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After decades of seeing plants as passive recipients of fate, scientists have found them capable of behaviors once thought unique to animals. Some plants even appear to be social, favoring family while pushing strangers from the neighborhood.
Research into plant sociality is still young, with many questions unanswered. But it may change how people conceive of the floral world, and provide new ways of raising productivity on Earth's maxed-out farmlands.
"When I was in school, researchers assumed that some plants were better or worse than others at getting resources, but they were blind to the whole social situation," said Susan Dudley, a McMaster University biologist. "I went looking for it, and to my shock, found it. And we've found more of it since."
In a paper published in the November American Journal of Botany, Dudley describes how Impatiens pallida, a common flowering plant, devotes less energy than usual to growing roots when surrounded by relatives. In the presence of genetically unrelated Impatiens, individuals grow their roots as fast as they can.
Acknowledging relatives in this way is an example of kin recognition. It's common in the animal world, and is a precursor to kin selection, in which animals help their familial group, not just themselves. Dudley thinks plants have kin selection, too. It's a controversial idea, but that it's even being debated shows how far research into plant sociality has come.
When Dudley was in school in the 1980s, the very idea of plant sociality was practically taboo among scientists. It had burst into popular consciousness a decade earlier with the publication of The Secret Life of Plants, a New Age classic which also discussed orgones and dowsing. Later studies on "talking trees" went unreplicated, and the idea fell into disrepute.
But even if full-blown sentience was a silly idea, research on plant communication gathered. Much of it described how plants defended themselves, producing toxins and concentrating resources on their immune systems when unrelated neighboring plants were eaten. That clearly involved some sort of chemical signaling. Further studies conclusively showed plants were able to recognize themselves. Whether plants might respond to their relatives became a legitimate and intriguing question.
The answer isn't only of concern to people with imaginations stirred by thoughts of chatting flora. It could provide a whole new perspective on plant behavior and evolution. By providing insights that improve agricultural productivity, studies of kin recognition could literally bear fruit.
"We know that in the animal world, kin recognition and selection plays a very important role for family structure, altruistic behavior and those kinds of things," said Hans de Kroon, a plant ecologist at Radboud University in the Netherlands. "It's so prominent in the animal literature. Once we start to discover that plants can recognize their kin, there's a whole set of hypotheses we can apply to studying plants, that nobody ever thought to."
The field's landmark paper came from Dudley's laboratory in 2007, when she showed how American searocket plants accelerated their root growth when placed in pots of strangers, but slowed it down when potted with siblings. Were they animals, they'd be described as sharing water and food.
In a Communicative and Integrative BiologyArabidopsis thalianaproved to be in the roots - and just as Dudley had seen, growth patterns varied according to whether secretions came from genetically unrelated plants, or family. paper published in October, University of Delaware biologists Harsh Bais and Meredith Biedrzycki tried to isolate the means of recognition by exposing seedlings, each in its own pot, to root secretions from other Arabidopsis plants. The signal indeed
Intriguingly, the plants in Dudley's latest study were potted separately and unexposed to each others' secretions, suggesting that their leaves emit chemical signals, as well as their roots. That's supported by the research of University of California, Davis ecologist Richard Karban, who in a June Ecology Lettersboosts its immune system when exposed to the damaged cuttings of a related plant [pdf]. It seems to hear warnings from its kin. study showed that sagebrush
More studies are needed to show exactly what sort of benefits are provided by these signaling and response systems. De Kroon said kin recognition doesn't necessarily mean kin selection: maybe the plants are communicating, but it doesn't do them much good in practice.
One of Dudley's students, Amanda File, is now studying whether some trees favor their own progeny, which might grow best near their parents. Dudley and graduate student Guillermo Murphy, a co-author of the American Journal of Botany paper, are looking for for kin selection in invasive plants.
"We're testing the hypothesis that invasive plants evolve greater altruism within their populations, allowing them to be better invaders of their new habitats," said Dudley.
For plants used in agriculture, Dudley recommends kin recognition studies to see whether certain arrangements of relatives and strangers would be especially productive. De Kroon is looking at multi-species mixes. Karban hopes to use communication insights to engineer natural defense systems against pests.
"Maybe we thought before that only humans could do certain things, or vertebrates, or animals," said Karban. "Plants are capable of much more sophisticated behavior than we assumed."
几十年以来，科学家一直把植物看成是被动接受命运安排的生物，但是日前科学家发现植物也有一些主动行为，而在此之前科学家一直以为那些只是动物特有的行为�？蒲Ъ颐巧踔粱狗⑾郑颖砻婵从行┲参锖孟窕褂猩缃换疃�，热爱自己的家族，以及会排斥附近出现的陌生"人".
目前，植物社交行为的研究才刚起步，还有很多问题尚未解决。不过，这项研究有可能改变人们对植物世界的看法，同时还有望提出新方法以解决目前地球上农田严重超支、农产品产量难以提高的问题。
麦克马斯特大学的生物学家苏珊 达德利说："我上学那会儿，研究断定植物植株吸收养分的能力是有差别的，有些强有些弱。但是当时他们却没有发现整个植物社交环境的存在。后来我开始研究这个领域，让我震惊的是，我发现了植物存在社交环境！到目前为止，在这一领域我们又有了更多研究成果。"
《美国植物学期刊》11月份那一期上发表了Dudley的一篇文章，文中Dudley描绘了一种名为淡紫凤仙花的普通开花植物，这种植物如果和亲属植株长在一起，根部生长就不如以往狂盛。但是，一旦周围有非亲属基因的凤仙花植株存在，它们的根就使劲长。
这种承认亲属存在的情况也属于亲属识别的例子。动物不仅保护自身也会�；ぷ约旱募易澹庑┫窒笤诙锸澜缋锸撬究占叩�，而且也是动物进行亲属选择的表现。Dudley认为植物同样会进行亲属选择。该观点目前还存在争议，不过人们对这一观点的争论正好可以反映出植物社交研究现已走到了哪一步。
上世纪80年代Dudley还在读书的那个时候，植物社交这个观点在科学界简直是个忌讳。但是十年前"植物的秘密生活"一文的发表，让全社会开始关注这个事情，这篇同时探讨了orgones和dowsing的文章可谓是一篇新的时代经典之作。但是，之后关于"会说话的树"的研究却没有得到人们的跟风，至此这个观点就开始不受重视了。
全民跟风虽然不是好事，但是至少植物交流的研究慢慢多起来了。绝大多数的此类研究写的都是植物在自己附近的非亲属植株被吃掉后是如何反应的，包括它们怎么�；ぷ约�、怎么制造毒液、怎么在免疫系统储备资源等等。很明显，这里涉及了一些化学方面的信号。最后，进一步研究又表明植物能认出它们自己那一伙的植株。所以，亲属植株之间可能会有反应是合乎情理的，但是它本身又是个相当复杂的问题。
对该问题给出解答并不仅仅是因为关心人民，怕聊天植物引的他们胡思乱想，还因为它能为我们理解植物行为，了解植物进化提供了一个全新的视角。亲属识别研究为提高农作物产量提供了不少想法，所以这项研究的确有可能结出丰硕的成果。
荷兰Radboud大学的植物生态学家Hans de Kroon说："我们知道在动物世界里，亲属识别和亲属选择在动物的家族结构、利他行为及其他各方面都发挥着至关重要的作用。同时，在动物文学作品中的表现也非常明显。一旦我们发现植物也能识别亲人，那么就将有一整套的假设可以用到植物研究中，而这是我们之前从未想到的。"
2007年，这一领域具有里程碑意义的文章从Dudley的实验室里诞生了。Dudley在实验室里发现American searocket这种植物如果跟陌生植株同盆种植，根系生长就会加快，相反的，如果和兄弟植株种在一起就会减慢。假如它们是动物，那就表现为共同分享水和食物。
到底这些化学信号和反应系统给植物提供什么好处呢，这还有待更多研究证实。De Kroon说亲属识别并不完全等同于亲属选择，可能植株之间存在交流，但是这并不能给它们带来实际的好处。
Dudley的学生Amanda File发现离母株最近的幼苗生长最好，因此他现在正在研究一些树种看它们是否真的自己关心下一代。目前，Dudley正和自己的研究生Guillermo Murphy--《美国植物学期刊》的合着者，研究入侵植物中的亲属选择情况。
Dudley说："目前我们正在验证一个假设，就是入侵植物在进化过程中整个种族的利己性可能会变得越来越强，从而能让自己在现今的入侵地生活的更好。"
针对农业作物，Dudley建议通过亲属识别研究看如何安排亲属植株或者谋生植物之间的种植位置，以提高农作物产量。De Kroon正在研究多品种植株套种。Karban希望能利用有关植物交流的各种观点来改造植物对害虫的自然防御系统。
Karban说："也许在此之前我们认为只有人、脊椎动物或者牲畜才有某些行为，但是也许我们低估了植物，它们的行为可以比我们想像的要复杂。"
