Message Undeliverable

Plants have their own way of communicating: they send chemical signals to alert each other when they’ve been nibbled by herbivores. But according to a study in Ecology Letters, ozone pollution can hinder the delivery of these messages.

An attacked plant may release volatile organic compounds (VOCs), chemicals which are detected by its neighbors. The “receiver” plants then respond by mounting defenses against herbivores. For example, they may secrete extra nectar to attract an herbivore’s predators.

Researchers decided to find out whether rising ozone levels would impede this communication. They set up a row of lima bean plants (Phaseolus lunatus) infested with two-spotted spider mites (Tetranychus urticae). Then they placed one row of “receiver” plants 20 centimeters away and another row 70 centimeters away.

At normal ozone levels, both rows of “receiver” plants picked up the signal from infested plants and consequently increased their nectar production. But when ozone levels rose to 80 parts per billion, the farthest row of plants no longer responded. The VOCs may have been degraded before they reached the back row, the authors say.

Complicating the picture, the researchers found, higher ozone levels of 120 to160 parts per billion actually provoked nectar secretion directly. This reaction could be part of a general stress response, they say. ❧

—Roberta Kwok

Blande, J.D., J.K. Holopainen and T. Li. 2010. Air pollution impedes plant-to-plant communication by volatiles. Ecology Letters doi:10.1111/j.1461–0248.2010.01510.x.

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