Although it has been shown in recent years that plants can see, hear and smell, they are still usually thought of as silent. But now, for the first time, they have been recorded making ultrasonic (超声的) cries when stressed, which researchers say could open up a new field of precision agriculture where farmers listen for water-starved crops.
Itzhak Khait and his colleagues at Tel Aviv University in Israel found that tomato and tobacco plants made cries at frequencies humans cannot hear when stressed by not having enough water or when their stem is cut.
Microphones placed 10 centimetres from the plants picked up sounds in the ultrasonic range of 20 to 100 kilohertz, which the team says insects and some mammals would be able to hear and respond to from as far as 5 metres away. A moth may decide against laying eggs on a plant that sounds water-stressed, the researchers suggest. Plants could even hear that other plants are short of water and react accordingly, they speculate (推断).
On average, drought-stressed tomato plants made 35 sounds an hour, while tobacco plants made 11. When plant stems were cut, tomato plants made an average of 25 sounds in the following hour, and tobacco plants 15. Unstressed plants produced fewer than one sound per hour, on average.
Enabling farmers to listen for water-stressed plants could "open a new direction in the field of precision agriculture", the researchers suggest. They add that such an ability will be increasingly important as climate change exposes more areas to drought.
"The suggestion that the sounds that drought-stressed plants make could be used in precision agriculture seems feasible (可行的) if it is not too costly to set up the recording in a field situation," says Anne Visscher at the royal Botanic Gardens, Kew, in the UK.
She warns that the results can't yet be broadened out to other stresses, such as salt or temperature, because these may not cause sounds. Besides, there have been no experiments to show whether moths or any other animal can hear and respond to the sounds the plants make, so that idea is still based on guesses for now, she says.
