普特听力材料：揭秘杂草重生的秘密
我们经常很容易发现，杂草被人们铲除了一段时间后，又会很快长出来。这是为什么呢?接下来，小编带你走进这篇普特听力材料，揭秘杂草重生的秘密。
Crabgrass is an ugly, obnoxious weed that is the scourge of the perfect lawn and its perfectionist gardener. Along with being an eyesore, it’s also responsible for a substantial amount of crop loss on commercial farms.
Weeding Out Competition
Common wisdom says that crabgrass is hard to get rid of because it crowds out the plants around it, and does not allow them to get enough space and nutrients. However, scientists have long wondered if crabgrass dominates your lawn’s real estate by using a technique called allelopathy. This literally means “others suffering,” and occurs when a plant harms another by emitting toxic substances into the environment, usually through the soil.
Researchers from Nankai University, China Agricultural University, and the Chinese Academy of Sciences all found that crabgrass uses this method of “weeding out” neighboring plants.
In their experiment, researchers isolated three chemicals from crabgrass roots and nearby soil, and then added them to potted plants of wheat, maize, and soybeans. Sure enough, the plants treated with crabgrass toxins did not grow as well.
Chemical Warfare
Tests revealed that the compounds reduced the amount of carbon in the soil’s microbial biomass. This means crabgrass can actually change the makeup of the bacteria in the dirt around it. Since plants rely on bacteria in order to absorb key nutrients such as nitrogen and organic compounds, the vicious weed makes life extremely hard on its surrounding neighbors.
So the next time you squirt Round‑Up on that pesky patch of crabgrass, remember that the weed is emitting a little herbicide of its own. It’s chemical warfare, right under your nose.
杂草丑陋而令人生厌。是整齐的草坪和崇尚完美主义园丁的祸害。除了难看之外，它还要为商业农场农作物收成大量受损承担责任。
淘汰竞争
按照常理，这种杂草很难根除是因为它排挤周围的植物使得它们没有充足的生长空间和养料。然而，科学家们一直想知道，这种杂草是否通过使用一种名为植化相克的方法支配你家草坪的居住权。这个术语字面上的意思是"非我族类，连根清除"。当某种植物通过释放有毒物质到环境中(通常通过土壤)来伤害其他植物时，这种现象就在发生。
来自南开大学，中国农业大学，和中国科学院的研究人员都发现这种杂草使用这个方法清除周围的植物。
在实验中，研究人员从这种杂草的.根部和其周围土壤中隔绝出三种化学物质，然后将它们加入盆栽的小麦，玉米和大豆中。不出所料，受这种杂草毒素影响的植物都生长不佳。
化学战争
这些试验揭示了该复合物降低了碳在土壤中微生物生物量中碳的数量。这意味着这种杂草确实能够改变其周围泥土中细菌的组成。因为植物依靠细菌来吸收诸如氮和有机化合物这样的重要养分，邪恶的杂草使它的邻居的生存极为艰难。
所以下次，当你向那一撮讨厌的杂草喷除草剂时，要记住杂草自身会释放一些除草剂。在你的眼皮子底下进行一场化学战争。
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