有些树在高温天气下 会流汗

Some Trees Beat Heat with Sweat

有些树在高温天气下 会流汗

Here's a short piece from the May 2018 issue of the magazine, in the section we call Advances: Dispatches from the Frontiers of Science, Technology and Medicine:


Sweaty Trees, by Yasemin Saplakoglu


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

澳大利亚部分地区最近的夏季气温高到足以融化沥青。随着全球变暖所导致的日益加剧的高温和气候问题, 许多植物可能无法应对。但一项新研究发现, 至少有一种桉树能经受住酷热的考验,因为当其他必要的过程逐渐减弱时,它们会不停地“出汗”。

As plants convert sunlight into food, or photosynthesize, they absorb carbon dioxide through pores on their leaves. These pores also release water via transpiration, which circulates nutrients through the plant and helps cool it by evaporation. 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 isolated the trees from the surrounding forest for a year in Richmond, Australia. Six of the trees were grown at ambient air temperatures and six at temperatures three degrees Celsius higher. The researchers withheld water from the surface soil of all 12 trees for a month to simulate a mild dry spell, then induced a four-day "extreme" heat wave: They raised the maximum temperatures in half of the pods (three with ambient temperatures and three of the warmer ones) - to 44 degrees C.

纽约州立大学环境科学与林业科学学院的生态学家约翰. 德雷克和他的同事们在澳大利亚里士满,在一打大型的、温度可控的塑料隔离舱内分别种植了帕拉玛塔赤桉树,隔离舱可将树木与周围的环境隔离开,测试时间长达一年。其中六棵树在与周围空气温度一致的环境下生长,另外六棵树在比周围环境温度高3度的环境下生长。研究人员让所有12棵树的表层土壤断水一个月来模拟一个轻度干旱的状态,然后引起了连续四天的“极端”热浪:科学家们将一半塑料仓的最高温度升高(其中三个与周围温度一样、另三个要高三度的塑料仓)至44℃。

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 these findings in Journal 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 were to hit at the same time and the groundwater was depleted, 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.