If spicy fruits are helpful to a chili plant, why aren't all chili peppers hot? (courtesy of flickr user dbeck03)

When we last saw University of Washington ecologist Joshua Tewksbury, in the April 2009 issue of Smithsonian, he was bouncing along the back roads of Bolivia, accompanied by our writer Brendan Borrell, in search of chili peppers. He was hoping to answer what should have been a simple question: Why are chilies spicy?

Capsaicin, the molecule that gives chilies their heat, it turns out, helps protect chili fruits from fungal rot and munching rodents without deterring the birds that the plant needs to distribute the seeds in the fruit.

But that leads to a new question—why aren’t all chili peppers hot? Tewksbury’s lab has an answer to that, too, in a study published last month in the Proceedings of the Royal Society B.

David Haak, then a graduate student in Tewksbury’s lab and now a post-doc at Indiana University, studied Capsicum chacoense, a species of wild chili in Bolivia that occurs either in populations of only hot chilies or in mixed populations with hot and mild fruits. Haak, Tewksbury and their colleagues found that in the wettest parts of their research area, only hot chilies grew. The driest places, though, were home to mixed populations, with only 15 to 20 percent of the plants producing spicy fruits.

The researchers collected hot and mild fruits from three sites in their study area, spanning the range of rainfall and  population types. They grew the seeds in the lab, giving the plants either plenty of water–mimicking the wettest areas in which the plants grew–or not enough water, as in the dry areas.

Both mild and spicy plants grew well when there was plenty of water, the researchers found. And there was no cost to producing lots of capsaicin–spicy plants produced just as many seeds as mild ones. But because Fusarium, the fungus that attacks chili plants in Bolivia, likes wet conditions, the mild plants would be more vulnerable and not able to survive. That’s why spicy chilies dominated the wetter areas of Bolivia, Haak and his colleagues concluded.

When the plants were subjected to drought-like conditions, though, spicy plants produced only half the number of seeds as the mild ones. GrrlScientist at Maniraptora: Tastes Like Chicken explains:

Plants lose water through microscopic pores in their leaves and stems, known as stomata. During the day, plants release oxygen to the environment in exchange for carbon dioxide through their stomata, but this vital gas exchange comes at a price: water loss. Knowing that the density of stomata on a plant’s leaves directly affect water loss, the team compared stomata density from 30 age- and height-matched pungent and non-pungent chili plants.

They found that pungent plants have a 40 percent greater stomata density on their leaves than do non-pungent plants. Even after cross-breeding pungent with non-pungent plants and then identifying whether the fruits were pungent, the team found that the pungent crossbred chilis still had a greater stomata density than non-pungent crossbreds.

Because the spicy plants lose more water, they’re not able to produce as many seeds. And with Fusarium not as big of a problem in the dry conditions and the mild plants’ greater ability to hold onto water and produce more seeds, those plants are able to thrive in the driest conditions and easily outgrow their spicy brethren there.

Aspen trees in Colorado (courtesy of flickr user Bill Dayton)

Three years ago, Michelle Nijhuis wrote about the phenomenon of sudden aspen decline (SAD) in her story “What’s Killing the Aspen?”

In 2004, foresters noticed that aspen in western Colorado were falling silent. While the trees have always been susceptible to disease and insect attacks, especially in old age, “this was totally different from anything we’d seen before,” says forester Wayne Shepperd. “In the past, you’d maybe see rapid die-off of one stand out of an entire landscape—it wasn’t really a big deal. But now, we’re seeing whole portions of the landscape go.”

By 2006, close to 150,000 acres of Colorado aspen were dead or damaged, according to aerial surveys. By the following year, the grim phenomenon had a name—”sudden aspen decline,” or SAD—and the devastated acreage had more than doubled, with some 13 percent of the state’s aspen showing declines. In many places, patches of bare and dying treetops are as noticeable as missing teeth, and some sickly areas stretch for miles. Aspen declines are also underway in Wyoming, Utah and elsewhere in the Rockies. Surveys of two national forests in Arizona showed that from 2000 to 2007, lower-elevation areas lost 90 percent of their aspen.

At the time, scientists suspected that extreme drought and high temperatures in the West, probably due to climate change, were weakening the trees.

It seems that new stems aren’t growing back after trees die because drought and heat have stressed the trees. During drought, aspen close off microscopic openings in their leaves, a survival measure that slows water loss but also slows the uptake of carbon dioxide, required for photosynthesis. As a result, the trees can’t convert as much sunlight into sugar. [Forest Service plant pathologist Jim] Worrall speculates that the trees absorb stored energy from their own roots, eventually killing the roots and preventing the rise of new aspen sprouts. “They basically starve to death,” he says.

But a new study in PNAS has found that it was lack of water, not food, that led to the aspen deaths. Nijhuis explained the findings on the blog The Last Word on Nothing:

When the researchers studied dying aspen in the field in Colorado, and induced drought stress in both potted aspen and full-grown trees, they found that the aspen hung on to plenty of carbohydrates. The problem was that the water-delivery systems in the trees’ roots and branches were blocked with air bubbles, like straws trying to pull water from too-shallow pools. … When trees lose 50 percent of their water-delivery capacity, they start to drop their leaves, no matter the season; the dying aspen in the study had lost 70 to 80 percent. And the more root blockage, the researchers found, the more root death. Aspen are a clonal species, and without healthy roots, they’re slow to resprout and recover.

The weakened trees are more vulnerable to other threats, such as insects and fungal infections, Nijhuis noted both in 2008 and in her recent post.

“Our study provides a snapshot of what future droughts could hold for the emblematic tree of the American West,” says the study’s lead author, William Anderegg of Stanford University. The study holds an even greater lesson, though, when it comes to climate change. As we pump more and more greenhouse gases into the atmosphere, the American West and many other places are expected to get drier. And that lack of water may hurt other tree species, animal species and humans, too.

Hawkmoths prefer columbines with long, slender spurs. (Courtesy of Scott A. Hodges/UCSB)

Adaptive radiation is a principle in evolutionary biology in which one species, in response to opportunities in its environment, quickly adapts and develops new traits and diversifies into many species. An example of adaptive radiation is found in columbine flowers (genus Aquilegia), a group of about 70 species that have nectar spurs extending from the base of the flower petals. What makes these spurs special is that each species has spurs of a different length, seemingly tailored to that species’ pollinator, whether it be a hummingbird, hawkmoth or bee.

Scientists since Charles Darwin have observed similar examples of adaptive radiation but have been unable to describe what happens on a cellular or genetic scale. “Darwin, observing orchids, recognized that the extraordinarily long nectar spur on the Angraecum must have evolved in concert with the equally long tongue of the moth that pollinated it, but the exact mechanism for this kind of adaptation has been a matter of speculation,” says Sharon Gerbode of Harvard University.

Gerbode and her colleagues at Harvard and the University of California at Santa Barbara investigated that mechanism in columbines and report their findings in the Proceedings of the Royal Society B. For decades, scientists had thought that the differences in nectar spur length were due to the number of cells in the nectar spur. But when the researchers counted the number of cells and calculated the area and degree of elongation of each cell–which required more than 13,000 measurements across several species–they found that the assumptions were wrong. Nearly all of the difference in spur length can be attributed to the length of the cells.

In each species, cell division in the nectar spur stops when the spur is about 5 millimeters long. Then the spurs begin to elongate, and how many days they spend growing determines the eventual length of the spur.

“Now that we understand the real developmental basis for the first appearance and diversification of spurs, we can make more informed guesses about what genes contributed to the process,” says study co-author Elana Kramer. Further research should give the scientists insight into the genetic basis behind the radiation of this genus.

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Internal parts of a wildflower, magnified 100x, by Arik Shapira of Hod HaSharon, Israel (Nikon Small World)

The Nikon Small World Photomicrography Competition is always a favorite in my office. The imagery—created with any of a number of techniques that magnify and enhance objects—ranges from the fantastical to the freaky, but it often has the added benefit of being useful in scientific research. This year Nikon, which announced the 2011 winners earlier this month, has added a Popular Vote feature, which is open until October 30 (the photo above is currently near the top of the leaderboard). And if you have an amazing photomicrograph or digital video (a new category for 2012), you can find rules and entry forms here.

But I can hardly talk about a photo contest without mentioning Smithsonian magazine’s own 9th Annual Photo Contest. You can enter images in one of five categories—Altered Images, Americana, the Natural World, People and Travel—and even if you don’t make the finals, your photo may be featured as one of our daily Editor’s Picks online. The contest is open until December 1, 2:00 p.m. EST, and finalists will be announced on March 1, 2012.

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Most orchid bees, like this Euglossa paisa, have metallic coloration (credit: S. Ramirez, 2005)

When scientists delve into studies of the co-evolution of plants and their pollinators, they have something of a chicken/egg problem—which evolved first, the plant or its pollinator? Orchids and orchid bees are a classic example of this relationship. The flowers depend on the bees to pollinate them so they can reproduce and, in return, the bees get fragrance compounds they use during courtship displays (rather like cologne to attract the lady bees). And researchers had thought that they co-evolved, each species changing a bit, back and forth, over time.

But a new study in Science has found that the relationship isn’t as equal as had been thought. The biologists reconstructed the complex evolutionary history of the plants and their pollinators, figuring out which bees pollinated which orchid species and analyzing the compounds collected by the bees. It seems that the orchids need the bees more than the bees need the flowers—the compounds produced by the orchids are only about 10 percent of the compounds collected by the bees. The bees collect far more of their “cologne” from other sources, such as tree resin, fungi and leaves.

And it was the bees that evolved first, the researchers found, at least 12 million years before the orchids. “The bees evolved much earlier and independently, which the orchids appear to have been catching up,” says the study’s lead author, Santiago Ramirez, a post-doc at the University of California at Berkeley. And as the bees evolve new preferences for these chemical compounds, the orchids follow, evolving new compounds to lure back their bee pollinators.

But this study is more than just an interesting look into the evolution of two groups of organisms. The researchers note that in the context of the current decline of bee populations worldwide, their research has disturbing implications for what that decline might mean for plants. “Many of these orchids don’t produce any other type of reward, such as nectar, that would attract other species of bee pollinators,” Ramirez notes. “If you lose one species of bee, you could lose three to four species of orchids.”

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Sweet sorghum may be grown for biofuel (courtesy of flickr user Pethan)

If one of the goals of growing plants for biofuel is to be kinder to the environment than you are by extracting oil from the earth, you wouldn’t want to plant anything that could be harmful to the environment. But how could a plant harm the environment? Well, it could become invasive, outcompeting native species, altering the habitat and driving other species into extinction. The damage from and control of invasive plants already costs the United States more than $34 billion each year, according to one estimate. Bioenergy shouldn’t add to that number.

Recognizing this potential for danger, a group of biologists at the University of Florida recently set out to predict whether a dozen species being considered for biofuel cultivation could become invasive. Their study appears in Biomass and Bioenergy.

The researchers note that the characteristics that make a plant attractive as a biofuel source—high productivity, low input requirements, wide breadth of habitat—overlap with those of non-native invasive species. And when the biologists analyzed a dozen non-native species using an assessment system already used by Australia and New Zealand for more than a decade, only four species (miscantus, plume grass, sugarcane and sweet sorghum) had acceptable scores. Seven other species were rated as likely to become invasive, and the last needed further evaluation.

These results may be surprising to the people who proposed these species as biofuels because nearly all of the plants have been grown in Florida for decades for ornamental or agricultural purposes. And they may think, therefore, that this study can be ignored. But growing a tree in a garden is not the same thing as growing acres of them for regular harvesting. “Cultivation of large acreages of a species previously cultivated and introduced in low numbers over relatively low acreages, might so significantly alter propagule press that shifts in dispersal and colonization frequency occur,” the scientists write. In other words, growing something in large numbers can create the opportunities necessary for the species to take off and grow in even larger numbers in places you never intended.

And that has happened in the past. In Australia, for example, people grew a type of ornamental tree called Mimosa pigra for at least 60 years with no problems. But when the tree was moved to a new riparian habitat—the land near rivers or streams—the tree quickly became invasive; it’s now one of Australia’s worst invasive plants.

Not that long ago biofuels were touted as the easy solution to our energy future. We now know that’s not the case. And this study shows that it’s even more complex that we thought.

A photo montage of a Marcgravia evenia flower, with its nectaries below and dish-shaped leaf above, along with a Glossophaga soricina bat (image courtesy of Ralph Mangelsdorff and Ralph Simon)

Flowers have evolved many strategies for attracting pollinators—bright colors, guiding patterns, interesting scents, brilliant mimicry. The Cuban rainforest vine Marcgravia evenia has a different strategy, though. Scientists have found that the vine has one or two specially shaped leaves hanging near its flowers that act as a bat signal, luring these flying mammals. The bats get a meal, and the flowers get pollinated. (The study appears in this week’s Science.)

The leaves have a concave shape, somewhat like a dish reflector. When researchers sent a sonar signal towards such a leaf, they found that they received back strong echoes that a bat would find easy to identify. The scientists then trained nectar-feeding Glossophaga soricina bats to find a small feeder among foliage; when they placed a replica of the special leaf near the feeder, the bats were able to find it twice as fast.

Having such a leaf does have a downside for the plant—it isn’t as well-suited for photosynthesis as more traditional leaves on the vine and thus creates less energy for the plant. But the scientists argue in their paper that “these costs are outweighed by the benefits of more efficient pollinator attraction.” In other words, the plant’s need for sex is greater than its need for more food.

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Scientists use satellite images of the kelp canopy (here, as seen from underwater) to track this important ecosystem over time (Credit: Stuart Halewood)

I remember an analogy from one of my marine science classes, that studying the ocean is sometimes like trying to study a forest by dropping a bucket from a helicopter. It explains why we know comparatively little about ocean ecosystems, even when they’re situated close to populous areas of land, like the forests of giant kelp (Macrocystis pyrifera) in the Santa Barbara Channel off California. These kelp ecosystems are important because they provide food and habitat for a variety of fish and other species. And now a group of scientists led by the University of California, Santa Barbara found a new way to study the kelp, which enabled them to look at long-term changes in this ecosystem for the first time. (Their results appear in Marine Ecology Progress Series.)

The scientists were able to use images of the area made by the Landsat 5 satellite from 1984 through 2009. (Scientists were not previously able to use the extensive collection of imagery because of the cost; in 2009, Landsat images were made freely available.) “Giant kelp forms a dense floating canopy at the sea surface that’s distinctive when viewed from above,” the researchers wrote. They used the imagery to document the changes in the kelp forests over time and found that, during most years, the forests go through an annual cycle, rapidly growing in spring and summer and dying back during the winter. In some regions, huge waves limit the kelp’s growth, while in others they are held back by a lack of nutrients.

“We know from scuba observations that individual kelp plants are fast-growing and short-lived,” says study co-author Kyle Cavanaugh of UCSB. “The new data show the patterns of variability that are also present within and among years at much larger spatial scales. Entire kelp forests can be wiped out in days, then recover in a matter of months.”

Kelp biomass off Santa Barbara, 1984-2009, as measured by the Landsat 5 satellite (Credit: NASA; SBC LTER Site)

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Cambridge University Botanic Garden, Cambridge, England (photo by Sarah Zielinski)

I may have grown up in the countryside, but I am more than content with my life as a city girl. That said, I find myself drawn to green spaces; for example, my vacations more often than not include trips to botanic gardens. And I like to walk to work when the weather’s nice, taking advantage of Washington’s quiet, tree-lined streets, sometimes cutting through a couple of parks and a public garden.

I’m getting more than simple enjoyment (and great pictures) out of these parks and gardens—it turns out that they may convey whole array of benefits, as explained in “Parks and Other Green Environments: Essential Comp. of a Healthy Human Habitat” (pdf), a recent report from the National Recreation and Park Association. (And what better subject to talk about on Earth Day?) Some highlights:

* A study that compared census tracts in Los Angeles found that people who had more parks reported higher levels of trust and a greater willingness to help each other.

* In a Dutch study of more than 10,000 households in the Netherlands, the less green a person’s environment was, the more likely there were to be lonely or report a lack of social support.

* In low-income housing projects, residents who have views of only concrete and more buildings report more violence and aggression than residents who have a view of trees and grass. Thefts, burglaries and arson are all more common when vegetation is scarce.

* Japanese researchers found that just 15 minutes of walking in a forest environment resulted in less stress along with lower cortisol levels, pulse rate and blood pressure.

* Employees who have a view of trees from their desks report less job stress and more job satisfaction.

* Children who live in greener environments are more resilient and better able to cope with stressful life events, such as divorce.

* In another study, children with attention deficit/hyperactivity disorder had better concentration after a 20-minute walk in the park than if that walk had been taken through a neighborhood or downtown setting.

* Children in greener neighborhoods also weigh less and gain less weight than similar children in less green neighborhoods.

* A study of elderly people in Sweden found they had better concentration after an hour in the garden than if they had spent that hour in their favorite indoor room.

* A 1984 study of surgical patients in a Pennsylvania hospital found that those who had a view of trees and grass recovered faster, with fewer complications and able to rely on lower-strength pain medications.

* Several diseases are less prevalent in greener neighborhoods, including depression, asthma, stroke and migraines.

* In the places with the fewest green spaces, the poorest people die at twice the rate of the richest, but where green space is common, that is lowered to only 1.43 times the rate of the rich.

Study after study shows that greening our urban environment is important, that it can lead to less crime, less stress and better health. More than half the world’s people now lives in urban areas, and by 2030 nearly 70 percent will do so. But, worryingly, our urban spaces are becoming less green, not more. So what’s to be done? It’s easy: build more parks, plant more trees, don’t get rid of what we already have. And take advantage of what’s outside.

A fly caught in a Venus flytrap (courtesy of flickr user rore)

You might think that a plant that eats things should be able to take care of itself, but the sad fact is that more than half of the carnivorous plant species evaluated by the International Union for the Conservation of Nature (IUCN) are listed as either vulnerable, endangered or critically endangered. A new study in the journal Biological Conservation examined the threats faced by 48 species of these plants and provides some insight into what’s going on.

Many of the threats are familiar to anyone who has been following the tales of species declines—habitat loss due to the expansion of agriculture tops the list, and pollution and modification of natural systems (such as fire suppression) were also big factors. But carnivorous plants faced another, almost unique threat—that of poaching. Pitcher plants and Venus flytraps are the most likely types to be affected by collectors, the researchers found. “Even though there are good alternatives, such as growing them in greenhouses or labs, people who are after a quick fix will just go out and take them because it can take several years for the plants to reach a decent size,” study co-author David Jennings, of the University of South Florida, told the BBC News.

The scale of the poaching can be devastating, as Smithsonian documented last year in “The Venus Flytrap’s Lethal Allure“:

Always rare, the flytrap is now in danger of becoming the mythical creature it sounds as if it should be. In and around North Carolina’s Green Swamp, poachers uproot them from protected areas as well as private lands, where they can be harvested only with an owner’s permission. The plants have such shallow roots that some poachers dig them up with butcher knives or spoons, often while wearing camouflage and kneepads (the plants grow in such convenient clumps that flytrappers, as they’re called, barely have to move). Each pilfered plant sells for about 25 cents. The thieves usually live nearby, though occasionally there’s an international connection: customs agents at Baltimore-Washington International Airport once intercepted a suitcase containing 9,000 poached flytraps bound for the Netherlands, where they presumably would have been propagated or sold. The smuggler, a Dutchman, carried paperwork claiming the plants were Christmas ferns.

Carnivorous plants aren’t just weird, wacky and wonderful, but they also have important roles in their ecosystems. The loss of a carnivorous plant could easily lead to the extirpation of other creatures that rely on them (there are some species of pitcher plants, for example, that are refuges for amphibians). These plants can be incredibly useful to us, too, since they consume human pests, such as midges and deerflies, that can carry disease. And in my view, anything that eats those damn mosquitoes that devour me in summer is worth preserving.

So I hope you’ll take the scientists’ research to heart, and if you see a carnivorous plant in the wild, leave it alone.

Leefructus mirus, a 125-million-year-old fossil of a flowering plant, found in Liaoning province, China (credit: Zhiduan Chen)

Smithsonian readers may recognize the Liaoning province of China as the place where amazing fossils of bird-like dinosaurs have been found:

In a pine forest in rural northeastern China, a rugged shale slope is packed with the remains of extinct creatures from 125 million years ago, when this part of Liaoning province was covered with freshwater lakes. Volcanic eruptions regularly convulsed the area at the time, entombing untold millions of reptiles, fish, snails and insects in ash. I step gingerly among the myriad fossils, pick up a shale slab not much larger than my hand and smack its edge with a rock hammer. A seam splits a russet-colored fish in half, producing mirror impressions of delicate fins and bones as thin as human hairs.

One of China’s star paleontologists, Zhou Zhonghe, smiles. “Amazing place, isn’t it?” he says.

One of the latest finds from this province is this 125-million-year-old fossil of a flowering plant, Leefructus mirus, the earliest intact fossil of a eudicot, a familiar group of plants that includes modern maple trees and dandelions. It’s easy to see, almost as if someone had outlined it all in marker, the plant’s single stem, five leaves and a flower nestled in the middle. The plant is 6.3 inches tall and the fossil is so clear that even the flower petals are apparent. Most information about the evolution of plants during this time comes from fossilized pollen, which makes this discovery even more special.

“This fossil opens up a new way of thinking about the evolution of the first flowering plants,” said Indiana University biologist David Dilcher, one of the co-authors of the Nature paper describing the find. “We are also beginning to understand that the explosive radiation of all flowering plants about 111 million years ago has had a long history that began with the slower diversification of many families of eudicots over 10, perhaps 15 million years earlier.”

Once flowering plants evolved, they came to dominate our landscape. Evolutionary biologists are interested in how that happened, especially since it led to the diversification of other non-plant species, including pollinators and seed-eaters.

When Leefructus was alive, bees hadn’t yet evolved, but scientists think that flies, beetles or other pollinators could have taken up that role for this flower. “Leefructus was found in the volcanic ash beds of an ancient lake,” Dilcher said. “I think it was living near a lake, perhaps in a wet or marshy area much as buttercups do today.”

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A fly pollinating a Satyrium pumilum orchid (Credit: Dennis Hansen)

Scientists studying a South African orchid determined, with the clever use of roadkill, that the flower attracts pollinators by mimicking the scent of carrion. Their report appears in the Annals of Botany.

The Satyrium pumilum orchid grows in sandy, moist soil near streams in South Africa. Unlike most flowers, S. pumilum doesn’t have any nectar that would attract pollinators. But the flowers do somehow attract flies. And when the scientists placed near the orchids the carcass of a rock hyrax retrieved from a roadside, they found that a lot of the flies were carrying orchid pollen.

Further experiments revealed that the orchids were indeed producing a carrion-like scent, though it was relatively weak. But that was the perfect amount to attract flesh flies that prefer small carrion. The scent is close enough to the real thing that female flesh flies will sometimes even deposit their larvae on flowers instead of in a dead animal.

“What we’ve done is show for the first time that carrion-mimicking flowers are highly sophisticated tools for orchids,” said the study’s lead author, Timotheüs van der Niet of the University of KwaZulu-Natal in South Africa. “It also disproves a cliche—you don’t always catch more flies with honey.”

Why do the needles fall off a live Christmas tree? (photo courtesy of flickr user the jof)

Putting up a live Christmas tree can be a lot of work. You have to make sure that the tree has plenty of water, sometimes having to crawl beneath the branches while trying not to dislodge any of the breakable ornaments. And then there’s the clean-up. No matter what you do, the tree is going to shed needles destined to become lodged in the bottom of your foot. Now scientists from Canada, reporting in the journal Trees, have figured out why those needles fall off, and they’ve come up with a couple of solutions that could keep needles on longer.

There are plenty of myths advising how you can better keep the needles on your tree. When the Mythbusters tested several of them—adding fertilizer, Viagra or bleach to the water, for example, or coating the entire tree with hairspray or polyurethane—most of the home remedies weren’t much help, or they turned the tree a sickly color. But these solutions don’t address what the scientists now say is the cause of the needle loss: ethylene, a plant hormone. That’s the same molecule that ripens many fruits, and the reason why adding a ripe banana to a bag full of green tomatoes will turn them red. In the balsam fir trees of the recent study, ethylene is produced around 10 days after the tree is cut and signals to the tree that it should drop its needles. And by 40 days after cutting, the branches were bare.

The researchers then tried two ways of interfering with the ethylene. First they added 1-methylcyclopropene (1-MCP) gas to the chamber where they had put cut fir branches in water. Needle retention rose to 73 days. 1-MCP blocks ethylene receptors in the cell and is used by ornamental horticulture and apple industries to prolong the life of their products, and it could be used during the transport of Christmas trees from field to market.

In their second test, they added amino-ethoxyvinylglycine (AVG), which inhibits the production of ethylene, to the water in which the fir branches sat. Needle retention rose to 87 days. Because AVG can be easily dissolved in the tree’s supply of water, it’s more likely to find use in the home.

The scientists caution that they have yet to scale up their experiment from single cut branches to whole trees, but “what is really encouraging is that we managed to double the needle retention period of the branches,” says study co-author Seeve Pepin of the Universite Laval.

Could the same dryer sheets that keep your towels fresh and static free also repell bugs? (image courtesy of flickr user missmac)

It’s a modern old-wives tale: put a Bounce dryer sheet in your pocket while gardening and it’ll keep away the mosquitoes or gnats. This may seem a bit far-fetched to those of us who have never tried it, but researchers have now found that there could be some truth in it, when it comes to gnats, anyway.

The scientists, who published their findings this month in the journal HortScience, set up a simple experiment consisting of a large plastic container connected to two smaller plastic containers, one of which had a piece of a dryer sheet. Fungus gnats were placed in the center container and then the scientists checked where they were two days later. Each time they repeated the experiment, they found that the gnats tended to hang out in the two dryer-sheet-free containers.

In the second part of their experiment, they analyzed the chemical content of the dryer sheets with gas chromatography and found two substances that might be keeping away the gnats. The first was linalool, which is naturally found in lavender and basil and which cosmetic and perfume companies use in their products for its flower-like odor. Linalool is toxic to some types of insects, though it isn’t known to have any repellent qualities. The second compound was beta-citronellol, which is found in citronella and repels mosquitoes.

The researchers haven’t yet tested the distance over which the dryer sheets repel the gnats or whether they also repel mosquitoes, but it is interesting to see that the myth may be true. And perhaps I’ll try tucking a dryer sheet in my back pocket next year during mosquito season—it’s certainly easier than applying bug spray.

Atropa belladonna, the deadly nightshade, is just one of many plants that can kill (photo courtesy of flickr user NapaneeGal)

I have to laugh anytime I see a product label claiming that something is “all natural,” as if everything that is man-made is dangerous and all that is not is perfectly safe. Not that I’m claiming there are no synthetic evils, but there’s plenty of deadly natural items out in the world. Let’s start with this list:

1 ) Asbestos: A fibrous mineral once used for making fireproof materials. There were reports from as early as the first century A.D. that workers who came in contact with the material developed lung disease, but it wasn’t until 1989 that the EPA banned its use. Inhalation of asbestos fibers causes a host of serious diseases, including a rare form of cancer called mesothelioma. Fear of the substance runs so high that the California State Senate passed a bill earlier this year that would defrock its state rock, serpentine, because it can harbor asbestos.

2 ) Arsenic: Atomic number 33, it sits just below phosphorus on the periodic table. It was once used to treat syphilis and applied topically to whiten skin. Symptoms of arsenic poisoning start with headaches and confusion and progress to vomiting, hair loss and convulsions, resulting in coma and/or death. Sadly, groundwater throughout Bangladesh is contaminated with arsenic, leading to widespread poisoning. It is estimated that up to 20 percent of deaths in the country are the result of drinking arsenic-laced water.

3 ) Snake venom: This modified saliva contains a host of chemicals that act to kill or disable prey. Snake bites kill 20,000 people in developing countries each year. And snakes aren’t the only venomous species: there are hosts of insects, fish, reptiles and mammals (even a venomous shrew) that can kill with chemical warfare.

4 ) Botulism: The soil bacterium Clostridium botulinum produces neurotoxins that cause paralysis. Modern science has harnessed that feature to eliminate wrinkles on the faces of an aging population. The disease is relatively rare, but it kills 5 to 10 percent of those who become infected.

5 ) Plants: There are too many deadly plants to name here (if you want a good list, check out the book Wicked Plants). But there are good reasons why you shouldn’t go through fields or forests eating anything you find.

6 ) Mercury: The pretty liquid metal fascinated for centuries until the mid-1800s, when it was found to be toxic. Now school principals freak out whenever someone drops a mercury thermometer and pregnant women are advised to limit fish consumption. The element can damage the central nervous and endocrine systems and kidneys and other organs.

7 ) Ionizing Radiation: Types include alpha- and beta-decay, X-rays and gamma rays. These subatomic particles and electromagnetic waves have enough energy to strip atoms of electrons, which causes damage to DNA (at high enough levels, it kills instantly). Natural sources include radon and uranium.

8 ) Cosmic Rays: These high-energy particles come mostly from faraway supernovas. They cause damage to DNA, similar to ionizing radiation, causing cancer, cataracts and other health problems. They’re not a problem on Earth, because we have the atmosphere and magnetic field to shield us. But if we want to send anyone to Mars or beyond, we’ll have to figure out how to protect them on the long journey.

9 ) Formaldehyde: This chemical—composed of carbon, hydrogen and oxygen—is formed during the burning of methane. Up to 90 percent of all the formaldehyde on Earth may originate in the atmosphere. It is used in the synthesis of many other chemicals, as a disinfectant and as a preservative. Though it is now known to be a human carcinogen, it is still widely used.

10 ) Anthrax: This illness, caused by the bacterium Bacillus anthracis, is lethal in most forms to humans, who usually contract it from livestock. This is just one more example of a microbe that can kill—the list is far too long to even attempt.