Researchers have been hard at work in the past year on projects aimed at helping gardeners understand and grow plants better.
Let’s take a look this week at five interesting recent finds:
Future weeds lurking on our doorstep
Invasive plants (i.e. weeds) have been on the upswing lately as a threat to take over desirable plants, out-compete farm crops, and disturb the fragile health of ecosystems.
It’s only going to get worse as climate change allows new invasives to move into areas where they previously couldn’t thrive, concludes a study by researchers at the University of Massachusetts.
Pennsylvania is in the crosshairs.
“The mid-Atlantic region of the eastern United States will remain a hot spot of plant invasion with the potential addition of dozens of new species,” writes Dr. Bethany Bradley, a professor in UMass’s Department of Environmental Conservation in a paper published in “Invasive Plant Science and Management.”
Bradley and Justin Salva reviewed 674 research papers on 104 plants, then scored each on their potential negative impact, including invasiveness as well as economic impacts. The researchers also looked at state-by-state impacts into the year 2050.
Pennsylvania’s outlook includes seven plants in the top alert category, including giant reed grass (Arundo donax), a tall, corn-like ornamental grass that’s planted in some home gardens as an ornamental. That plant is already on the Pennsylvania Department of Agriculture’s invasive-plant “watch list.”
Other high-alert future weeds on the study’s Pennsylvania list include: Athel tamarisk (Tamarix aphylla), a tall shrub; roundleaf chastetree (Vitex rotundifolia), a tall shrub; shoebutton ardisia (Ardisia elliptica), a flowering broadleaf evergreen; crimson fountain grass (Cenchrus setaceus), a perennial ornamental grass; panic veldtgrass (Ehrharta erecta), a hardy grass, and French broom (Genista monspessulana), a shrub.
Bradley says it’s important to identify tomorrow’s threats now because “eradication of new invasive plants is only feasible when populations are small.”
The research is also useful to state invasive-plant advisory boards, such as the Pennsylvania Governor’s Invasive Plant Council, which recommends plants that the state Department of Agriculture should ban from sale and add to Pennsylvania’s official Controlled Plants List.
The Ag Department has added a dozen new plants to its Controlled Plants List in the last three years, including flowering pear trees, burning bushes, Japanese barberries, and four kinds of privets. The full list – as well as the department’s own roundup of emerging weed threats – is available on the Ag Department website.
Plants that made it onto the Massachusetts list aren’t just what most people call “weeds.” It includes some plants that gardeners still buy and purposely plant as ornamentals but that have the potential to spread out of control and cause harm.
Four of those rated a second-level alert in Pennsylvania: heavenly bamboo (Nandina domestica), a semi-evergreen broadleaf shrub; crape myrtle (Lagerstroemia indica), a small flowering tree; Aaron’s beard (Hypericum calycinum), a yellow-blooming spreading shrub, and bloodflower milkweed (Asclepias curassavica), a flowering perennial.
Japanese privet (Ligustrum japonicum) – another second-level Pennsylvania alert plant – is a broadleaf evergreen that’s planted in many Pennsylvania yards but is among the plants that the state Ag Department recently banned for sale.
Other plants on the Pennsylvania second-level alert list: white bladderflower (Araujia sericifera), a perennial vine; bellardia (Bellardia trixago), a reseeding annual; annual false-brome (Brachypodium distachyon), an annual grass; day jessamine (Cestrum diurnum), a hardy small tree; hairy fleabane (Conyza bonariensis), a reseeding annual/biennial; Indian rosewood (Delbergia sissoo), a perennial flower; Algerian ivy (Hedera canariensis), a perennial vine; vaseygrass (Paspalum urvillei), a perennial grass; African rue (Peganum harmala), a perennial flower; coffee senna (Senna occidentalis), an annual (and maybe perennial), red sesbania (Sesbania punicea), a perennial flower, and Spanish broom (Spartium junceum), a perennial flower.
These photos show Penn State researchers in action in the field in the effort to measure root depths without digging up plants.Penn State University/Creative Commons
Deeper-rooted plants on the horizon
A new root-measuring technique developed at Penn State University could speed the way to deeper-rooted plants that withstand drought conditions better.
Penn State researchers have figured out a way to scan and measure root depths without having to dig up plants.
The process, using X-ray fluorescence spectroscopy, took six years of research and involved the analysis of more than 2,000 soil core samples at four research sites across the country.
“We’ve known about the benefits of deeper rooting crops for a long time,” says Dr. Jonathan Lynch, a Penn State plant science professor and leader of the root-research team. “They are more drought tolerant and have an enhanced ability to take up nitrogen. But the problem has been how to measure root depth in the field. To breed deeper-rooted crops, you need to look at thousands of plants. Digging them up is expensive and time-consuming because some of those roots are down two meters or more. Everybody wants deep-rooted crops, but until now, we didn’t know how to get them.”
Deeper-rooted plants also store carbon in the soil more effectively, Lynch adds.
“Carbon in the atmosphere is a bad thing,” he says. “It causes global warming. Carbon in the soil is a good thing. It boosts fertility. The deeper carbon is put in the soil, the longer it stays in the soil... The U.S. Department of Energy estimates that just having deep-rooted crops in America alone could offset years of our total carbon emissions. That’s huge. Think about all the acres growing crops in America. If those roots grow just a little bit deeper, then we’re storing massive amounts of carbon deeper in the soil.”
Although Penn State’s work focused on corn roots, the non-dig, root-measuring technique can be used on other plants as well, potentially speeding the work of plant breeders trying to develop more drought-resistant landscape plants.
Trees' use of carbon dioxide varies by climate, new research shows.George Weigel
Trees don’t ‘breath’ as well in a warming climate
Another Penn State study found that trees do a poorer job of drawing carbon dioxide out of the atmosphere as the climate warms – especially when it’s warmer and drier as current climate forecasts project.
Max Lloyd, the Penn State assistant professor of geosciences who led the research, says the finding complicates the prevailing wisdom that planting more trees will greatly aid our heat-trapping carbon-dioxide problem.
“We found that trees in warmer, drier climates are essentially coughing instead of breathing,” says Lloyd. “They are sending CO2 right back into the atmosphere far more than trees in cooler, wetter conditions.”
In ideal photosynthesis, trees remove CO2 from the air and use it to produce growth. But in stressful conditions, Lloyd says, trees release some CO2 back into the atmosphere in a process called “photorespiration.”
By measuring photorespiration in sub-tropical climates, Lloyd says the threshold between ideal and stress seems to happen when average daytime temperatures exceed 68 degrees.
He says photorespiration can be twice as high in warmer climates as cooler ones, especially when the climates are dry as well as warm.
The findings are useful in models that help determine future carbon-dioxide levels and in deciding which strategies will be most effective in keeping a lid on them. Also, some tree species may be more effective in CO2 use than others at higher temperatures.
The Penn State research also developed a way to evaluate photorespiration in fossilized wood from millions of years ago, allowing a comparison spanning from the distant past into the future.
Bug feeding such as from these spongy moth caterpillars can do more than just cause leaf loss.John H. Ghent/USDA Forest Service
A new way that bad bugs hurt good ones
A study of trees eaten by spongy moth caterpillars showed for the first time how an invasive bug can harm native bugs by making their shared food resource more toxic.
Dr. Richard Lindroth led a team of researchers in a University of Wisconsin project that looked at what happened to native silk moth caterpillars after spongy moths (the bug formerly known as gypsy moths) defoliated an aspen forest near Madison, Wisc.
The study compared the situation to a similar forest of aspens just four miles away that the spongy moths didn’t touch.
Researchers found that when the aspens grew a second set of leaves by early July to replace the ones lost during the May-June spongy-moth attack, those leaves had levels of bug-defending and bug-toxic salicinoid compounds that were more than eight times higher than the first set.
Leaves in the non-attacked stand of aspens had the same lower levels of salicinoids as the first set of spongy-moth-attacked aspens.
The researchers then evaluated how silk moths fared in their summer feeding – in the defoliated forest area as well as when fed leaves from both the control and attacked trees.
“The high levels of defense compounds in the defoliated forest caused serious damage to the native silk moth caterpillars,” Lindroth writes in a post on The Conversation website. “Few caterpillars survived when fed leaves from the previously defoliated forest. Those that did survive had stunted growth.”
The research adds to the body of evidence showing how invasive species can harm native ecosystems and why it’s important to control them – or better yet, prevent them from getting a leg up.
A new study of bumble bees found that these buzzing feeders act a bit like human consumers.George Weigel
Bees are ‘irrational shoppers’
One of the more curious findings comes from the University of Tennessee, where researchers looked at which flowers bumblebees were more likely to visit for a snack than others.
The conclusion was that bumblebees are a lot like human shoppers – highly influenced by perceptions.
“You’d think bees would always pick the flowers with the most accessible, highest-quality nectar and pollen,” writes lead researcher and University of Tennessee assistant professor of ecology Claire Therese Hemingway. “But they don’t. Instead, just like human grocery shoppers, their decisions about which flowers to visit depend on their recent experience with similar flowers and what other flowers are available.”
In one experiment, Hemingway’s team trained bumblebees to associate blue flowers with high-quality nectar and yellow flowers with medium-quality nectar. When those bees later were offered a choice of blue or yellow flowers, they were more willing than otherwise to accept the medium-quality nectar in the yellow flowers.
“Their expectations mattered,” says Hemingway.
In a second experiment, the team gave the bees a choice between two sugar solutions – one high in sugar but slower to refill and one quick to refill but with less sugar. Their preference was similar.
However, when a third solution was added that was even lower in sugar and slower to refill, the new low-reward choice made the medium-sugar choice more attractive.
Hemingway says this is similar to how humans expect that an expensive wine with a French label is going to be better than a cheap generic wine or how a human will react to a $5 winning lottery ticket after winning a $1 one vs. after winning a $10 one.
“Research shows bumblebees and humans share many of these behaviors,” Hemingway says.
She adds that the findings may be useful to farmers and gardeners by helping them decide which plants to plant near one another to maximize bee visits to target species.