Easy There, Bro: A plant can spot and favor close kin

A little beach plant can recognize other plants that grew from its own mother’s seeds, according to experiments on root growth.

BEACH CROWD. When the Great Lakes sea rocket (Cakile edentula var. lacustris) sprouts in a cluster of close relatives, it competes at root level less vigorously than it would among strangers. N. Chu, Dudley

Sibling sea rocket plants don’t compete with each other as fiercely as unrelated plants do, reports Susan A. Dudley of McMaster University in Hamilton, Ontario.

Plenty of research in animals has found differences in responses to relatives versus non-kin. Determining what relationships plants can recognize has been murkier. Flowers of many species can tell their own pollen from that of another plant. Root systems grow differently depending on such factors as whether they bump into themselves or the roots of a neighbor, or even whether that neighbor comes from the local community or a far-flung one. And experiments comparing the abundance of seeds produced by plant clusters have in some cases found differences between clumps of kin and clumps of strangers.

To set up a direct test of kin recognition, Dudley and Amanda File of McMaster worked with Great Lakes sea rocket (Cakile edentula). This shin-high member of the mustard family thrives on the sandy margins of lakes and along the Atlantic shore.

Dudley and File collected seeds from the beach and planted them in groups of kin or non-kin. The researchers put sets of four seeds either in one container or in a cluster of four smaller containers that held the same total volume of a sand mixture.

When the seedlings reached a phase of vigorous root growth, 8 weeks after planting, the researchers painstakingly washed away the soil and dried and weighed the root masses. They found that unrelated plants growing together allocated about 15 percent more resources to root growth than did plants grouped with their siblings. Plants in single containers that prevented root contact didn’t make that extra allocation, regardless of whether their neighbors were strangers, the researchers report online and in an upcoming Biology Letters.

Greater root growth works as a form of competition as plants grab at soil nutrients and water, says Dudley. “It’s like toddlers with cookies.”

The effort put into grabby roots might explain why another lab found clumps of unrelated sea rocket plants less successful at producing seeds than all-kin clumps were, says Dudley. The intense competition among strangers could have drained resources from the non-kin clumps, she speculates.

Ariel Novoplansky of Ben-Gurion University of the Negev in Midreshet Sede-Boker, Israel, who studies self-recognition in plants, says that he’d like to know how Dudley’s plants would have done at producing seeds. Also, finding the mechanism of this kin recognition “is of utmost importance,” he says.

Ragan Callaway of the University of Montana in Missoula has studied root interactions among desert plants. He praises the “really straightforward, simple” design of the new experiment and says it adds to a growing appreciation among scientists of the complexity of plant interactions. “Plant communities are not just a bunch of populations in the same place,” he says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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