the amount of nitrous oxide entering the atmosphere is positively associated with how much nitrous oxide is in the soil and on the soil temperature.

Featured scientist: Iurii Shcherbak from Michigan State University

Flesch–Kincaid Reading Grade Level = 9.2

More information on the research associated with this Data Nugget can be found here.

Data associated with this Data Nugget can be found on the MSU LTER website data tables under GLBRC Biofuel Cropping System Experiment. Bioenergy research classroom materials can be found here. More images can be found on the LTER website.

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1.9.14

Fertilizing biofuels may cause release of greenhouse gasses

An aerial view of the experiment at MSU where biofuels are grown. Photo credit: K. Stepnitz, MSU

The activities are as follows:

Greenhouse gases in our atmosphere, like carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), trap heat from the sun and warm the earth. We need some greenhouse gases to keep the planet warm enough for life. But today, the majority (97%) of scientists agree that the levels of greenhouse gases are getting dangerously high and are causing changes in our climate that may be hard for us to adjust to.

Scientist Leilei collecting samples of gasses released by the growing of biofuels. Photo credit: K. Stepnitz, MSU

When we burn fuels to heat and cool our homes or power our cars we release greenhouse gasses. Most of the energy used today comes from fossil fuels. These energy sources are called “fossil” fuels because they come from plants, algae, and animals that lived hundreds of millions of years ago! After they died, their tissues were buried and slowly turned into coal, oil, and natural gas. An important fact about fossil fuels is that when we use them, they release CO₂ into our atmosphere that was stored millions of years ago. The release of this stored carbon is adding more and more greenhouse gases to our atmosphere, and much faster than today’s plants and algae can remove during photosynthesis. In order to reduce the effects of climate change, we need to change the way we use energy and think of new ways to power our world.

One potential solution could be to grow our fuel instead of drilling for it. Biofuels are a potential substitute for fossil fuels. Biofuels, like fossil fuels, are made from the tissues of plants. The big difference is that they are made from plants that are alive and growing today. Unlike fossil fuels that emit CO₂, biofuel crops first remove CO₂ from the atmosphere as the plants grow and photosynthesize. When biofuels are burned for fuel, the CO₂ is emitted back into the atmosphere, balancing the total amount that was removed and released.

Scientists are interested in figuring out if biofuels make a good replacement for fossil fuels. It is still not clear if the plants that are used to produce biofuels are able to absorb enough CO₂ to offset all of the greenhouse gases that are emitted when biofuels are produced. Additional greenhouse gases are emitted when producing biofuels because it takes energy to plant, water, and harvest the crops, as well as to convert them into fuel. In order to maximize plant growth, many biofuel crops are fertilized by adding nitrogen (N) fertilizer to the soil. However, if there is too much nitrogen in the soil for the crops to take up, it may instead be released into the atmosphere as the gas nitrous oxide (N₂O). N₂O is a greenhouse gas with a global warming potential nearly 300 times higher than CO₂! Global warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere.

Leilei is a scientist who researches whether biofuels make a good alternative to fossil fuels. He wondered what steps farmers could take to reduce the amount of N₂O released when growing biofuel crops. Leilei designed an experiment to determine how much N₂O is emitted when different amounts of nitrogen fertilizer are added to the soil. In other words, he wanted to know whether the amount of N₂O that is emitted into the atmosphere is associated with how much fertilizer is added to the field. To test this idea, he looked at fields of switchgrass, a perennial grass native to North America. Switchgrass is one of the most promising biofuel crops. The fields of switchgrass were first planted in 2008 as a part of a very large long-term study at the Kellogg Biological Station in southwest Michigan. The researchers set up eight fertilization treatments (0, 28, 56, 84, 112, 140, 168, and 196 kg N ha⁻¹) in four replicate fields of switchgrass, for a total of 32 research plots. Leilei measured how much N₂O was released by the soil in the 32 research plots for many years. Here we have two years of Leilei’s data.

Featured scientist: Leilei Ruan from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.1

Additional teacher resources related to this Data Nugget:

Data related to this Data Nugget can be found on the MSU LTER website data tables under GLBRC Biofuel Cropping System Experiment. The data in this activity is the Trace Gas Fluxes from Static Chambers dataset which has N₂O, CO₂, and CH₄ data.
More information on LTER climate change research can be found here.
Bioenergy research classroom materials can be found here.
More images can be found on the LTER website.

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1.9.14

Does a partner in crime make it easier to invade?

The invasive legume plant, hairy vetch, growing in the field.

The activities are as follows:

A mutualism is a relationship between individuals of two different species in which both partners benefit. One example exists between a type of plant, legumes, and a type of bacteria, rhizobia. Rhizobia live inside bumps on the roots of legumes, called nodules. There, they convert nitrogen from the air into a form that can be used by plants; in return, plants provide the rhizobia with food and protection in the root nodule.

Rhizobia nodules on plant roots. In exchange for carbon and protection in the nodules from plants, rhizobia provide fixed nitrogen for plants.

Mutualisms can affect what happens when a plant is moved to a location where that species hasn’t been before. Invasive plants have been transported by humans from one location to another and grow and spread quickly in their new location. For invasive legumes with rhizobia mutualists, there is a chance that the rhizobia will not be moved with it and the plant will have to form new relationships in the new location. These new partners might work well together or might not. Scientists predict that in their new ranges, invasive legumes will grow poorly at first, and then better and better over time. Over generations, invasive plants and their new rhizobia partners may coevolve to become more efficient mutualism partners.

Yi and Tomomi are scientists who tested this hypothesis using one invasive plant species, hairy vetch. They took soil samples from three different spots based on the invasion history: vetch had never been there (no invasion, 0 years), vetch arrived recently (new invasion, less than 3 years), and vetch invaded a long time ago (old invasion, more than 10 years). These soils had rhizobia in them, each with different histories with hairy vetch. Yi and Tomomi took these soils into the greenhouse, divided them into pots, and grew several hairy vetch plants in each soil type. When the plants had grown for some time in the soils, Yi and Tomomi dug them up and measured two things. First, they counted number of nodules on the roots of each plant, which is a way to see how well the mutualism between rhizobia and plants is going. Second, they dried and weighed the plants to measure biomass, which shows how much the plants were growing.

Featured scientists: REU Yi Liu and Tomomi Suwa from Michigan State University

Flesch–Kincaid Reading Grade Level = 8.2

If you are interested in performing your own classroom experiment using the plant-rhizobium mutualism, check out this paper published in the American Biology Teacher describing methods and a proposed experimental design: Suwa and Williamson 2014

1.8.14

Fair traders or freeloaders?

Measuring chlorophyll content in the greenhouse

The activities are as follows:

When two species do better when they cooperate than they would on their own, the relationship is called a mutualism. One example of a mutualism is the relationship between a type of bacteria, rhizobia, and legume plants. Legumes include plants like peas, beans, soybeans, and clover. Rhizobia live in bumps on the legume roots, where they trade their nitrogen for sugar from the plants. Rhizobia fix nitrogen from the air into a form that plants can use. This means that legumes that have rhizobia living in their roots can get more nitrogen than those that don’t.

Under some conditions, this mutualism can break down. For example, if one of the traded resources is very abundant in the environment. When the plant doesn’t need the nitrogen traded by rhizobia, it doesn’t trade as many sugars to the rhizobia. This could cause the rhizobia to evolve to be less cooperative as well. Less-cooperative rhizobia may be found where the soil already has lots of nitrogen. These less-cooperative bacteria are freeloaders: they fix less nitrogen, but still get sugars from the plant and other benefits of living in nodules on their roots.

Rhizobia nodules on plant roots. In exchange for carbon and protection in the nodules from plants, rhizobia provide fixed nitrogen for plants.

One very important legume crop species is the soybean. Soybeans are used to produce vegetable oil, tofu, soymilk, and many other food products. Soybeans trade with rhizobia for nitrogen, but often farmers add more nitrogen into the field as fertilizer. Since farms use a lot of nitrogen fertilizer, researchers at KBS were interested in how different types of farming affected the plant-rhizobia mutualism.

They grew soybean plants in a greenhouse and added rhizobia from three different farms: a high N farm, low N farm, and organic farm that used no N fertilizer. After four weeks, the researchers measured chlorophyll content of the soybean plants. Healthy plants that have lots of nitrogen will have high chlorophyll content, and plants with not enough nitrogen will have low chlorophyll content. Because high nitrogen could lead to the evolution of less-cooperative rhizobia, they expected that rhizobia from organic plots would be most cooperative. They predicted rhizobia from high N plots would be the least cooperative, and rhizobia from low N plots would fall somewhere in the middle. More-cooperative rhizobia provide more nitrogen, so the researchers expected plants grown with cooperative rhizobia to have higher chlorophyll content than plants receiving less-cooperative rhizobia.

Featured scientist: REU Jennifer Schmidt from the Kellogg Biological Station

Flesch–Kincaid Reading Grade Level = 10.1

For more information on the evolution of cheating rhizobia, check out these popular science articles:

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1.7.14

Cheaters in nature – when is a mutualism not a mutualism?

The activities are as follows:

Mutualisms are a special type of relationship in nature where two species work together and both benefit. Each partner trades with the other species, giving a resource and getting one in return. This cooperation leads to partner species doing better when the other is around, and without their partner, each species would have a harder time getting resources.

One important mutualism is between clover, a type of plant, and rhizobia, a type of bacteria. Rhizobia live in small bumps on the clovers’ roots, called nodules, and receive protection and sugar food from the plant. In return, the rhizobia trade nitrogen to the plant, which plants need to photosynthesize and make new DNA. This mutualism works well when soil nitrogen is rare, because it is hard for the plant to collect enough nitrogen on its own, and the plant must rely on rhizobia to get all the nitrogen it needs. But what happens when humans change the game by fertilizing the soil? When nitrogen is no longer rare, will one partner begin to cheat and no longer act as a mutualist?

Worldwide, the nitrogen cycle is off. Not that long ago, before farmers used industrial fertilizers and people burned fossil fuels, nitrogen was rare in the soil. Today, humans are adding large amounts of nitrogen to soils. The nitrogen that we apply to agricultural fields doesn’t stay on those fields, and nitrogen added to the atmosphere when we burn fossil fuels doesn’t stay by the power plant that generates it. The result is that today, more and more plants have all the nitrogen they need. With high nitrogen, plants may no longer depend on rhizobia to help them get nitrogen. This may cause the plant to trade less with the rhizobia in high nitrogen areas. In response, rhizobia from high nitrogen areas may evolve to try harder to get food from the plant, and may even cheat and become parasitic to plants. If this happens, both species will no longer be acting as mutualists.

When Iniyan was a college student, he wanted to study human impacts on the clover-rhizobia mutualism. To find out more, he contacted Jen Lau’s lab at the Kellogg Biological Station one summer, and joined a team of scientists asking these questions. For his own experiment, Iniyan chose two common species of clover: hybrid clover (Trifolium hybridum) and white clover (Trifolium pretense). He chose these two species because they are often planted by farmers. Iniyan then went out and collected rhizobia from farms where nitrogen had been added in large amounts for many years, and other farms where no nitrogen had been added.

Iniyan completed this research as an REU at KBS.

To make sure that there were no rhizobia already in the soil, Iniyan set up his experiment in a field where no clover had grown before. He then planted 45 individuals of each species in the field. He randomly assigned each plant to one of three treatments. For each species, he grew 15 individuals with rhizobia from high nitrogen farms, and 15 with rhizobia from low nitrogen farms. To serve as a control, he grew the remaining 15 individuals without any rhizobia. To add rhizobia to the plants he made two different mixtures. The first was a mix of rhizobia from high nitrogen farms and water, and the second was a mix of rhizobia from low nitrogen farms and water. He then poured one of these mixtures over each of the plants, depending on which rhizobia treatment they were in. The control plants just got water. No nitrogen was added to the plants.

After the plants grew all summer, Iniyan counted the number of leaves and measured the shoot height (cm) for each individual plant. He did not collect biomass because he wanted to let the plants continue to grow. He then averaged the data from each set of 15 individuals. Plants with fewer leaves and shorter shoots are considered less healthy. He predicted rhizobia that evolved in high nitrogen soils would be worse mutualists to plants, while rhizobia that evolved in low nitrogen soils would be good mutualists.

Featured scientist: REU (NSF Research Experience for Undergraduates) Iniyan Ganesan from the Kellogg Biological Station

Flesch–Kincaid Reading Grade Level = 9.5

For more information on the evolution of cheating rhizobia, check out these popular science articles:

1.6.14

Do invasive species escape their enemies?

One of the invasive plants found in the experiment, Dianthus armeria

The activities are as follows:

Invasive species, like zebra mussels and garlic mustard, are species that have been introduced by humans to a new area. Where they invade they cause harm. For example, invasive species outcompete native species and reduce diversity, damage habitats, and interfere with human interests. Damage from invasive species costs the United States over $100 billion per year.

Scientists want to know, what makes an invasive species become such a problem once it is introduced? Is there something that is different for an invasive species compared to native species that have not been moved to a new area? Many things change for an invasive species when it is introduced somewhere new. For example, a plant that is moved across oceans may not bring enemies (like disease, predators, and herbivores) along for the ride. Now that the plant is in a new area with no enemies, it may do very well and become invasive.

Scientists at Michigan State University wanted to test whether invasive species are successful because they have escaped their enemies. They predicted invasive species would get less damage from enemies, compared to native species that still live near to their enemies. If native plants have tons of insects that can eat them, while an invasive plant has few or none, this would support enemy escape explaining invasiveness. However, if researchers find that native and invasive species have the same levels of herbivory, this would no support enemy escape. To test this hypothesis, a lab collected data on invasive and native plant species in Kalamazoo County. They measured how many insects were found on each species of plant, and the percent of leaves that had been damaged by insect herbivores. The data they collected is found below and can be used to test whether invasive plants are successful because they get less damage from insects compared to native plants.

Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 11.3

For a lesson plan on the Enemy Release Hypothesis, click here.
The Denver Museum of Nature and Science has a short video giving background on invasive species, here.

1.6.14

Do insects prefer local or foreign foods?

One of the invasive plants found in the experiment, Centaurea stoebe.

The activities are as follows:

Insects that feed on plants, called herbivores, can have big effects on how plants grow. Herbivory can change the size and shape of plants, the number of flowers and seeds, and even which plant species can survive in a habitat. A plant with leaves eaten by insect herbivores will likely do worse than a plant that is not eaten.

Plants that naturally grow in an area without human interference are called native plants. When a plant is moved by humans to a new area and lives and grows outside of its natural range, it is called an exotic plant. Sometimes exotic plants become invasive, meaning they grow large and fast, take over habitats, and push out native species. What determines if an exotic species will become invasive? Scientists are very interested in this question. Understanding what makes a species become invasive could help control invasions already underway and prevent new ones in the future.

Because herbivory affects how big and fast a plant can grow, local herbivores may determine if an exotic plant thrives in its new habitat and becomes invasive. Elizabeth, a plant biologist, is fascinated by invasive species and wanted to know why they are able to grow bigger and faster than native and other exotic species. One possibility, she thought, is that invasive species are not recognized by the local insect herbivores as good food sources and thus get less damage from the insects. Escaping herbivory could allow invasive species to grow more and may explain how they become invasive.

To test this hypothesis, Elizabeth planted 25 native, 25 exotic, and 11 invasive species in a field in Michigan. This field was already full of many plants and had many insect herbivores. The experimental plants grew from 2011 to 2013. Each year, Elizabeth measured herbivory on 10 individuals of each of the 61 species, for a total of 610 plants. To measure herbivory, she looked at the leaves on each plant and determined how much of each leaf was eaten by herbivores. She then compared the area that was eaten to the total area of the leaf and calculated the proportion leaf area eaten by herbivores. Elizabeth predicted that invasive species would have a lower proportion of leaf area eaten compared to native and noninvasive exotic plants.

Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.9

There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below, as well as a link to access the full dataset from the study:

Schultheis, E.H., A.E. Berardi, and J.A. Lau (2015). No release for the wicked: enemy release is dynamic and not associated with invasiveness. Ecology 96(9) 2446-2457.

Data available from the Dryad Digital Repository

For two lesson plans covering the Enemy Release Hypothesis, click here and here.

Aerial view of the experiments discussed in this activity:

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