Plant science for plant people.

Plant soybeans beside a mulberry tree and the tree starts feeding from the soybean's side of the soil. Researchers added traceable nitrogen only to the soybean half of a shared pot, then found it in the mulberry's roots, stems and leaves.

You'd expect the soybean to lose that contest. It gained instead. When the two root systems could tangle freely, the soybeans grew 12.3% more nodules than soybeans grown alone. Nodules are the root swellings where bacteria pull nitrogen out of the air. The soybeans also put on 26.5% more shoot weight, and the genes that build nodules ran more than twice as hard. Together the pair outproduced each crop planted solo.

The same neighborly pattern turns up under Canadian forest canopies. Stands that went from the fewest herb species on the forest floor to a middling mix saw their trees store 15% more carbon over a decade, and mosses added 6%. The boost was strongest on warm, dry or nitrogen-poor ground, where you'd guess small plants would only compete with the trees.

The soybean pays its tree rent in nitrogen and still comes out ahead. If you're planning a food forest, the low plants under your fruit trees may be helping those trees grow.