Recent summer temperatures in parts of Australia were high enough to melt asphalt. As global warming speeds up the heat and climatic events increase, many plants may be unable to cope. But at least one species of eucalyptus tree can resist extreme heat by continuing to “sweat” when other essential processes stop, a new study finds.

As plants change sunlight into food, or photosynthesize (光合作用), they absorb carbon dioxide through pores on their leaves. These pores also release water via transpiration(蒸腾), which circulates nutrients through the plant and helps cool it by evaporation(蒸发). But exceptionally high temperatures are known to greatly reduce photosynthesis—and most existing plant models suggest this should also decrease transpiration, leaving trees in danger of fatally overheating. Because it is difficult for scientists to control and vary trees’ conditions in their natural environment, little is known about how individual species handle this situation.

Ecologist John Drake of the S.U.N.Y. College of Environmental Science and Forestry and his colleagues grew a dozen Parramatta red gum (Eucalyptus parramattensis) trees in large, climate-controlled plastic pods that separated the trees from the surrounding forest for a year in Richmond, Australia. Six of the trees were grown at surrounding air temperatures and six at temperatures three degrees Celsius higher. The researchers withheld (扣留) water from the surface soil of all 12 trees for a month to imitate a mild dry spell, then induced a four-day “extreme” heat wave: They raised the maximum temperatures in half of the pods（three with surrounding temperatures and three of the warmer ones）— to 44 degrees ℃.

Photosynthesis ground to a near halt in the trees facing the artificial heat wave. But to the researchers’ surprise, these trees continued to transpire at close-to-normal levels, effectively cooling themselves and their surroundings. The trees grown in warmer conditions coped just as well as the others, and photosynthesis rates bounced back to normal after the heat wave passed, Drake and his colleagues reported online in Global Change Biology.

The researchers think the Parramatta red gums were able to effectively sweat — even without photosynthesis — because they are particularly good at tapping into water deep in the soil. But if a heat wave and a severe drought (干旱) were to hit at the same time and the groundwater was exhausted, the trees may not be so lucky, Drake says.

Other scientists call the finding encouraging. “It’s definitely good news,” says Trevor Keenan, an ecologist at Lawrence Berkeley National Laboratory, who was not part of the study. “It would be very interesting to know how this translates to other species,” he adds. Drake hopes to conduct similar experiments with trees common in North America.

5-second rule: what’s the truth?

Almost everyone has dropped some food on the floor and still wanted to eat it. If someone saw you drop it, he or she might have shouted, ＂5-second rule!＂This so-called rule says food is OK to eat if you pick it up in five seconds or less. But is that true?

Professor Anthony Hilton from Ashton University, UK, tested the rule with his students. They found that food dropped for five seconds is less likely to contain bacteria(细菌) than if it sits there for longer.

For the study, Hilton and his students tested a lot of food—bread, pasta, cookies and candy—to see how much bacteria they had when they made contact with the floor. They allowed the food to lie on various types of flooring-carpet, laminate(复合地板), and tile (瓷砖) for three seconds to 30 seconds.

Not surprisingly, the longer the food was on the floor, the more bacteria it had. And the type of floor where the dropped food landed had an effect. Bacteria are least likely to transfer from carpet, while they’re most likely to transfer from laminate or tiled surfaces after more than five seconds.

The study also found that the wetter the food, the more likely it was to pick up bacteria. Although most people are happy to follow the 5-second rule, eating food dropped on the floor still carried an infection(感染) risk. ＂It very much depends on which bacteria are on the floor at the time,＂ Hilton told Forbes.

What would the world be if there were no hunger? It’s a question that the late ecologist Donella Meadows would ask her students at Dartmouth College back in the 1970s. She set out to create a global movement. The result—an approach known as systems thinking—is now seen as essential in meeting big global challenges.

Systems thinking is crucial to achieving targets such as zero hunger and better nutrition because it requires considering the way in which food is produced, processed, delivered and consumed, and looking at how those things relate with human health, the environment, economics and society. According to systems thinking, changing the food system—or any other network—requires three things to happen. First, researchers need to identify all the players in that system; second, they must work out how they relate to each other; and third, they need to understand and quantify the impact of those relationships on each other and on those outside the system.

Take nutrition for example. The United Nations Food and Agriculture Organization tracked 150 biochemicals in food and various databases, which revealed the relationships between calories, sugar, fat, vitamins and the occurrence of common diseases. But using machine learning and artificial intelligence, network scientists propose that human diets consist of at least 26,000 biochemicals and that the vast majority are not known. This shows that we have some way to travel before achieving the first objective of systems thinking—which, in this example, is to identify more constituent parts of the nutrition system.

A systems approach to creating change is also built on the assumption that everyone in the system has equal power and status. But the food system is not an equal one. There have been calls for a World Food and Nutrition Organization, so that legally binding policies can be applied to all its members. Another way to address power imbalances is for more universities to do what Meadows did and teach students how to think using a systems approach.

A team of researchers has done just that, through the Interdisciplinary Food Systems Teaching and Learning program. Students from disciplines including agriculture, ecology and economics learn together by drawing on their collective expertise in tackling real-world problems, such as how to reduce food waste. Since its launch in 2015, the program has trained more than 1,500 students from 45 university departments.

More researchers, policymakers and representatives from the food industry must learn to look beyond their direct lines of responsibility and embrace a systems approach, as the editors of Nature Food advocate in their launch editorial. Meadows knew that visions alone don’t produce results, but concluded that “we’ll never produce results that we can’t envision”.