9.15.23

A difficult drought

A field of switchgrass studied by biofuels researchers.

The activities are as follows:

Most people use fossil fuels like natural gas, coal, and oil daily. We use them to generate much of the energy that gets us from place to place, power our homes, and more. Fossil fuels are very efficient at producing energy, but they also come with negative consequences. For example, when burned, they release greenhouse gases like carbon dioxide into our atmosphere. The right balance of greenhouse gasses is needed to keep our planet warm enough to live on. However, because we have burned so many fossil fuels, the earth has gotten too hot too fast, resulting in climate change. Scientists are looking for other ways to fuel our lives with less damage to our environment.

Substituting fossil fuels with biofuels is one of these options. Biofuels are fuels made from plants. Unlike fossil fuels, which take millions of years to form, biofuels are renewable. They are made from plants grown and harvested every few years. Using biofuels instead of fossil fuels can be better for our environment because they do not release ancient carbon like burning fossil fuels does. In addition, the plants made into biofuels take in carbon dioxide from the atmosphere as they grow.

To become biofuels, plants need to go through a series of chemical and physical processes. The sugar stored in plant cells must undergo fermentation. In this process, microorganisms, like yeast, transform the sugars into ethanol that can be used for fuels. Trey is a scientist at the Great Lakes Bioenergy Center. He is interested in seeing how yeast’s ability to transform sugar into fuel is affected by environmental conditions in fields, such as temperature and rainfall.

When there was a major drought in 2012, Trey used the opportunity to study the impacts of drought. The growing season had very high temperatures and very low rainfall. These conditions make it more difficult for plants to grow, including switchgrass, a prairie grass being studied as a potential biofuel source.

Trey knew that drought affects the amount and quality of switchgrass that can be harvested. He wanted to find out if drought also had effects on the ability of yeast to transform the plants’ sugars into ethanol. Stress from droughts is known to cause a build-up of compounds in plant cells that help them survive during drought. Trey thought that these extra compounds might harm the yeast or make it difficult for the yeast to break down the sugars during the fermentation process. Trey and his team predicted that if they fed yeast a sample of switchgrass grown during the 2012 drought, the yeast would struggle to ferment its sugars and produce fewer biofuels as a result.  

To test their idea, the team studied two different sets of switchgrass samples that were grown and collected in Wisconsin. One set of switchgrass was grown in 2010 under normal conditions. The other set was grown during the 2012 drought. The team introduced the two samples to yeast in a controlled setting and performed four fermentation tests for each set of switchgrass. They recorded the amount of ethanol produced during each test.

Featured scientists: Trey Sato from the University of Wisconsin-Madison. Written by Marina Kerekes.

Flesch–Kincaid Reading Grade Level = 8.2

Additional teacher resources related to this Data Nugget include:

There are other Data Nuggets that share biofuels research. Search this table for “GLBRC” to find more! Some of the popular activities include:

The Great Lakes Bioenergy Research Center (GLBRC) has many biofuel-related resources available to K16 educators on their webpage.

For activities related specifically to this Data Nugget, see:

6.1.23

Collaborative cropping: Can plants help each other grow?

The activities are as follows:

Alfalfa (middle) planted in a Kernza® field.

Most of the crops grown on farms in the United States are annual plants, like corn, soybeans, and wheat. Annual plants die every year after harvest and must be replanted the following year. Preparing farm fields for replanting every year can erode soils and hurt important bacteria and fungi living in the soil.

One way to change how we produce food is to grow more perennial crops. Perennial plants live for many years and don’t need to be replanted. Perennials stay in the ground all year and start growing right away in the spring before annual crops are even planted. This early growth also gives perennial crops a “head-start” in competing with annual weed species that emerge later in the season.

While there are potential benefits of perennial crops, they are not commonly planted because they tend to make lower profits for farmers than annual crops. Crop scientists are still examining potential options to make perennial crops work at a large scale for farmers. For twenty years, researchers at The Land Institute in Kansas and at the University of Minnesota have been looking at a new perennial grain, called Kernza®, that could be used as an alternative to wheat and rye annual crops. Kernza® comes from the seeds of a plant called intermediate wheatgrass. Because Kernza® is such a new crop, scientists still have a lot to learn about it. Before it can be widely used by farmers, they want to know what field conditions help the plants grow to ensure the crop makes money for farmers.

Dr. Jake Jungers taking a soil core in a Kernza® field.

One strategy to improve field conditions for perennial crops is to plant legumes in the field alongside them. Legumes can make nitrogen, a nutrient that plants need to grow, more available to the plants around them. Additionally, farmers can select legume species that typically don’t compete with the crop but may outcompete weeds.

Jake is an ecologist who uses his knowledge about plants to make agriculture more sustainable. Jake wanted to do some research into alfalfa, a type of perennial legume that might work well with Kernza®. Jake thought that growing alfalfa alongside Kernza® would lead to increased profit and yield for two reasons. One, because it would add nitrogen to the soil to boost crop growth. Two, because alfalfa would compete with agricultural weed species, making valuable resources available for the crop plants.

To test this idea, Jake set up an experiment with his team. Alfalfa was grown with Kernza® at three different locations in Minnesota in 2019. The study was replicated four times at each site, with the same amount of alfalfa and Kernza® planted into each field. At the end of the growing season, the fields were harvested, and the plants were sorted into three categories: Kernza®, alfalfa, and weed species. He further sorted Kernza® by grain, which can be used for food, and straw, which can be used for animal feed. Jake wanted to compare yield, or plant growth per unit area, across the plant categories. To do this, he weighed all the plants in each category to get the biomass and then divided by the area of the field.

Featured scientist: Jake Jungers (he/him) from the University of Minnesota

Written by Claire Wineman (she/her)

Flesch–Kincaid Reading Grade Level = 8.5

8.20.22

Nitrate: Good for plants, bad for drinking water

Evelyn is a scientist at the University of Minnesota. She studies nitrate pollution and how growing perennial crops may prevent it from entering our drinking water.

The activities are as follows:

Nitrogen is the most abundant element in our atmosphere. All living things need nitrogen to live and grow, but plants and animals can’t use the atmospheric form. Instead, many plants extract nitrogen from the soil and in the case of crops, we supply nitrogen through fertilizer, in a form called nitrate.

Nitrate dissolves well in water. This helps make it easy for plants to use, but it can also end up in rivers and groundwater. Groundwater with just 10 milligrams of nitrate per liter is not safe to drink because it can lead to a higher risk of cancer and birth defects. It is really expensive to remove nitrate from drinking water. Towns whose groundwater is contaminated must either pay to remove it or find a new drinking water source. Virtually all nitrate pollution comes from fertilizers used on crops, so one way to address this problem is to change the way we farm.

Annual plants live for just one season and typically have smaller shallower root systems than perennial plants, which live for multiple seasons. Most farmland grows annuals like corn and soybeans, but we get some of our food from perennials like apples, hazelnuts, and raspberries. Perennials stay in the ground all year and start growing right away in the spring before annual crops are even planted. Perennial grasses are particularly good at growing deep roots and taking up lots of nitrate from the soil. If we could produce more food from perennial plants instead of annual plants, crops may absorb enough nitrate to prevent it from getting into our drinking water.

For twenty years, researchers at The Land Institute in Kansas and at the University of Minnesota have been working on a new perennial grain crop called Kernza®, the seeds from a plant called intermediate wheatgrass. Kernza® can be used like wheat or rye, but it has a larger, deeper root system than regular annual wheat. Perennial plants’ deep roots are really good at absorbing dissolved nitrate in soil, so scientists wanted to study Kernza® in the field to see if it would prevent nitrate getting into groundwater.

Evelyn is one of these researchers. She grew up in Minneapolis, Minnesota and as a high school student, she was surprised to learn that agriculture has a huge impact on soil and water quality, wildlife habitat, and biodiversity. She wanted to help protect the environment, so she studied Food Systems at the University of Minnesota. A few years later, she joined a project that involved planting Kernza® in rural areas to prevent and reduce nitrate contamination of drinking water. Farmers, city officials, water managers, and scientists worked together to find solutions. This project inspired Evelyn to study Kernza® and nitrate for her master’s degree.

In her experiment, Evelyn planted plots of Kernza® (foreground) and plots with a corn-soybean rotation (background). This photo was taken in a corn year. Lysimeters are used to collect groundwater samples. The white posts are holding up the lysimeter sampling tubes.

To see if Kernza® helped absorb more nitrate from soil than annual crops, Evelyn and her colleagues ran an experiment. They planted plots of Kernza® and other plots that rotated between corn and soybean every year. Plots with Kernza® and corn were fertilized with nitrogen. Soybean plots were not fertilized.

In the plots, they installed lysimeters: long tubes that go down several feet to collect soil water from below where most plant roots can reach it. Soil water is the water that sits between soil particles. It can be taken up by plant roots or trickle down into the groundwater that is used for drinking wells. Once it moves deeper than a plant’s roots, it can’t be taken up and is very likely to reach the groundwater. Evelyn took water samples from the lysimeters every ten days and analyzed them for nitrate concentration.  If more nitrate is found in soil water under corn and soybean plots than Kernza®, this would be good evidence that Kernza® takes up more nitrate and helps protect groundwater.

Featured scientist: Evelyn Reilly (she/her) from University of Minnesota

Flesch–Kincaid Reading Grade Level = 10.9

6.7.21

Blinking out?

A researcher collects data from a yellow sticky card at the MSU KBS LTER site. Photo Credit: K. Stepnitz, Michigan State University.

The activities are as follows:

The longest surveys of fireflies known to science was actually started by accident!

At the Kellogg Biological Station Long-Term Ecological Research Site, scientists work together to answer questions that can only be studied with long-term data. Their focus is to collect data in the same way over many consecutive years to look for patterns through time. One of these long-term studies, looking at lady beetle populations, was developed to keep watch on these important species. To count lady beetles, scientists placed yellow sticky card traps out in the same plots year after year. These data are used to figure out if lady beetle numbers are changing over time.

Because sticky traps catch everything small that flies by, other insect species get stuck as well. One day, a research technician noticed this and decided to add a few new columns to the data sheet. That way they could start recording data on the other insect species found on the sticky traps. Each year the technician kept adding to the record and over time, more and more data were collected. One of those new columns happened to record the number of fireflies caught. Though the exact reason for this data collection is lost to history, scientists quickly realized the value of this dataset! 

Several years later, Julia became the lab technician. She took over the responsibility of the sticky trap count, adding to the dataset. Christie joined this same lab as a scientist and stumbled upon the data on fireflies that Julia and the previous technician had collected. She wanted to take advantage of the long-term data and analyze whether firefly populations had been increasing or decreasing. 

Many people have fond memories of watching fireflies blink across open fields and collecting them in jars as children. This is one of the reasons why fireflies are a beloved insect species. Julia grew up in southwest Michigan and fondly recalls spending summers watching them blink over yards and open fields, catching them in jars to watch them for a little while. Christie did the same in her parent’s yard in rural Ontario! That fondness never really went away and both enjoy watching the fireflies around Northeast Ohio where they currently live. Fireflies are also an important part of the ecosystems where they live. Larvae spend most of their time in the soil and are predators of insects and other small animals, such as snails. 

All the insects collected on a yellow sticky card trap over the course of one week. Photo credit: Elizabeth D’Auria, Michigan State University.

Many scientists and citizens alike have noticed that they aren’t seeing as many fireflies as they used to. Habitat loss and light pollution could be causing problems for fireflies. This is where the importance of long-term data really comes into play. Long-term data are critical to identifying and understanding natural population cycles over long periods of time that we wouldn’t be able to see with just a few years of data. It also gives scientists opportunities to answer unanticipated research questions. In this situation, even though the data were collected without a specific purpose in mind, having the dataset available offered new opportunities! Christie and Julia were able to look at the long-term changes in southwest Michigan firefly populations, something they would not have been able to do before the research technician added those extra columns. In order to start answering this question, they compiled all of the years of firefly data and began to compare the average counts from year to year. Although data were collected in multiple different habitat types, they focused on data from open fields because fireflies use these areas to find mates.

Featured scientists: Christie Bahlai and Julia Perrone from Kent State University. Data from the Kellogg Biological Station LTER.

Flesch–Kincaid Reading Grade Level = 10.7

Additional teacher resources related to this Data Nugget include:

1.25.19

Fast weeds in farmer’s fields

Native and weedy radish plants.

The activities are as follows:

Weeds in agricultural fields cost farmers $28 billion per year in just the United States alone. When fields are full of weeds the crops do not grow as well. Sometimes weeds even grow better than the crops in the same field. This may make you wonder, how do weeds grow so well compared to other types of plants? Scientists think that weeds may have evolved certain traits that allow them do well in agricultural fields. These adaptations could allow them to grow better and pass on more of their genes to the next generation.

Weedy radish is considered one of the world’s worst agricultural weeds. This plant has spread around the world and can now be found on every continent except Antarctica. Weedy radish commonly invades wheat and oat fields. It grows better than crops and lowers the amount of food produced in these fields. Weedy radish evolved from native radish only after humans started growing crops. Native radish only grows in natural habitats in the Mediterranean region. 

Because weedy radish evolved from native radish recently, they are still very closely related. They are so closely related they are actually listed as the same species. However, some traits have evolved rapidly in weedy radish. For example, native radish grow much slower and take a few months to make flowers. However, weedy radish can make flowers only three weeks after sprouting! In a farmer’s field, the crop might be harvested before a native radish would be able to make any seeds, while weedy radish had plenty of time to make seeds.

Ashley collecting data on the traits of weedy and native radish. 

The differences between native versus weedy radish interested Ashley, a teacher in Michigan. To learn more she sought out a scientist studying this species. She found Jeff, a plant biologist at the Kellogg Biological Station and she joined his lab for a summer to work with him. That summer, Ashley ran an experiment where she tested whether the rapid flowering and seed production of weedy radish was an adaptation to life in agricultural fields.

Ashley planted four populations of native radish and three populations of weedy radish into fields growing oat crops. Ashley made sure to plant multiple populations of radish to add replication to her experiment. Multiple populations allowed her to see if patterns were the same across populations or if each population grew differently. For each of these populations she measured flowering frequency. This trait is the total number of plants that produced flowers within the limited time between tilling and harvesting. Ashley also measured fitness, by counting the total number of seeds each plant produced over its lifetime. Whichever plant type produced a greater number of seeds had higher fitness. Oats only grow for 12 weeks so if radish plants were going to flower and make seeds they would have to do it fast. Ashley predicted the weedy radish population would produce more flowers and seeds than native radish during the study. Ashley expected few native radish plants would flower before harvest.

Featured scientists: Ashley Carroll from Gull Lake Middle School and Jeff Conner from the Kellogg Biological Station at Michigan State University

Flesch–Kincaid Reading Grade Level = 9.1

11.12.18

Can biochar improve crop yields?

Buckets of pine wood biochar.

The activities are as follows:

If you walk through the lush Amazon rainforest, the huge trees may be the first thing you see. But, did you know there are wonderful things to explore on the forest floor? In special places of the Amazon, there exist incredible dark soils called “Terra Preta”. These soils are rich in nutrients that help plants grow. The main source of nutrients and dark color is from charcoal added by humans. Hundreds of years ago the indigenous people added their cooking waste, including ash from fire pits, into the ground to help their food crops grow. Today, scientists and farmers are trying out this same ancient method. When this charcoal is added to soil to help plants grow, we call it biochar.

Biochar is a pretty unique material. It is created by a special process that is similar to burning materials in a fire place, but without oxygen. Biochar can be made from many different materials. Most biochar has lots of tiny spaces, or pores, that cause it to act like a hard sponge when it is in the soil. Due to these pores, the biochar can hold more water than the soil can by itself. Along with that extra water, it also can hold nutrients. Biochar has been shown to increase crop yield in tropical places like the Amazon.

Farmers in western Colorado wanted to know what would happen if they added biochar to fields near them. Their farms experience a very different climate that is cooler and drier than the Amazon. In these drier environments, farmers are concerned about the amount of water in the soil, especially during droughts. Farmers had so many questions about how biochar works in soils that scientists at Colorado State University decided to help. One scientist, Erika, was curious if biochar could really help farms in dry Colorado. Erika thought that biochar could increase crop yield by providing pores that would hold more water in the soil that crop plants can use to grow.

Matt, a soil scientist, applying biochar to the field in a treatment plot.

To test the effects of biochar in dry agricultural environments, Erika set up an experiment at the Colorado State University Agricultural Research and Development Center. She set up plots with three different soil conditions: biochar added, manure added, and a control. She chose to include a manure treatment because it is what farmers in Colorado were currently adding to their soil when they farmed. For each treatment she had 4 replicate plots, for a total of 12 plots. She added biochar or manure to a field at the same rate (30 Megagrams/ ha or 13 tons/acre). She didn’t add anything to control plots. Erika then planted corn seeds into all 12 plots.

Erika also wanted to know if the effects of biochar would be different when water was limited compared to when it was plentiful. She set up another experimental treatment with two different irrigation levels: fullirrigationandlimitedirrigation. The full irrigation plots were watered whenever the plants needed it. The limited irrigation plots were not watered for the whole month of July, giving crops a drought period during the growing season. Erika predicted that the plots with biochar would have more water in the soil. She also thought that corn yields would be higher with biochar than in the manure and control plots. She predicted these patterns would be true under both the full and limited irrigation treatments. However, she thought that the biochar would be most beneficial when crops were given less water in the limited irrigation treatments.

To measure the water in the soil, Erika took soil samples three times: a few weeks after planting (June), the middle of the growing season (July), and just before corn harvest (September). She weighedout 10 gofmoistsoil, thendried the samples for24 hoursin an oven and weighed them again. By putting the soil in the oven, the water evaporates out and leaves just the dry soil. Sarah divided the weight of the water lost by the weight of the dry soil to calculate the percent soil moisture. At the end of the season she measured crop yield as the dry weight of the corn cobs in bushes per acre (bu/acre).

Featured scientist: Erika Foster from Colorado State University

Flesch–Kincaid Reading Grade Level = 8.9

Resources to pair with this Data Nugget:

4.23.15

Growing energy: comparing biofuel crop biomass

The activities are as follows:GLBRC1

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.

GLBRC2

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 GLBRC

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

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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4.16.14

Is chocolate for the birds?

Cocoa beans used to make chocolate!

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.

rainforest and cacao plantation

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:

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

skyecacao

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:
  • 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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1.8.14

Fair traders or freeloaders?

Measuring chlorophyll content in the greenhouse

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.

Photo by Tomomi Suwa, 2013

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:

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

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