4.20.21

How milkweed plants defend against monarch butterflies

Anurag looking at a monarch caterpillar on a milkweed plant.

The activities are as follows:

For millions of years, monarch butterflies have been antagonizing milkweed plants. Although adult monarchs drink nectar from flowers, their caterpillars only eat milkweed leaves, which harms the plants. This is an ecological interaction called herbivory. The only food for monarchs is milkweed leaves, meaning they have evolved to be highly specialized, picky eaters. But their food is not a passive victim. Like most other plants, milkweeds fight back with defenses against herbivory.

Monarch butterflies lay their eggs on the underside of milkweed leaves. After eggs hatch, caterpillars start to feed and quickly meet the plant’s first defense. Milkweed leaves are covered in thousands of tiny hairs, called trichomes, that the caterpillar needs to shave off before they can take a bite. The next challenge happens when the caterpillar takes a bite of the leaf. They get a mouthful of latex, which is sticky like Elmer’s glue. The caterpillars have to be very careful in how they feed. They cut the veins in the leaf to drain out the latex before continuing to feed on the leaf. Even after monarch caterpillars make it past the trichomes and latex, there’s another defense they need to overcome. Milkweed leaves have chemical toxins called cardiac glycosides, which are poisonous to most animals. As they feed, monarchs eat some of this poison.

Anurag is a scientist who has long been fascinated by plants and their defenses. He thinks this comes from the fact that his mother was such an avid gardener. She would grow food, such as peppers, squashes, and tomatoes. He looks back and has memories that are associated with garden plants and their defenses. For example, he remembers eating a bitter cucumber as a kid and spitting it out. He also can still recall the bitter aroma on his hand after brushing against the sticky tomato leaves. And plants that are tough and stringy, like kale, are not as tasty to eat. These traits are examples of plant defenses in action, making them harder or less enjoyable to eat, reducing herbivory.

Anurag collecting data on milkweed plants.

Anurag first started studying milkweeds 20 years ago, based on a recommendation from a friend. His friend told him of the bitter, sticky, and furry leaves that were treasured by the monarch butterfly caterpillars. This led him to study the paradox of coevolution. The milkweed and monarch have such a tight relationship that over time, milkweeds have evolved multiple ways to defend themselves against their herbivores. In response, monarchs have evolved to overcome those defenses because they need to eat the milkweed. This arms race may continue to shift back and forth over the course of evolutionary time.

This back-and-forth battle between caterpillar and plant intrigued Anurag. He wanted to know whether milkweed’s defensive traits are still effective against monarchs, or have monarchs evolved in ways that make them unaffected by the defenses? Because each defense trait might be at a different phase in the coevolution process, perhaps some would be effective defenses to herbivory, but others would not be effective. He predicted that monarchs would be harmed by all three milkweed defense traits (trichomes, latex, and cardiac glycosides), but that some would cause more harm than others.

To test his ideas, Anurag and his collaborators grew monarch caterpillars on 24 different North American milkweed species. They put a single newly hatched caterpillar on each plant and had five replicate plants per milkweed species. They recorded each caterpillar’s growth over the course of 5 days to see how healthy it was. They also measured the amount of trichomes, latex, and cardiac glycosides in each plant to determine their level of defense. Once they had their data, they looked for a relationship between caterpillar growth and plant defense traits to determine which made the best plant defenses. The better the defense, the less caterpillars would grow.

Featured scientist: Anurag Agrawal (He/Him/His) from Cornell University

Flesch–Kincaid Reading Grade Level = 8.5

Additional teacher resources related to this Data Nugget include:

  • Anurag has other examples, data, and related stories in his book: Monarchs and Milkweed, which is written for budding scientists and interested naturalists: www.amazon.com/dp/0691166358.
  • Students can learn more about Anurag, his research, and his lab at his website: www.herbivory.com which includes blog posts about monarch conservation, the community of insects on milkweed plants, videos of talks and presentations, and other things related to his research and teaching at Cornell University.
  • A scientific article based on this research: Agrawal, A. A., Fishbein, M., Jetter, R., Salminen, J. P., Goldstein, J. B., Freitag, A. E., & Sparks, J. P. (2009). Phylogenetic ecology of leaf surface traits in the milkweeds (Asclepias spp.): chemistry, ecophysiology, and insect behavior. New Phytologist, 183(3), 848-867.
  • Learn more about Anurag and his research in this YouTube video!

3.25.21

Breathing in, Part 2

The activities are as follows:

Susan (left) and Kristina (right), the scientist team leading the ForC project.

In Part 1, you learned how trees “breathe in” and accumulate carbon dioxide within their tissues during photosynthesis. You also examined data from ForC, the Global Forest Carbon Database. Using this dataset, you studied how “breathing in” differed in regrowing forests around the world. Now it’s time to go a step further and see how Susan and Kristina used the ForC database to take action!

Like many other scientists, Susan and Kristina are concerned about global warming. Global warming is the well-documented rise of the temperature of Earth’s surface, oceans, and atmosphere. As of 2020, global temperatures are now warmer by about 1 °C (1.8 °F) than they were before people started burning a lot of fossil fuels in the late 1700’s. While this may seem like a small increase, it has already caused major changes on Earth.

To ease global warming, humanity needs to not only reduce their greenhouse gas emissions, but also to capture the excess greenhouse gases in the atmosphere. This is a huge motivating factor for Kristina and Susan’s investigation into regrowing forests in Part 1 and the main reason they created the ForC database.

Thankfully, Susan and Kristina are not alone. People from all around the world share their concern. That’s one of the reasons the Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the United Nations. The IPCC is dedicated to providing the world with reliable scientific information on the risks, impacts, and response options of climate change. So, it makes sense that the IPCC is also interested in data on carbon accumulation due to forest regrowth.

Susan and Kristina wanted to make sure that the IPCC has the most precise data available in order to better inform policy decisions. They were confident their dataset would improve upon what the IPCC had available when they calculated their estimates. They hoped their work would be incorporated into the IPCC’s next update.

Kristina and Susan thought that the forest carbon accumulation values calculated by ForC would be different than those provided by the IPCC. They anticipated their values would be more precise because of the additional variables they had compiled. In the end, they and their colleagues combined field measurements with 66 environmental variables that could affect carbon accumulation in young regrowing forests. This fine-tuned model was used to create a global map that predicts the potential aboveground carbon accumulation for the first 30 years of forest regrowth. They were able to look at the varying forest types at a finer scale, zooming in to a resolution of one kilometer!

Map showing the distribution of boreal, tropical moist broadleaf, and tropical/subtropical dry broadleaf forests across the globe. Illustrated by Habib Aina.

However, before Susan and Kristina would present their map model to IPCC, they needed to first compare their values with the IPCC’s current model. They chose to focus on three forest types: boreal, tropical dry broadleaf, tropical moist dryleaf. They looked at each forest type on three different continents and compared the estimated values from the IPCC model to the ForC model. If the ForC model is more precise, they expected to see very different values for different locations of the same forest type. If ForC did not increase precision, the values for each continent would be similar to the IPCC values in each forest type.

Featured scientists: Kristina J. Anderson-Teixeira, Smithsonian Conservation Biology Institute & Susan C. Cook-Patton, The Nature Conservancy. Written by Ryan Helcoski.

Flesch–Kincaid Reading Grade Level = 10.0

Additional classroom resources for this Data Nugget:

  • ForC Education: There are lesson plans that can be used to examine the ForC database. This is a private link with additional lesson plans for anyone interested in further exploring the database and asking original questions.
  • If you would like to explore the ForC database in your classroom, students can view the shiny app. Anyone that feels even more ambitious can see the raw data.

3.18.21

Purring crickets: The evolution of a new cricket song

Robin’s team recording purring and typical cricket songs in the field. They analyzed the recordings and discovered that purring was a new song.

The activities are as follows:

Animals use many types of mating signals to attract mates. Some of these signals are probably familiar to you, like the bright colors of birds’ feathers, complex courtship dances of fish, and loud calls of frogs. In crickets, males rub their wings together to produce chirping mating songs that attract females. However, in one species of cricket, these mating songs have led to an issue – while they attract females towards the male, they also attract parasitoid flies. These flies kill the crickets by eating them from the inside out! Parasitoids are animals that lay their eggs in another organism’s body. The eggs develop and usually kill the host.

About twenty years ago, scientists discovered male Pacific field crickets in several spots in Hawaii had stopped making songs. By looking at their wings and DNA, scientists were able to find the exact genetic mutation causing their silence. This change in DNA made some crickets to grow with flat wings that made no sound. Males with this mutation are able to escape detection by the parasitoid flies. However, being silent also posed a struggle because flat winged males could no longer use songs to attract female mates. Scientists waited and watched – would a new way to attract females evolve over time, one that is audible to females, but not to the flies?

Robin is a scientist who has been studying the mating signals in these crickets for many years. One summer, Robin was working in Hawaii and brought a Tupperware container full of crickets into her room. Suddenly, she heard what sounded like a purring cat, but there was no cat in sight. She soon realized the sound was coming from her container of crickets. This song was unlike anything ever observed before in crickets. 

Robin thought that this purring song might be the beginning of the evolution of a novel signal that could be detected by female crickets. If purring is a mating signal, female crickets should have a positive response to purring songs. One way to test this idea is to observe whether females move towards a purring song.

She set out to test her hypothesis with phonotaxis experiments in the lab. During phonotaxis experiments, scientists observe how an organism moves with respect to different sounds. In their first experiment, Robin and her colleagues placed a female at the center of an arena and played a purring song through 1 of 4 speakers. The other 3 speakers were silent. To document the female’s willingness to mate, Robin recorded if the female moved toward the purring and which speakers they contacted. If the purring song was not a mating signal, it should not be attractive to the females and she expected them to contact the speakers at random. This would mean that the purring speaker should be contacted 25% of the time (since only 1 of the 4 speakers broadcast purring). If the purring song was a mating signal, she expected female crickets to contact purring speakers more than 25% of the time.

In a second experiment, Robin investigated whether female crickets prefer purring songs as much as typical mating songs. Using the same set-up, she played either a typical or purring song through 1 of 4 speakers. If females moved toward the speaker playing a  song before the silent ones, she recorded the search time. Search time was calculated as the time it took the female to contact the broadcasting speaker minus the time at which the crickets started looking for the speaker. To see whether the purring song was evolving as a mating signal, she compared the time it took crickets to find speakers broadcasting the purring song compared to the typcal mating song. She predicted that if females still preferred the typical song more than the new song, that they would have longer search times for purring versus typical songs.

Left, a purring male from Moloka’i. Right, a purring male singing to attract mates. Photo credit: E. Dale Broder.

Featured scientist: Robin Tinghitella from The University of Denver.Written by: Gabrielle Welsh

Flesch–Kincaid Reading Grade Level = 9.3

Additional teacher resources related to this Data Nugget include:

2.24.21

Stop that oxidation! What fruit flies teach us about human health

Laboratory fruit flies in their natural habitat: a plastic vial. Photo credit: Conni Wetzker

The activities are as follows:

Have you ever eaten an apple and noticed that, after a while, the core turns brown? That’s because of oxidation – a chemical reaction between the oxygen in the air and the inside of the apple. The same thing is happening inside our own bodies all the time.

Each of our cells is home to mitochondria, tiny factories whose job is to turn the food we eat into the energy we need to live. But mitochondria also make molecules called reactive oxygen species, or ROS. As the name suggests, these molecules contain oxygen and tend to react with the things around them. Like the oxygen in the air reacting with the apple core and turning it brown, ROS react with different parts of the cell, causing oxidative damage. Everything in the cell, including our DNA, can be damaged by ROS molecules. Too much damage contributes to diseases including cancer, heart disease, diabetes, and Parkinson’s.

Bodies can prevent oxidative damage in two ways. First, they can use antioxidants. Antioxidants work by reacting with ROS to stop them from harming cells. Some antioxidants come from the food we eat, while others are made inside the body. If a body doesn’t have enough antioxidants, it can get sick. One example is a genetic mutation called DJ-1. It stops the body from producing antioxidant molecules. Many people with Parkinson’s disease, a neurological illness, have this DJ-1 mutation.

Some living things have evolved a second way to stop oxidative damage: their mitochondria actually make fewer ROS! These species have a special protein called alternative oxidase, or AOX. It works by shortening the pathway that mitochondria use to turn food into energy. A shorter pathway means fewer ROS are made. Scientists have been able to take the AOX gene and move it into other species.

Biz, a scientist studying oxidative damage, wanted to study the effects of the DJ-1 mutation and the AOX gene. To do their research, Biz uses fruit flies. Fruit flies are useful because they are easy to work with and scientists can control the types of mutations and genes they have in the lab. Some of these mutations are the same as those found in humans, so scientists can use them to study human disease. In one study, scientists were able to take the AOX gene and put it into the fruit fly. Fruit flies can also have the DJ-1 mutation that stops antioxidants from being made. Biz used these genetic tools to work with flies that have less oxidative damage (AOX mutants), more oxidative damage (DJ-1 mutants), or normal levels (controls).

Biz was interested in how AOX and DJ-1 affect reproductive cells – sperm and eggs. Oxidative damage is even more dangerous for reproductive cells than for other cells. Whereas most cells can just self-destruct or stop replicating when they build up too much damage, sperm and eggs have to stay healthy up until the moment of fertilization. This wait can last a long time. In many species, females store the male’s sperm inside their own bodies for days, months, or even years after mating! In addition to making their own ROS and antioxidants, sperm and egg cells stored inside the female can be damaged or protected by ROS and antioxidants made by the female’s reproductive tract. Either way, damage to reproductive cells is very important because it can be passed on to future generations or can cause the offspring to die.

Biz wanted to test whether the level of oxidative damage in eggs and stored sperm would influence how many offspring a female had. If cells with oxidative damage do not produce healthy offspring, then fruit flies with less damage should have more offspring.  Biz also expected that fruit flies with more damage should have fewer offspring. To test these ideas, Biz mated normal male fruit flies to three groups of females: females with the AOX gene, females with the DJ-1 mutation, and normal (“control”) females. Aside from having the AOX or DJ-1 gene, the females in all treatments were genetically the same. The males used in the experiment were also genetically identical. After the males and females mated, Biz counted the number of surviving offspring from each group.

Featured scientist: Biz Turnell from Cornell University and Technische Universität Dresden

Flesch–Kincaid Reading Grade Level = 9.0

2.19.21

Getting to the roots of serpentine soils

Alexandria in the field observing the plants and soil.

When an organism grows in different environments, some traits change to fit the conditions. For example, if a houseplant is grown in the shade, it might grow to stretch out long and thin to reach as much light as possible. If that same plant were grown in the sun, it would grow thicker stems and more leaves that are not spread as far apart. This response to the environment helps plants grow in the different conditions they find themselves in.

Flexibility is especially important when a plant is living in a harsh environment. One such environment is serpentine soils. These soils are created from the weathering of the California state rock, Serpentinite. Serpentine soils have high amounts of toxic heavy metals, do not hold water well, and have low nutrient levels. Low levels of water and nutrients found in serpentine soils limit plant growth. In addition, a high level of heavy metals in serpentine soils can actually poison the plant with magnesium!

Combined, these qualities make it so that most types of plants are not able to grow on serpentine soils. However, some plant species have traits that help them tolerate these harsh conditions. Species that are able to live in serpentine soils, but can also grow in other environments, are called serpentine-indifferent.

Alexandria has been working with serpentine soils since 2011 when she was first introduced to them during an undergraduate research experience with her ecology professor. Alexandria was especially intrigued by this challenging environment and how organisms are able to thrive in it, even with the harsh characteristics.

Dot-seed plantain plants in the growth chamber.

To learn more, she started to read articles about previous research on plants that can only grow in serpentine soils. Alexandria learned that these plant species are generally smaller than closely related species. This was interesting, but she still had questions. She noticed the other experiments had compared plant size in different species, not within one species. She thought the next step would be to look at how plants that are the exact same species would respond to serpentine and non-serpentine soil environments. To explore this question, she would need to use serpentine-indifferent plant species because they can grow in serpentine soils and other soils.

Just as a houseplant grows differently in the sun or shade, plants grown in serpentine and non-serpentine soils might change to survive in their environment. Alexandria thought one of these changes could be happening in the roots. She decided to focus on plant roots because of their importance for plant survival and health. Roots are some of the first organs that many plants produce and anchor them to the ground. Throughout a plant’s life, the roots are essential because they bring nutrients to above-ground organs such as leaves. Because serpentine soils have fewer plant nutrients and are drier than non-serpentine soils, Alexandria thought that plants growing in serpentine soils may not invest as much into large root systems. She predicted plants growing in serpentine soils will have smaller roots than plants growing in non-serpentine soils.

To test her ideas, she studied the effects of soil type on a serpentine-indifferent plant species called Dot-seed plantain. She purchased seeds for her experiment from a local commercial seed company. About 5 seeds were planted in serpentine or non-serpentine soils in a growth chamber where growing conditions were kept the same. After the seedlings emerged, the plants were thinned so that there was one plant per pot. The only difference in the environment was the soil type. This allowed Alexandria to attribute any differences in root length to serpentine soils. At the end of her experiment, she pulled the plants out of the soil and measured the root lengths of plants in both treatments.

Featured scientist: Alexandria Igwe (she/her) from University of Miami

Flesch–Kincaid Reading Grade Level = 8.7

Additional resources related to this Data Nugget:

The topics described in this Data Nugget are similar to the published research in the following article:

  • Igwe, A.N. and Vannette, R.L. 2019. Bacterial communities differ between plant species and soil type, and differentially influence seedling establishment on serpentine soils. Plant Soil: 441: 423-437

There is a short video of Alexandria (Allie) sharing her research on serpentine soils.

There have been several news stories and blog posts about this research:

2.4.21

Spiders under the influence

Field picture of an urban web. Dark paper is used to make the web more visible for data collection

The activities are as follows:

People use pharmaceutical drugs, personal care products, and other chemicals on a daily basis. For example, we take medicine when we are sick to feel better, and use perfumes and cologne to make ourselves smell good. After we use these chemicals, where do they go? Often, they get washed down our drains and end up in local waterways. Even our trash can contain these harmful chemicals. For example, when coffee grounds are thrown into the trash, caffeine gets washed into our waterways.

Animals in waterways, like insects, live with these chemicals every day. Many insects are born and grow in the water, absorbing the drugs over their lifetime. As predators eat the insects, the chemicals are passed on, working their way through the food web. For example, spiders living along riverbanks feed off aquatic insects and absorb the drugs from their prey.

Just as chemicals change human behavior, they change spider behavior as well! Effects of drugs on spiders have been studied since the 1940s. Dr. Peter Witt first discovered that chemicals change spider web construction. Peter gave caffeine, and a few other drugs, to spiders to see if they would build their webs during the day instead of at night, which is when they usually work. After giving his test spiders some of the drugs, the spiders still created their webs at night. However, he noticed something unexpected – the web structure of spiders on drugs was completely different from normal webs. The webs were different sizes and had more spacing between each thread. Normal webs help spiders to easily catch prey. Irregularly shaped webs were not good at catching prey because insects could fly right through the large spaces. After his study, Peter knew that drugs were bad for spiders.

Chris (they/them), a current resident of Baltimore and a spider enthusiast, lives in a watershed that is affected by chemical pollution. They wanted to build on Peter’s research by looking at spider webs in the wild instead of in the lab. Chris knew that many types of spiders live near streams and are exposed to toxins through the prey they eat. Chris wanted to compare the effects of the chemicals on spiders in rural and urban environments. By comparing spider webs in these two habitats, they could see how changed the webs are and infer how many chemicals are in the waterways.

Chris worked with Aaron, a local high school teacher, to do this research. They collected images of spiderwebs in areas around Baltimore. They chose two sites: Baisman Run, a rural site far from the city, and Gwynns Run, an urban site close to the city. Chris traveled to the sites and took pictures of eight spiderwebs at each location. Chris and Aaron expected that urban streams would have higher concentrations of chemicals than rural areas because more people live in cities.

When they got back to the lab, Aaron took the pictures and used a computer program to count the number of cells and calculate the total area of each web. These data offer a glimpse into whether spiders near Baltimore are exposed to harmful pharmaceutical chemicals and personal care products. If spiders are exposed to these chemicals, the webs will have fewer, but larger cells than a normal web. The cells will also have irregular shapes.

Featured scientists: Chris Hawn from University of Maryland Baltimore County and Aaron Curry from Baltimore Ecosystem Study LTER

Flesch–Kincaid Reading Grade Level = 7.8

Additional teacher resources related to this Data Nugget include:

  • You can watch Aaron describe his Research Experience for Teachers project here.


1.8.21

Breathing in, Part 1

Susan stands in a reforestation experiment near the Chesapeake Bay.

The activities are as follows:

Photosynthesis is the process by which trees and other plants trap the sun’s energy within the molecular bonds of glucose (C6H12O6), a type of sugar. During photosynthesis, oxygen (O2) is released as a byproduct. For this reason, trees are often portrayed as the lungs of the planet “breathing out” oxygen.

Oxygen is then used by living things for cellular respiration. Your cells use oxygen to free the energy stored within glucose. That is why you, and most living things, need oxygen to survive.

But there’s another aspect of photosynthesis that’s just as important as the release of oxygen. Look at a tree or other plant out your window – how did it get so big? The answer is in the equation for photosynthesis. Carbon dioxide (CO2) and water (H2O) provide the carbon, hydrogen, and oxygen needed to build glucose. Trees use glucose as both an energy source and construction material. As they grow, they arrange glucose in long, winding structures. Some of this carbon becomes part of the plant for as long as they live. This means that the carbon that builds plants comes from the air! This process of pulling carbon out of the atmosphere and holding on to it for long periods of time is known as carbon sequestration or carbon accumulation. It’s what the trees do when they use photosynthesis to “breathe in.”

These processes caught Kristina’s interest. She wanted to know more about how carbon accumulation differed across the globe. So, in 2006, she and a small team of scientists created a database using information from 91 studies on carbon in trees.

In the meantime, Susan was working at the Nature Conservancy and getting tons of questions from people who wanted to plant new forests to help fight climate change. People wanted to know what kinds of forests to plant, and how much carbon they might be able to accumulate. Susan, like Kristina, knew that carbon accumulation differed across the globe and wanted to give people the right numbers for the right places. She started gathering carbon data by sifting through thousands of scientific papers. In the process, she found Kristina’s work. One day, Susan called Kristina to chat.

Kristina and Susan decided they needed to work together to learn more about how carbon accumulation rates differ across various types of forests found around the world. So, they set out to build on previous research and get more accurate measurements. Instead of doing their own new study, they needed to gather data from thousands of existing studies in locations from all over the earth. So that’s exactly what they did. Kristina and Susan, along with an international team of researchers, began their work creating ForC, the Global Forest Carbon Database.

ForC is an open-access database containing over 40,000 records from more than 10,000 plots in over 1,500 geographic areas. All of the data come from published research by scientists and include studies from every forested climate zone. It is a living database that is always being updated as scientists publish their work, making it the most complete source of forest carbon data in the world! It was exactly what Kristina and Susan needed.

Kristina and Susan used ForC to investigate global carbon capture by young regrowing forests. Based on their previous research, they thought that, since tropical forests regrow fastest due to a year-round warm and wet climate, they would have the highest rate of carbon accumulation. In order to study carbon accumulation, they selected 13,112 measurements from young, regrowing (<30 years old) forests around the world. They grouped measurements by forest type, averaged them, and compared their data. With these values, they could inform policy decisions and prioritize forest regrowth in parts of the world that would have the highest impact. Review the table below for information on the six main forest types that Kristina and Susan studied.

Featured scientists: Kristina J. Anderson-Teixeira, Smithsonian Conservation Biology Institute & Susan C. Cook-Patton, The Nature Conservancy. Written by Ryan Helcoski.

Flesch–Kincaid Reading Grade Level = 9.1

Additional classroom resources for this Data Nugget:
If you would like to explore the ForC database in your classroom, students can view the shiny app. Anyone that feels even more ambitious can see the raw data.

Here are two scientific articles related to this activity:

Cook-Patton, SC, Leavitt, SM, Gibbs, D. et al. 2020. Mapping carbon accumulation potential from global natural forest regrowth. Nature 585, 545–550.

Anderson KJ, Allen AP, Gillooly JF, Brown JH. 2006. Temperature-dependence of biomass accumulation rates during secondary succession. Ecology Letters Jun: 9(6):673-82.

1.8.21

To reflect, or not to reflect, that is the question

Jen stops to take a photo while conducting fieldwork in the Arctic.

The activities are as follows:

Since 1978, satellites have measured changes in Arctic sea ice extent, or the area by the North Pole covered by ice. Observations show that Arctic sea ice extent change throughout the year. Arctic sea ice reaches its smallest size at the end of summer in September. Scientists who look at these data over time have noticed the sea ice extent in September has been getting smaller and smaller since 1978. This shocking trend means that the Arctic sea ice is declining, and fast! 

Why does this matter? Well, it turns out that Arctic sea ice plays a major role in the world’s climate system. When energy from the Sun reaches Earth, part of the energy is absorbed by the surface, while the rest is reflected back into space. The energy that is absorbed becomes heat, and warms the planet. The amount of energy reflected back is called albedo.

The higher the albedo, the more energy is reflected off a surface. Complete reflection is assigned a value of 1 (100%) and complete absorption is 0 (0%). Lighter colored surfaces (e.g., white) have a higher albedo than darker colored surfaces (e.g., black). Sea ice is white and reflects about 60% of solar energy striking its surface, so its albedo measurement is 0.60. This means that 40% of the Sun’s energy that reaches the sea ice is absorbed. In contrast, the ocean is much darker and reflects only about 6% of the Sun’s energy striking its surface, so its albedo measurement 0.06. This means that 94% of the Sun’s energy that reaches the ocean is absorbed.

Jen (second from left) preparing to teach her students at the University of Colorado Boulder while working in the Arctic. Photo by Polar Bears International.

Jen first became interested in sea ice in the summer of 2007, when a record low level of sea ice caught scientists off guard. They worried that if the albedo of the Arctic declines, energy that used to be reflected by the white ice will be absorbed by the dark oceans and lead to increased warming. At the time, Jen was working with new satellite observations and found it fascinating to understand what led to the record low sea ice year. To continue her passion, Jen joined a team of scientists studying the Arctic’s energy budget. 

Jen and her team predicted that the decline in the light-colored sea ice will cause Arctic albedo to decrease as well. Jen used incoming and reflected solar energy data to determine the changes in the Arctic’s albedo. These data were collected from satellites as part of the Clouds and Earth’s Radiant Energy System (CERES) project. Then, Jen compared the albedo data to changes in the extent of sea ice from satellite images to look for a pattern. 

Featured scientist: Jen Kay from the Cooperative Institute for Research in Environmental Sciences and the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder. Written by Jon Griffith with support from AGS 1554659 and OPP 1839104.

Flesch–Kincaid Reading Grade Level = 9.6

1.8.21

Fertilizer and fire change microbes in prairie soil

Christine collecting samples from the experimental plots to measure root growth.
Christine collecting samples from the experimental plots to measure root growth.

The activities are as follows:

Stepping out into a prairie feels like looking at a sea of grass, with the horizon evoking a sense of eternity. Grasses and other prairie plants provide important benefits, such as creating habitat for many unique plants, mammals, insects, and microbes. They also help keep our water clean by using nutrients from the soil to grow. When plants take up these nutrients, they prevent them from going into streams. High levels of plant growth also keeps carbon bound up in the bodies of plants instead of in the atmosphere.  

Prairies grow where three environmental conditions come together – a variable climate, frequent fires, and large herbivores roaming the landscape. However, prairies are experiencing many changes. For example, people now work to prevent fires, which allows forest species to establish and eventually take over the prairie. In addition, a lot of land previously covered in prairie is now being used for agriculture. When land is used for agriculture, farmers add nutrients through fertilizer. With all these changes, prairie ecosystems have been declining globally. Scientists are concerned that as they disappear so will the benefits they provide. 

Lydia and Christine are two scientists contributing to the effort to learn more about how to preserve prairies. They both became interested in studying soil because of their appreciation for prairies at a young age. For Lydia, she lived in an area that was covered by trees and farmland, but knew at one time it used to be prairie. This made her want to learn more about prairie environments and how places like where she grew up have changed through history. For Christine, she grew up surrounded by prairies where she developed a passion and curiosity for the natural world. Especially for the organisms living in the soil that you cannot see, called microbes. 

These are two different experimental plots within the large field experiment at Konza Prairie Biological Station. The one with lots of trees is an unburned plot, the one with lots of grass is a burned plot.
These are two different experimental plots within the large field experiment at Konza Prairie Biological Station. The one with lots of trees is an unburned plot, the one with lots of grass is a burned plot.

Lydia and Christine read about how grassland scientists have been doing research to learn more about what happens when fire is stopped and excess nutrients are added. These changes reduce biodiversity and affect which species of plants can grow in the prairie. However, Lydia and Christine noticed that the research had been mostly focused on what happens aboveground.  Lydia and Christine had a hunch that the aboveground communities were not the only things changing. They thought that belowground components would be changed by fire and fertilizer too. They turned their focus to microbes in the soil, because they also use nutrients. In addition, they thought these microorganism would be affected by the changes in aboveground plant biodiversity. 

To see if this was true, they used data that they and other scientists collected at Konza Prairie Biological Station from a large field experiment. The experiment was set up in 1986 and the treatments were applied at the field site every year until 2017! Lydia and Christine focused on the fertilizer (nitrogen) addition and prescribed burning treatments to answer their questions. The nitrogen treatment had eight plots where nitrogen had been added and eight with no nitrogen as a control. Similarly, the prescribed burn treatment was applied to eight plots, while eight plots had no burning as a control. These two treatments were also crossed with each other, meaning that some plots were burned and nitrogen was added.

Lydia and Christine expected the types of microbes in the soil to change in response to the nitrogen and burning treatments because of the different aboveground plant communities and difference in soil nutrients. Soil microbial communities can change in multiple ways. First, the number of unique species can increase or decrease, measured as richness. The other way is how many individuals of each species there are in the community, measured as evenness. Taken together, richness and evenness give a measure of diversity, which can be summarized using the Shannon-Wiener index. The value will get bigger if either richness or evenness increases because it incorporates both. For example, a community with five species that has equal abundance of each will have a larger Shannon-Wiener index than a community with five species where one species has a lot more individuals than the other four.  

Featured Scientists: Lydia Zeglin and Christine Carson from the Konza Prairie Biological Station. Written By: Jaide Allenbrand

Flesch–Kincaid Reading Grade Level = 10.4

12.10.20

Mangroves on the move

mangrove in marsh
A black mangrove growing in the saltmarshes of northern Florida.

The activities are as follows:

All plants need nutrients to grow. Sometimes one nutrient is less abundant than others in a particular environment. This is called a limiting nutrient. If the limiting nutrient is given to the plant, the plant will grow in response. For example, if there is plenty of phosphorus, but very little nitrogen, then adding more phosphorus won’t help plants grow, but adding more nitrogen will. 

Saltmarshes are a common habitat along marine coastlines in North America. Saltmarsh plants get nutrients from both the soil and the seawater that comes in with the tides. In these areas, fertilizers from farms and lawns often end up in the water, adding lots of nutrients that become available to coastal plants. These fertilizers may contain the limiting nutrients that plants need, helping them grow faster and more densely.

One day while Candy, a scientist, was out in a saltmarsh in northern Florida, she noticed something that shouldn’t be there. There was a plant out of place. Normally, saltmarshes in that area are full of grasses and other small plants—there are no trees or woody shrubs. But the plant that Candy noticed was a mangrove. Mangroves are woody plants that can live in saltwater, but are usually only found in tropical places that are very warm. Candy thought the closest mangrove was miles away in the warmer southern parts of Florida. What was this little shrub doing so far from home? The more that Candy and her colleague Emily looked, the more mangroves they found in places they had not been before.

Candy and Emily wondered why mangroves were starting to pop up in northern Florida. Previous research has shown nitrogen and phosphorus are often the limiting nutrients in saltmarshes. They thought that fertilizers being washed into the ocean have made nitrogen or phosphorus available for mangroves, allowing them to grow in that area for the first time. So, Candy and Emily designed an experiment to figure out which nutrient was limiting for saltmarsh plants. 

mangrove saltmarsh researchers
Candy (right) and Emily (left) measure the height of a black mangrove growing in the saltmarsh.

For their study, Candy and Emily chose to focus on black mangroves and saltwort plants. These two species are often found growing together, and mangroves have to compete with saltwort. Candy and Emily found a saltmarsh near St. Augustine, Florida, in which they could set up an experiment. They set up 12 plots that contained both black mangrove and saltwort. Each plot had one mangrove plant and multiple smaller saltwort plants. That way, when they added nutrients to the plots they could compare the responses of mangroves with the responses of saltwort. 

To each of the 12 plots they applied one of three conditions: control (no extra nutrients), nitrogen added, and phosphorus added. They dug two holes in each plot and added the nutrients using fertilizers, which slowly released into the nearby soil. In the case of control plots, they dug the holes but put the soil back without adding fertilizer.

Candy and Emily repeated this process every winter for four years. At the end of four years, they measured plant height and percent cover for the two species. Percent (%) cover is a way of measuring how densely a plant grows, and is the percentage of a given area that a plant takes up when viewed from above. Candy and Emily measured percent cover in 1×1 meter plots. The cover for each species could vary from 0 to 100%.

Featured scientists: Candy Feller from the Smithsonian Environmental Research Center and Emily Dangremond from Roosevelt University

Flesch–Kincaid Reading Grade Level = 8.3

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