'Probiotics' for plants boost detox abilities; untreated plants overdose and die

The Doty lab conducts work to see how plants treated with naturally occurring endophytes might handle soils contaminated with a variety of pollutants. Graduate student Robert Tournay, for example, is interested in how the plants handle arsenic. Credit: M Levin/U of Washington

Scientists using a microbe that occurs naturally in eastern cottonwood trees have boosted the ability of two other plants -- willow and lawn grass -- to withstand the withering effects of the nasty industrial pollutant phenanthrene and take up 25 to 40 percent more of the pollutant than untreated plants.

The approach could avoid the regulatory hurdles imposed on transgenic plants -- plants with genes inserted from or exchanged with other plant or animal species -- that have shown promise in phytoremediation, the process of using plants to remove toxins from contaminated sites, according to Sharon Doty, associate professor of environmental and forestry sciences and corresponding author on a paper about the new work in Environmental Science & Technology.

"Our approach is much like when humans take probiotic pills or eat yogurt with probiotics to supplement the 'good' microbes in their guts," she said.

The microbe from the cottonwood was encouraged to colonize the roots of willows simply by dipping rooted and trimmed cuttings in solutions with the microbe. Grasses were treated with microbes in solution as seeds sprouted in soil. Once integrated into the plants, the microbe supplemented their own microbial defenses.

Microbes that take up residence in the inner tissue of plants and don't cause negative symptoms are called endophytes. In nature, endophytes have a welcomed, symbiotic relationship with plants. In polluted soil, for instance, if the right endophytes are present they consume toxins coming up through plant roots. The endophytes get fed and the plant gets help neutralizing pollutants that could kill it.

That's been one challenge of phytoremediation: plants removing pollutants can, all too quickly, succumb to the toxins.

"When the endophyte in these experiments was given to willow and grasses, it reduced the phytotoxic effects of phenanthrene compared to the control plants that did not receive the endophyte and died," said lead author Zareen Khan, a UW research scientist in environmental and forest sciences.

Phenanthrene is carcinogenic, on the Environmental Protection Agency's priority pollutants list and belongs to a class of polycyclic aromatic hydrocarbons that get deposited into the environment via fossil fuel combustion, waste incineration or as byproducts of industrial processes. Soils that become contaminated can be capped with layers of uncontaminated soil or dug up and removed for cleaning at soil remediation facilities or storage at waste disposal facilities.

In their search, UW researchers tested six different endophytes from cottonwood and willow varieties and found one -- lab name PD1 -- from the eastern cottonwood to be superior at breaking down phenanthrene.

They introduced this endophyte into willow cuttings and lawn grass. Willows were chosen because some varieties have already proven adept at removing toxins and the shrubs have extensive root systems, take up a lot of water and grow rapidly. Lawn grass was included because it also grows fast and could be useful in parks and open-space areas.

In lab experiments, the willow cuttings with added endophyte protection continued to grow, kept their leaves and had denser root systems. Untreated plants wilted, lost leaves and their roots turned brown. When soils were analyzed, the treated willows took up 65 percent of the phenanthrene compared with untreated plants that removed 40 percent, an improvement of 25 percent.

Grass seed planted in contaminated soils and watered with solutions containing the PD1 endophyte germinated five days quicker, grew taller and had 100 more tillers, or new offshoots, after 13 days. Treated grass removed 50 percent of the phenanthrene from the soil, compared with untreated grass that removed 10 percent, an improvement of 40 percent.

In phytoremediation, plants that take up pollutants but don't degrade them have to be removed and treated as hazardous waste or otherwise disposed of safely. The willows treated in the UW experiment appear to have degraded some 90 percent of the phenanthrene to harmless components. The researchers said they'd like to determine if that promising finding holds up in mass-balance studies and want to examine the possible effects on bugs or animals that might bite the plants processing the toxins and other environmental considerations. Interestingly, other studies have shown that bugs can smell similar semi-volatile pollutants and avoid eating the plants containing them, Doty said.

The work was funded by a Small Business Innovation Research grant from the National Institute of Environmental Health Sciences and by funds provided through the Byron and Alice Lockwood Endowed Professorship that Doty holds. The other four co-authors on the paper were undergraduate volunteers: David Roman and Trent Kintz have since graduated while May delas Alas and Raymond Yap are still working on their bachelor's degrees.
Just down the road from UW is Seattle's Gas Works Park, a site Doty thinks is a prime candidate for the approach her lab reported. Contaminants in the soil, including phenanthrene, are from a now-dismantled gasification plant. Soils have been covered with uncontaminated soil.

"The idea of leaving a known carcinogen in a public place is not right," she said. "What about problems of erosion? We should do what we can to remove it. We spend so much money treating cancer, I'd like us to take steps to prevent it instead."

Source: University of Washington

If trees could talk: Forest research network reveals global change effects

In addition to identifying, mapping, measuring and monitoring trees in the CTFS-ForestGEO study plots, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why. Credit: Beth King, STRI

Permafrost thaw drives forest loss in Canada, while drought has killed trees in Panama, southern India and Borneo. In the U.S., in Virginia, over-abundant deer eat trees before they reach maturity, while nitrogen pollution has changed soil chemistry in Canada and Panama. Continents apart, these changes have all been documented by the Smithsonian-led Center for Tropical Forest Science-Forest Global Earth Observatory, CTFS-ForestGEO, which released a new report revealing how forests are changing worldwide.

"With 107 collaborators we've published a major overview of what 59 forests in 24 countries, where we monitor nearly 6 million trees teach us about forest responses to global change," said Kristina Anderson-Teixeira, first author of the report and CTFS-ForestGEO and ecosystem ecologist based at the Smithsonian Conservation Biology Institute.

Many of the changes occurring in forests worldwide are attributable to human impacts on climate, atmospheric chemistry, land use and animal populations that are so pervasive as to warrant classification of a new geologic period in Earth's history -- the Anthropocene, the Age of Humans.

Measuring and understanding the effects of all these changes -- collectively termed "global change" -- are easier said than done. Some of the best information about these global-scale changes comes from CTFS-ForestGEO, the only network of standardized forest-monitoring sites that span the globe.

Since the censuses began at the first site on Barro Colorado Island in Panama in 1981, atmospheric carbon dioxide has increased by 16 percent. The forest sites in the network have warmed by an average of over 1 degree F (0.6 degree C) and experienced up to 30 percent changes in precipitation. Landscapes around protected sites experience deforestation.
The plot network now includes forests from Brazil to northern Canada, from Gabon to England and from Papua New Guinea to China.

In addition to identifying, mapping, measuring and monitoring trees, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why.

Climate change scenarios predict that most of these sites will face warmer and often drier conditions in the future -- some experiencing novel climates with no modern analogs. Forests are changing more rapidly than expected by chance alone, and shifts in species composition have been associated with environmental change. Biomass increased at many tropical sites across the network.

"It is incredibly rewarding to work with a team of forest scientists from 78 research institutions around the world, including four Smithsonian units" Anderson-Teixeira said. "CTFS-ForestGEO is a pioneer in the kind of collaborative effort it takes to understand how forests worldwide are changing."

"We look forward to using the CTFS-ForestGEO network to continue to understand how and why forests respond to change, and what this means for the climate, biodiversity conservation and human well-being," said Stuart Davies, network director.

Source: Smithsonian Tropical Research Institute