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18 | NewScientist | 24 November 2012 PLANTS, it turns out, are showing signs of living recklessly. About 70 per cent of forest plant species seem to live within a slim safety margin of survival in the face of drought and changing rainfall patterns. What’s more, trees and flowering plants in wetter forests not often considered to be at risk of drought are endangered by their profligacy with water. Biologist Steven Jansen, at the University of Ulm, Germany, and colleagues analysed existing data on the water transportation systems of 226 plant species from 81 forests globally (Nature, DOI: 10.1038/nature11688). Jansen says drought stress causes bubbles of gas to be brought into plants’ water transport tubes, which blocks water from reaching leaves and in turn halts the food-creating The insect with mammal-like ears ALL the better to hear you with, my dear. A species of bush cricket in the South American rainforest has ears divided into three parts, similar to those of mammals. Fernando Montealegre-Z at the University of Lincoln, UK, and colleagues were studying the eardrum-like tympanal membrane in the foreleg of Copiphora gorgonensis, when they unexpectedly burst a vessel behind the membrane. It was filled with high-pressure fluid that was not part of the predatory insect’s circulatory system, leading them to conclude that the vessel detects sound in the same way as the cochlea in a mammal’s ear (Science, doi.org/jrt). In most insects, sound is transmitted directly to sensors behind the tympanal membrane. The bush cricket’s unusual ears can hear what to us would be ultrasonic frequencies, probably allowing it to tell mates from foes. Soaring emissions promise to supersize sweet potatoes RISING levels of carbon dioxide in the atmosphere may have a silver lining: doubling the size of the sweet potato, the fifth most important food crop in the developing world. Most studies of the effects of higher atmospheric CO 2 on crops have shown rising yields of rice, wheat and soy. The hardy sweet potato is increasingly becoming a staple in Africa and Asia, producing “more edible energy per hectare per day than wheat, rice or cassava”, according to research group the International Potato Center. Hope Jahren at the University of Hawaii at Manao and colleagues grew the plants at four CO 2 concentrations: KEYSTONEUSA-ZUMA/REX IN BRIEF Reckless forest plants living on the edge process of photosynthesis. In wetter forests, plants have a greater access to water so have wider water tubes. As well as increasing water intake, this also ups the intake of gas bubbles and hence the risk of blockages. Rainforests and drier forests are equally at risk, says Jansen. The study shows that “all plants seem to be living on the edge”, says Yadvinder Malhi, an ecosystems scientist at the University of Oxford. the current level of 390 parts per million, as well as 760, 1140 and 1520 ppm. The Intergovernmental Panel on Climate Change predicts that atmospheric CO 2 levels will be between 500 and 1000 ppm by the year 2100. For the least extreme scenario at 760 ppm, the team found the tubers grew up to 96 per cent larger. The team is now testing their nutrient content. “Are these sweet potatoes any more nutritious,” asks team member Ben Czeck, “or do you have to eat twice as many to get the nutrients needed?” Crucially, previous studies revealed the protein content in wheat, rice, barley and potatoes dropped by 15 per cent when grown under CO 2 levels double those of today. Czeck will present the work in December at the American Geophysical Union meeting in San Francisco. LOOKING for the biggest pie in the solar system? Make a stop at Mercury, which boasts the only known craters with wrinkled crusts and cracked fillings. Spotted by NASA’s Messenger spacecraft, the formations were created early in the planet’s history, when volcanic outbursts flooded impact craters. As the lava cooled, material above the rims wrinkled, making the outlines visible (Geology, doi.org/jrz). Inside, cooling lava contracted, but as some was attached to the crater edges, it formed pie-like cracks, says Thomas Watters of the Smithsonian Institution in Washington DC. Volcanic flooding on Mars and the moon happened in slow, thin gushes that probably could not have made such “pies”. NASA serves up giant pie in the sky
