The mystery of the Namib Desert's circles

江西 周 倩

在非洲南部的纳米布沙漠，雨季时地上会出现很多圆圈，圈外长草，圈内不长草。科学家一直在研究这些圆圈是怎么形成的。

For over 50 years, ecologists have studied and debated the mystery of the Namib Desert's “fairy circles”.These circular patches (小块土地), mostly barren(不长草的) of grasses, have spread across 1,100 kilometers in the arid grasslands of Southern Africa.

What makes the fairy circles distinctive are the barren patches within them,but the growth of grasses around them is notable as well—they have found a way to thrive in what is considered one of the driest places in the world.In previous research, Stephan Getzin, an ecologist at the University of Göttingen in Germany and lead author of the study, and his team thought that plants in the circles' outer rings had evolved to maximize their limited water in the desert.

For the past three years, Getzin has spent time in Namibia tracking the growth of the grasses to find more evidence for this theory.During the drought season of 2020, the researchers installed sensors that could record the moisture (水汽) of the soil at around 20 centimeters deep to monitor the grasses' water uptake.

Analyzing data from the 2021 and 2022 rainfall seasons, Getzin's team found water within the circles was drying up fast,despite not having any grass to use it,while the grasses on the outside were as strong as ever.Under the strong heat in the desert, these well-established grasses had evolved to create a vacuum (真空) system around their roots that drew any water toward them.Meanwhile, the grasses within the circles, which attempt to grow right after rainfall, were unable to receive enough water to live.

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How did the mysterious circle of the Namib Desert form according to the text?

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