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

11.4.20

Corals in a strange place

Marine Biologist, Karina, snorkeling in the mangroves. Photo by John Finnerty.

The activities are as follows:

When you imagine a coral, you likely picture it living on a coral reef, bathed in sunlight, surrounded by crystal clear waters teeming with colorful fishes. But corals can actually live in a range of habitats, even habitats that are sometimes murky and much darker!

As marine biologists, Karina and John often snorkel around the mangroves in Belize, where they do their research. Mangroves are trees that have roots able to grow in saltwater. By capturing mud and sediment, these underwater roots build habitat for marine life. While Karina and John were documenting the different marine life that can grow on underwater roots, they noticed something shocking. The same corals that live on coral reefs were growing in the mangrove forests too! This surprised Karina and John because coral reefs and mangrove forests are very different habitats. Coral reefs have clear water and bright light, while mangrove forests are darker with murky water that has a lot of nutrients. How can corals live in such different places?

Karina and John started to wonder if the corals that live in the mangroves look different than the corals on the reefs. Sometimes animals can look different based on where they live. These differences may be adaptations that help them live in different environments. Karina and John measured differences between two different coral species that were found in both habitat types. The two species they used are the mounding mustard hill coral and the branching thin finger coral.   

Featured scientists: Karina Scavo Lord and John Finnerty from Boston University

Flesch–Kincaid Reading Grade Level = 8.9

7.24.20

Limit by limit: Nutrients control algal growth in Arctic streams

The Arctic Stream Team. Frances, Breck, Abby, Alex, Jay, and Arial at Toolik Field Station in 2019. 

The activities are as follows:

You rely on the nutrients from the foods you eat to grow and thrive. Other organisms, like microbes, do as well! Aquatic algae, a type of microbe that live in the water, need to take in nutrients from their surroundings for growth. Two important nutrients for algal growth are nitrogen (N) and phosphorous (P).

Sometimes the environment does not have all the nutrients that aquatic algae need to grow. When one nutrient is less available compared to others, algae can become nutrient limited. Research on nutrient limitation started with Justus Liebig, a 19th century scientist who proposed the “law of the minimum.” The law states that the nutrient available in the lowest amount relative to demand will limit overall growth and production. This means that growth is not controlled by all the nutrients, but by the scarcest one (the “limiting factor”). When more than one nutrient limits growth, algae are considered co-limited. This just means that a combination of two nutrients are needed for algae to grow. Knowing what nutrients are limiting growth helps scientists understand how an ecosystem is working.  

From other research we know that many ecosystems, including those in the Alaskan Arctic, are phosphorus-limited. Scientists figured this out because they found if they added phosphorus, then algae growth increased. However, climate change could change this. As the Arctic warms, ecosystems on land might start to release nutrients in higher amounts or new proportions into the water. These extra nutrients will likely cause increases in algae growth in streams and ponds, which in turn could change food webs and nutrient cycling. It is therefore important to understand which nutrients are currently limiting algae growth before climate change changes things even more. This starts with tests to see how Arctic algae grow in response to changes in N, P, and N and P in the water.  

A team of scientists got to work on this question! Arial, Jay, Frances, Alex, Breck, and Abby are all interested in understanding how climate change may alter nutrient limitations in Arctic streams. Each team member has a unique role in the larger research project. For example, undergraduate researcher Abby spent her 2019 summer at Toolik Field Station in Northern Alaska as part of a research opportunity. She explored nutrient limitation in one particular lake, called Lake I8. 

Abby used small cups that placed into the streams that fed into Lake I8. These cups were filled with agar gel, a material used in labs to grow microbes. Each cup contained different nutrient treatments. Abby used four different treatments in her cups: (1) a control (agar only), (2) agar + nitrogen, (3) agar + phosphorus, and (4) agar + nitrogen + phosphorus. On the top of each cup, she placed a glass disk to provide a surface for the algae to grow.

A. Cups before going into the stream. B. Abby putting out her cup treatments into an Arctic stream. C. Cups incubating under water in an Arctic stream. D. Analyzing Chlorophyll a extracted from the cups. 

Abby put 5 replicate cups for each treatment at both the Inlet and Outlet streams on the I8 Lake. She left them underwater for 4 weeks. She brought the cups back to the lab to measure the algae that grew on each glass disk. Abby measured how much algae grew on each disk by measuring the amount of Chlorophyll a, the green pigment that helps plants photosynthesize. The more pigment, the more the algae is growing. Abby compared the data from the control to each of the other treatments. When there is more growth in a treatment compared to the control, that means a particular nutrient was limiting at that location. Abby expected that the streams would be limited by the amount of phosphorus, but not the amount of nitrogen. She predicted algae would grow more when they are given additional phosphorus compared to the control treatment.

Featured scientists: Abigail Rec from Gettysburg College; Frances Iannucci, Alex Medvedeff, and Breck Bowden from University of Vermont; Arial Shogren and Jay Zarnetske from Michigan State University

Flesch–Kincaid Reading Grade Level = 8.6

4.10.20

Working to reduce the plastics problem

stretching the raw, preformed polymers
Nick (right) and one of his students (left) stretching the raw, preformed polymers.

The activities are as follows:

Plastics are materials that can be shaped easily and are used for many functions. This has made them extremely popular across the world. Thousands of products are made using plastic, including parts of cell phones, food wrappers from your lunch, and even the stitches you may need after an injury. In fact, if you look around right now, you can probably spot at least ten items made of plastic!

Once a plastic is made, it tends to stick around. Synthetic plastics, made by humans from petroleum, cannot be broken down by nature’s decomposers – bacteria and fungi. This means they impact the environment for many, many years. Some types can take thousands of years or longer to break down! 

Nick is a chemist concerned with the negative impacts caused by plastics. He knows that in order to reduce the amount of synthetic plastics in the environment, we need an alternative. And, this alternative needs to be just as good as the synthetic plastic it is replacing. Nick and his undergraduate students at Northland College are testing new ways to make plastics that are biodegradable, meaning they can be decomposed naturally and won’t last as long in the environment. His research focuses on stretchy plastics, called elastomers.Elastomers are what make up rubber bands, tires, hoses, non-latex gloves, and many more items we use every day. 

To try to solve the problem of making a biodegradable elastomer that has all the qualities of a synthetic one, Nick and his students got to work. First, they had to consider the chemical structure of plastics. Plastics are made of polymers. “Poly” means “many” and “mer” means “parts”. This means that plastics are made of long chain molecules with many repeating parts. These repeating parts are called monomers. Different monomers can be used to make different types of plastic.

Nick chose to test two biodegradable monomers – diglycerol and meso-erythritol. Diglycerol is cheap and easy to buy. However, it might be too soft when used on its own. Meso-erythritol is more expensive, but more rigid. They wanted to use diglycerol and meso-erythritol because the chemical structures have the potential to create something that is not too rigid and not too flexible.

Nick and his students designed an experiment in which they tested elastomers made from each of the monomers (diglycerol and meso-erythritol) alone, as well as elastomers made using both types of monomers. They made elastomers with the following percentage ratios of diglycerol over meso-erythritol: 100/0, 75/25, 50/50, 25/75, 0/100. The team was hoping to find the “sweet spot” between a product that is too stiff, and one that is not stiff enough to be useful in elastic materials. Once they finished making their elastomers, they prepared the stretch tests. 

To start a stretch test, the team had to stamp out a piece of material from each elastomer, creating samples with the same size, shape, and thickness. They also cut pieces from rubber bands made of synthetic plastics to compare as a control. Next, they tested the elastomers using a machine that measures how much force is applied (stress) as a material is stretched (strain), both important measures of elasticity. The stress, or force per unit of area, is measured in megapascals (MPa) while the strain, or amount of stretch, is measured as a percent of the original length. 

Featured scientist: Nick Robertson from Northland College. Written by: Theresa Paulsen from Ashland High School, Wisconsin

Flesch–Kincaid Reading Grade Level = 9.6

For additional information on the plastic problem, and Nick’s research, check out the following resources:

« Previous Page
Next Page »