Even though southern Minnesota is hitting peak leaf color right now, University of Minnesota tree lovers were talking about the transition from summer to fall at the Midtown Farmer’s Market on October 1st. Just like us, trees need to prepare for the winter. Unlike the tomato plants in your garden, which die off and can be replanted from seed in the spring, or prairie grasses, which go dormant at or beneath the surface of the soil, trees have have to survive winter with their entire bodies in the freezing air. Some of them even keep their leaves all winter – and supporting all of that living tissue in a cold environment can be a big challenge!
One of the most obvious ways that many trees prepare for winter is by shedding their leaves. During the spring and summer, green leaves, filled with nutrient-rich chlorophyll, make food through photosynthesis. As the days get shorter and colder, trees will suck up as much of the chlorophyll in their leaves as they can. This is a way of recycling nutrients, which can be used next year. The leaves are left without much green pigment, but with plenty of the anthocyanins and carotenoids that produce red, orange, and yellow colors. This is why leaves change color in the fall. The reds and yellows we see in October aren’t new pigments – they were there all along, hiding behind the green. After trees have taken as much out of their leaves, they let them “senesce,” or die off in a controlled way. This is different, and less damaging for the tree, than the freezing damage that you will observe if you leave your houseplants outside during a hard frost.
Minnesota’s trees are preparing for winter on the inside, too! To stay alive, they need to have a constant flow of water running from their roots to their crowns through the long, thin passages called xylem. These structures are like the veins and arteries of the tree, and they function like drinking straws: a bubble or interruption in flow can cause the whole xylem vessel to stop working. If water in the xylem freezes in the winter, it can create air bubbles (air is pushed out of liquid water when it freezes), which disrupt xylem flow. This is called “cavitation,” and must be avoided. Plants have many mechanisms to do so, including, in some species, the creation of natural antifreeze!
At Market Science, we want you to pay attention to how trees prepare for winter. So we asked visitors to become scientists and use a tool that many of us employ in our own research: “litterbags.” Fallen leaves are often called “litter,” so a litterbag is just a mesh bag filled with senesced leaves. Scientists interested in how quickly leaves decompose can put leaves of a known weight in a litterbag, leave them out in the world, and weigh the leaves after some time has passed. The rate of their decomposition can tell us about the leaves’ chemical composition and the environment where they were decomposing. Our visitors got to do this, too, by making litterbags filled with leaves from oak, pine, eastern red cedar, box elder, and basswood! These newly trained litter scientists will place their bags around their homes and yards and check them periodically to see how decomposition proceeds for their leaves of choice.
Thanks to everyone who came out to learn about the ways that MN trees prepare for winter. Two pieces of news for those who visited us:
1. In case you were wondering, maples were the runaway favorite in our poll of favorite fall foliage, beating out birches, aspens, and oaks.
2. If you brought home a litterbag, keep an eye on it as we move through winter and spring. If you take a picture of it decomposing next year and send it to Market Science, you’ll be entered in a drawing to win a tote bag. Get in touch here.
Did you know that Aegilops – the name for a genus of grasses including wild wheat relatives – is the longest word in the English language in which the letters are arranged in alphabetical order? This was just one of the many fun facts shared by volunteer scientists and educators at the Market Science booth this past Saturday at the Midtown Farmer’s Market.
An ancestral wheat head!
USDA-ARS (Agricultural Research Service) scientists Katie, Veronica, Marisa, Jitendra
We talked a lot about domestication of cereal crops this week, particularly wheat and barley. Humans began the process of cultivating these plants for use in the fertile crescent around 10,000 years ago. Some were interested to find that barley had a second point of domestication in western Asia. Modern cultivated wheat and wild species were on display to give an in-person view of how plants have been adapted to modern agriculture practices by humans. We discussed how the ancestors to both plants used to have “shattering” seeds that readily fell off the plant – this was important to spread the seeds in the wild. However, people selected for “non-shattering” plants so that all of the grains stay put until ready for harvest all at once. Market-goers were able to look under the microscope to view “shattering” versus “non-shattering” seeds, which have smooth and rough break-points from the plant, respectively.
Market-goers were able to test their knowledge of where in the world cereal grains, pseudocereals, and and grain legumes were domesticated with a fun matching game. Those who were paying attention in the first lesson were able to place wheat and barley on the map right away. Some crops were much more difficult to match to their point of origin – most were surprised that peanuts were first cultivated in the Andean region of South America!
What defines a cereal versus a pseudocereal versus a grain legume? Good question! True cereals all belong to the grass family (Poaceae). True cereals include wheat, barley, oat, rye, corn, rice, sorghum, millet, and teff. Pseudocereals are not grasses, but are used for nutritional purposes like cereal grains. These include buckwheat and quinoa. Grain legumes are subset of legume crops that are grown for consumption of their seeds. These include peanuts, soybean, and chickpea.
Budding artists had fun trying their hands at seed art. For the more scientific of the bunch, matching the grains to the proper plant was fun, while others chose to decorate farm scenes. Some market-goers even honored Prince with Purple gRAIN art. It was a great day at the Market! We hope to see you next Saturday.
On July 30, researchers from the Ishii laboratory at the University of Minnesota came out to the Market to demonstrate an innovative method for removing nitrogen pollution from water: woodchip bioreactors.
When nitrates build up in our local waters, algae blooms can develop which alter the water chemistry and make it difficult for many other animals and plants to thrive. Agriculture often needs to use nitrate-based fertilizer to grow crops, so researchers have worked to find ways to remove this nitrate from water draining off fields. Woodchip bioreactors are a sustainable method to remove up to 50% of the potential nitrate pollution!
The woodchips act as a home and food for many small bacteria (tiny organisms or microbes). As we need oxygen to breathe, the microbes use the potentially polluting nitrate and breathe out (respire) nitrogen gas (NO2), which isn’t a pollutant. Then the water can run-off to nearby streams and eventually lakes with far less nitrate!
Woodchips are a food source for the bacteria!
We looked at bacterial colonies, the microbes that do the work in a bioreactor!
The systems are constantly being improved. The Ishii lab studies the microbes to try and select bacterial types that are more efficient at removing nitrates. Other researchers study the best ways to move water through the systems. Many farms in Minnesota and elsewhere already have woodchip bioreactors in their fields.
On June 25, we had a session about the code underlying all living things: DNA! The purpose of the Genes, Genomes, and GMOs session was to demystify DNA and genetics for market goers.
Using commonly available items such as coffee filters, soap, salt and rubbing alcohol, kids and adults alike had great fun extracting DNA from strawberries. We learned that the “stringy white stuff”, aka DNA, contains genes, which determine strawberries’ shape, color, taste, and growth habit!
In order to look at DNA more in depth, another activity was DNA origami. We put our folding skills to the test, creating a spiral staircase that depicts the double helix structure of DNA. These two anti-parallel strands contain complementary information which allows the sequence to reliably be copied and passed down from one generation to the next. Want to recreate the human genome using DNA origami? Great, only 3 billion more to go!
For those wondering how it all comes together, we used a poster to show that DNA strands are coiled many times in order to be packaged into cells, and that the collection of all the genetic information in one cell constitutes a genome. The genes within a genome have natural variations among individuals, such as tall vs. small plants or red vs. yellow fruits. For thousands of years, humans have unknowingly selected the very best gene variants during the course of a crop’s domestication.
Newer technologies allow us to make targeted changes to genomes, such as the disruption of a gene, or introduction of new genes. The result? Genetically modified organisms, or GMOs. In one final activity, Erik showed us which produce items currently on the market are genetically modified, and explained which ones will be available in coming months.
by Nick Minor, Allison Haaning, and Isabella Armour
On May 28, we had a session all about birds. We used bird specimens (from the University of Minnesota’s Bell Museum of Natural History) to examine differences within a species, differences between distantly related species with shared names (American and European robins), wing coloration, and specialized beaks. We also tried our hand at identifying local Minnesota birds by sight and call, and we made bird feeders to attract local birds. Oh–and there was live red-tailed hawk demonstration from the University of Minnesota’s Raptor Center!
Out of all the animals on earth, few reconnect us to nature quite like birds do. We explored why and learned some new things along the way.
Where to start? Before we learn anything else about birds, we have to learn their names. Naming things allows us to communicate more clearly and organize collective knowledge. Bird species are often very distinct from each other, in both appearance and sound, and their names often reflect this. For example, did you know that cardinals were named for their resemblance to Catholic Cardinals, clergy members who wore long red robes and peaked hats? Bet you can guess how hummingbirds got their names!
Many common Minnesota birds can also be identified by their appearances and calls. Throughout the year, even in urban areas, there are often at least ten bird species to be found. At the right place and the right time, bird species may number up to triple digits! The ability to put names on species as we observe them furthers our awareness that we share this planet with other numerous other captivating organisms. Learn your Minnesotan neighbors from this video:
Once you look for them, birds are everywhere! In virtually any habitat from pole to pole, we can observe a rich diversity of bird species. Wherever we look, even in highly altered urban landscapes, we can find nesting house sparrows, fluttering pigeons, yammering red winged blackbirds and so much more. All we have to do is open our eyes and ears. This ubiquity makes birds the perfect plugin to the natural world no matter where you live. How could we not wonder about them when they’re always around?
With just a little effort, we can get closer to our avian neighbors. One way to do this, of course, is with bird feeders. We hosted a simple, take-home-bird feeder making station where market-goers could construct their own feeders. For instructions to make one of the bird feeders we made, visit http://www.everydaymomideas.com/2012/10/easy-bird-feeder-craft.html.
Another way to get closer to birds is with a little help from optics. Starting early in the 1900s, advances in binocular technology allowed naturalists a new way to observe species in the field – one that did not involve shooting them. Instead, naturalists could go out into the field and observe birds’ behavior as well as their plumage. Thus, a new era in nature observation was born. Along with the invention of the field guide by Roger Tory Peterson, binoculars are one of the most historically significant technologies for enhancing people’s understanding of nature. We wanted to share this with market-goers, so we brought binoculars from the Bell Museum of Natural History to demonstrate their use. Do you have a pair of binoculars at home?
Another reason why birds are so fascinating is, of course, their beauty. What could be as striking as the red of a male Northern Cardinal against the white of a snowy Minnesota winter? What could be as soothing as the song of an American Robin on a warm summer evening? Birds have aesthetically pleased us humans as long as we have coexisted with them. In birds, beauty takes on many different forms. Each of the earth’s approximately 10,000 bird species is unique, and there is even variation between individuals birds within a species. All of this variation leads to a spectacular diversity of beautiful forms, but here’s the big question: why does this exist?
We explored this diversity with some carefully selected specimens from the University of Minnesota’s own Bell Museum of Natural History. These specimens hail from around the world, each telling their own unique story and providing a treasure trove of valuable data to scientists.
We had a specimen of the diminutive European Robin to compare to the American Robin. European explorers named the American Robin after the European Robin, which shares an orange breast. But even though they are similar in appearance, 200 years later we would learn that these two “robins” are not closely related at all!
We also had a couple specimens of the Yellow-headed Blackbird, a larger relative of the familiar Red-winged Blackbird. Both specimens were females, but one lacked dark coloration. Why? Likely some genetic mutation or illness made the white female unable to produce dark pigment. But notice that she still has yellow color. This shows that this bird produces the dark and yellow colors in fundamentally different ways: the birds produce the dark color themselves but get the yellow pigment from their diet.
Some exotic, tropical specimens were also on display. We brought the extravagant Lovely Cotinga, a member of a family of birds that we might as well call South America’s birds of paradise, and the colorful Collared Aracari, a small toucan with obvious serrations on its bill for mashing up tough, tropical fruit. We also brought the metallic green Great Jacamar, which hunts large aerial insects and kills them by beating them against branches with its large bill, and a Paradise Tanager, a representative of one of the most diverse families of birds on earth.
We learned so much from our bird specimens and we explored techniques to get closer to our local birds, but we didn’t have birds stop by and check our feeders.
Representatives from the University of Minnesota Raptor Center filled in the missing piece, arriving part-way through the morning, with Jamaica, a very-much-alive Red-tailed Hawk! Red-tailed hawks live throughout much of North America, feasting on different kinds of prey in different areas, they eat a lot of small rodents, but in some parts of the US they get more adventurous: in the American Southwest they can grab rattlesnakes! We saw an example red-tail skull that showed the large eye sockets of these birds: they use eye sight as a primary hunting tool! You may often see these hawks on roadsides, where they have open space to spy prey. We learned that roadside trash is especially dangerous for hawks: mice come and snack on the trash and then hawks can be hit by cars as they swoop in for their meal.
Birds are engaging to us not only because they are everywhere, or even because they are beautiful, but because they are so very wonderfully alive. Coming in so many forms, birds have the power to get us out of our own heads, every now and again, and remind us that there are exciting, mysterious, and surprising things happening around us all the time.
And all we need to do, then, is take a step back and look.
Many thanks to all those who joined us on May 28th! Special thanks to the Minnesota Raptor Center and the Bell Museum of Natural History!
P.S. Here are some handy bird-related resources for diving deeper into birding:
http://ebird.org/ – Come here to explore local citizen science data to find species and contribute your own observations to science.
http://feederwatch.org/ – Do you have a birdfeeder? Using this citizen science project, your observations could contribute to science.
We explored how water moves through trees and explored all of the spring growth on our neighborhood trees!
Like all living things, plants need water. They use it for photosynthesis (the process of using energy from light to make sugars) and to keep their tissues hydrated. Plants, however, don’t have any organs that pump water throughout the plant. We examined sections of trees for evidence of how plants move water.
Plants move water throughout the plant in a series of pipe-like specialized cells, or xylem. Xylem tubes, or vessels, are connected to one another from the roots, through the stems, and into the leaves. We learned about how water moves through the xylem because of the Soil-Plant-Air Continuum.
For most plants, water in the soil is the source of water and roots absorb this water so that it can fill the xylem. Water moves out of the plant through the leaves. The leaves have small pores, stomata, which open to take on carbon dioxide, CO2, which the plant uses for photosynthesis. The leaves are like small bags of water, while the air outside is much more dry (not 100% humidity). As would happen if a glass of water is left outside on a warm day, water is lost to evaporation. So when the stomata on a plant’s leaves are open, CO2 comes in, while water evaporates out.
This loss of water exerts a negative pressure akin to the sucking of liquid through a straw. When the plant loses water in its leaves, it pulls more water from the xylem (in the leaf veins) and that pulls more water from the xylem in the stem, which pulls more water from the xylem in the roots, which can then absorb more water from the soil.
We also explored how this method of water movement and the seasons in Minnesota can cause tree rings. Many of us are familiar with annual rings on trees, but we explored why many trees form rings here, while they might not in other areas (like the tropics).
Trees form xylem throughout their growing season, from spring to early fall. They also have access to different amounts of water throughout their growing season. In the spring, the soil is wetter with snow melt and spring rains, while by August, it’s the air is hotter and there isn’t as much rain. Because water moves through the plant as it’s sucked out by the atmosphere, plants without much access to water can form bubbles in xylem, which stops water flow (this is somewhat similar to form bubbles in a straw when near the end of a drink). Plants can avoid that by forming smaller (thinner diameter) xylem in dry conditions. Because the trees in Minnesota form xylem of different sizes each growing season (wide in spring and thin in late summer) we can see annual rings.
Since we knew that trees are moving water and adjusting their xylem cells sizes to the environment, we could understand that trees are really dynamic, living organisms. We examined some local tree twigs to find flowers and cones and to see leaves and young wood up close.
We didn’t have many twigs with only buds to examine because our neighborhood trees leafed out a bit earlier this year than last, possibly because we had a very warm spring. Buds contain tissue that forms or expands into the first leaves and flowers of spring. They overwinter on the trees. There are several factors that cause the formation: the trees here in Minnesota form buds in response to a shortening day length and longer night length (and sometimes cooler temperatures) which indicates the onset of later autumn and winter. Trees have a method of tracking cold days during the winter and once they have experienced enough cold days, they will then begin to expand buds when temperatures warm. This can be a problem if temperatures warm too early and new leaves experience a frost. Plant buds also sense lengthening days and can leaf-out in response to the longer days of spring.
We explored how plants move water and looked for evidence in leaves and stems. We also learned that tree rings tell us more than a tree’s age: they also show the transition from wet to dry environmental conditions. We then check out what trees in our neighborhood were doing in response to a warm spring.
Every market-goer is using botanical skills. We analyze whether we’re looking at tomatoes or tomatillos, cucumbers or zucchini, whether we should get the leafy kale or the very green chard. We learn to recognize to different fruits, roots, flowers, stems—even if we don’t know the specifics of plant anatomy. Botanists, or plant scientists, do the same thing in our studies, examining differences between plants and the parts of plants to learn about plant taxonomy (or relationships), plant ecology (where plants live and how populations change), and basic plant biology (how plants develop, grow, and reproduce). For our Botany of the market week, we looked at the market as botanists would.
We examined produce from all over the world, with the help of a lot of plant materials donated by the University of Minnesota College of Biological Sciences Conservatory (go visit! it’s open to visitors on weekdays!). We looked at plants sold at our market and unfamiliar plants common at markets elsewhere—like yucca root or dragon fruits. We also saw the leaves and stems of plants that produce food we only see a bit of at our grocery stores: cinnamon leaves (we use the bark for spice) or black pepper vine (we grind up the dried fruits).
We saw on a map that the plants that are grown in Minnesota and sold at our market are mostly from cooler climates all over the world, while plants not grown here tend to be from warmer climates.
We also examined the relationships of the plants we eat. Tomatoes and potatoes are very closely related—they are both the same genus Solanum, but just different species. We eat different parts of those plants. Peppers are in the same family, but different species and genera (two different genus groups). We saw an example of a group of very different looking produce that are actually all the same species: broccoli, kale, Brussel sprouts, cabbage, cauliflower are all from a single wild species Brassica oleracea.
When we eat all those Brassica oleracea cultivars, we’re often eating different parts of the plant. Sometimes different plant parts offer different benefits to the eater: we can get more starch often from storage anatomical features: modified stems, like potatoes which are tubers , or roots. We get sweet sugars often from fruits: berries like oranges or drupes like plums. We also eat plant parts that we don’t expect: we eat the developing flowers of broccoli and the leaves of onions and the petioles or leaf stalks of celery.
We also learned how we use terms in everyday life that are different than how botanists would describe plants and plant parts. We could see under a microscope that raspberries are actually a bunch of connected fruits (actually fleshy and single-seeded, called drupes) and strawberries show their fruits as the tiny seed-like structure (fruits called achenes) on the outside of the red flesh. Tomatoes and chile peppers are also true berries!
Next time you’re at the grocery store or market, see if you can identify all the different plant parts we eat: roots, stems, leaves, fruits, and seeds.
Plant Biological Sciences graduate students from the University of Minnesota were at the market this past Saturday to share their knowledge about plant breeding. Pretty much all of our modern-day crops and ornamental plants have been selectively bred for higher yield, better taste, prettier flowers, or a number of other beneficial characteristics.
We learned about how hybridization is used to create new varieties of tomatoes and even observed step-by-step under a microscope how tomato hybrids are created. We saw how a plant breeder would identify potential fruit-bearing flowers on the mother plant and carefully dissect the flower, leaving only the stigma. Then pollen harvested from the father plant is applied to the dissected flowers, so the new tomatoes bear seeds that are the hybrids of both the mother and father plants. Hybrid plants might have desirable characteristics from both parents.
We also got a sneak peek (and taste!) of a new high-yielding, early maturing tomato variety that is being developed specifically for cold northern climates by Professor Changbin Chen at the University of Minnesota, Department of Horticultural Sciences.
Most modern crops are derived from wild plants, so we also featured a collection of barley that showed the progression of barley breeding from smaller, leafier, wild relatives to large-seeded cultivars, varieties that have been specifically bred for high yield and other important characteristics, like malting qualities.
At the next market, we’re focusing on one particular crop that’s been bred from a wild North American plant: corn! See how cultivation has lead to delicious fruit, sugary snacks, and even compostable plastics at the Festival del Maíz!
We learned about how topography can affect water flow and how water flow can influence topography. Many people donned 3-D glasses to examine a shaded topographic map that showed the mountains, river valleys, and undersea landforms of the whole globe. We saw undersea trenches, tall mountains, and the Mississippi River Valley. Then we used the U of St. Thomas’s stream simulator that allowed us to interact with water flow on a landscape and examine the processes that shaped those landscapes. We made eddies, formed potholes, and tried out sediment levies.
We tried our hand at paleolimnology, or the study of the history of lakes. We learned that soil cores from lake bottoms, or beds, can reveal the environmental history of the area. Sediment appearance changes with the seasons and can be examined to show the historical climate of the area using chemical analyses, pollen counts, and many other techniques. Some of the scientists were using the chemistry of shells in different lake sediments to reconstruct temperatures! We also looked at diatoms that are commonly found in lakes and sediments in Minnesota. Diatoms are algae with silicate (glass!) shells and their shells remain in soil and lake sediment after they die.
We also looked at different types of rocks to learn about the geology of Minnesota. We examined the difference between sedimentary and igneous (volcanic origin) rocks with hand lenses and microscopes. We tried to determine whether the rock was quickly cooled or slowly cooled based on the size of crystals (bigger crystals result when rocks are slowly cooled). We examined how metamorphic rocks are different from their composite parts (both igneous and sedimentary).
Finally, we took all of our new-found geologic knowledge and mixed it with googly eyes to make fine art! Thanks again to Dr. Kevin Thiessen and the scientists from University of St. Thomas. We had a total of 188 visitors this week (76 kids, 112 adults, and 118 people stayed long enough to alter hydrology and examine rocks or make their own pet).