Plants picky over human contact

By Vianne Fung

Botanists found that handling plants in the field may have serious consequences for the plants.

University of Alberta professor James Cahill has discovered that touching plants may alter the chances insects will feed upon the plants’ leaves.

“This will have potential dramatic implications for field biologists. We will have to be more aware of this when we walk in the field to do research,” explained Cahill.

Cahill, along with Jeffrey Casteilli and Brenda Casper from the University of Pennsylvania, published an article titled “The Herbivory Uncertainty Principle,” in the February issue of Ecology.

The study began while Cahill was completing his PhD at the University of Pennsylvania as he and his colleagues examined plants in an abandoned hayfield. They noticed that plants marked for a competition study were experiencing high rates of attack by insects.

“We wondered whether us being out there was somehow influencing the survival of these plants,” Cahill explained.

To test their theory, they marked 605 plants of six common species in the valley. Half the visited plants were regularly stroked from base to tip, while the team was careful not to damage the plants. After an eight-week period, Cahill and his colleagues compared the two groups by noting the survival of each plant and measured the extent of leaf damage.

Three of the six species showed an observable response. The Albertan native Indian Hemp suffered fatal leaf damage while the Sulphur Cinquefoil and a species known as “butter and eggs” seemed to benefit from the visits.

“It was interesting that there was a response and it was in two contrasting directions,” said Cahill. “It shows that we weren’t damaging the plants and simply crushing them.”

According to Cahill, these findings may be explained by several theories.

“In response to touching or attack, many plants release chemicals that may attract both the insects that feed on them and those that feed on the predators,” Cahill explained. “We didn’t think there would be a response. It’s important for us to find out whether this is a genuine phenomenon–but field biologists can no longer assume that their activities in the field do not alter the biology of the organisms studied.”


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