Plants may tell us when they're in trouble.Thirsty tomato and tobacco plants make clicking sounds,researchers have found.The sounds are ultrasonic (超声波的),meaning they are too high-pitched for human ears to hear.But when the sounds are transformed to lower pitches,they sound like popping bubbles (爆破的泡泡).Plants also make clicks when their stems (茎) are cut.
"It's not like the plants are screaming," says Lilach Hadany,an evolutionary biologist working at Tel Aviv University in Israel."Plants may not mean to make these noises.We've shown only that plants create informative sounds."
Hadany and her colleagues first heard the clicks when they set microphones next to plants on tables in a lab.The microphones caught some noises.But the researchers needed to make sure that the clicking was coming from the plants.So,the scientists placed plants inside soundproof boxes in the basement,far from the noise of the lab.There,microphones picked up ultrasonic pops from thirsty tomato plants.Though it was outside humans' hearing range,the clicking made by plants was about as loud as a normal conversation.
Cut tomato plants and dry or cut tobacco plants clicked,too.But plants that had enough water or hadn't been cut stayed mostly quiet.Wheat,corn and grapevines also made sounds when stressed out.
The researchers don't yet know why plants click.Bubbles forming and then popping inside plant tissues that transport water might make the noises.But however they happen,pops from crops could help farmers,the researchers suggest.Microphones,for example,could monitor fields or greenhouses to detect when plants need to be irrigated (灌溉).
Hadany wonders whether other plants and insects already tune into plant pops.Other studies have suggested that plants respond to sounds.And animals from pests (害虫),moths to mice can hear in the range of the ultrasonic clicks.Sounds made by plants could be heard from around five meters away.Hadany's team is now studying what the living things near the plants will do after hearing the sounds.
