A variety of corn from Oaxaca, Mexico, has aerial roots that harbor nitrogen-fixing bacteria, allowing the corn to suck nitrogen straight from the air. Christopher Intagliata reports. 

墨西哥瓦哈卡(Oaxaca, Mexico)的许多种玉米都有气生根，它们可以让固氮细菌附着于上，这样玉米就可以直接从空气中吸收氮元素了。克里斯托弗·因塔利亚塔报道。

撰文播音：克里斯托弗·因塔利亚塔（Christopher Intagliata）

翻译：邱燕宁

审校：张清越

Plants need three things to grow: air, water and nutrients. Farmers usually take care of the last bit by fertilizing their fields. But now scientists have found a type of corn that seems to thrive on air and water alone. 

植物需要三样东西才能生长:空气、水和营养。为了保证最后一点，农民通常会给他们的田地施肥。但现在科学家们发现了一种玉米，它似乎只靠空气和水就能茁壮成长。

"This has been sort of the holy grail, you know, if only I could grow corn and not put 200 pounds of nitrogen on it." Allen Van Deynze is a plant breeder at the University of California, Davis, and part of a team that analyzed this one corn’s unusual ability. 

“如果我不用放200磅氮就能让玉米茁壮生长，那简直太好了。”Allen Van Deynze说。他是加州大学戴维斯分校的一名植物育种专家，也是一个研究小组的成员，该小组分析了这种玉米非同寻常的能力。

The corn variety hails from Oaxaca, Mexico, where it typically grows in nitrogen-poor soils. Nitrogen is needed for proteins, DNA and the chlorophyll that let plants perform photosynthesis. But the Oaxacan corn does well despite the bad soil, and with little or no fertilization. 

这种玉米来自墨西哥瓦哈卡，主要生长在氮贫瘠的土壤中。氮是蛋白质、DNA和让植物进行光合作用的叶绿素所必需的。虽然土壤贫瘠，而且几乎没有施肥，但是瓦哈卡的玉米还是长得很好。

The plants pull off this trick via thick, red, aerial roots that protrude from its stem—above the ground—that ooze out a clear goo packed with sugars. That slime is the perfect habitat for nitrogen-fixing bacteria: a sugar-rich, oxygen-poor environment where the microbes transform nitrogen gas into a soluble form the corn plant can use. It’s an above-ground version of the nitrogen-fixation you might usually think of as happening in the underground roots of legumes, like peas and beans. 

植物通过从茎上伸出来的又厚又红的气生根系来解决这一难题。这种气生根能够渗出含糖的黏液，而这种黏液是固氮细菌的完美栖息地:这是一种含糖分高、含氧量低的环境，微生物可以在这里将氮气转化为玉米植株可以利用的可溶性物质。通常我们认为固氮过程发生在豆类的地下根部，而这是一种地面上的固氮方式。

The researchers demonstrated the corn plants’ talent by exposing them to labeled isotopes of nitrogen. And they were able to track the movement of the distinctly identifiable nitrogen atoms from the air, to the root, and into the plant. This pathway allows the corn to obtain up to 80 percent of its nitrogen straight out of the air. The details are in the journal PLOS Biology. [Allen Van Deynze et al., Nitrogen fixation in a landrace of maize is supported by a mucilage-associated diazotrophic microbiota]

研究人员通过将玉米暴露在标记过的氮同位素中来展示和研究它们的这种能力。他们能够追踪到氮原子从空气、到根部、到植物的运动。玉米通过这一途径直接从空气中获得80%的氮。详情刊登在《PLOS Biology》杂志上。

Van Deynze says early plant breeders may have inadvertently got rid of corn’s nitrogen-fixing proficiency long ago. "When early man made some selections for bigger ears, higher yield, perhaps they lost this ability along the way. And we have the opportunity perhaps to bring it back."

Van Deynze说，早期的植物育种家可能很久以前就在无意中抛弃了玉米的固氮能力。“早期人类在选择大抽穗、高产量的过程中，它们可能使玉米失去了这种能力。我们或许有机会把它带回来。”