Nod-for-me potion.

A notorious invader called the tree of heaven may have an unusual way of outsourcing some of its nutrient-finding efforts. The Ailanthus altissima trees, like most plants, can't process nitrogen from the air into a usable form. But clovers and many other legumes can with the help of bacteria housed in root nodules. The bacteria snag nitrogen from the air and convert it. Research now shows that trees of heaven exude a substance that revs up the roots of clover plants to form these nodules, Jesse Lincoln of Grand Valley State University in Allendale, Mich., reported July 27. Clover nodules eventually enrich the soil with more user-friendly nitrogen. This trick for enhancing local nitrogen may explain in part how trees of heaven thrive in pitiful soils, suggested collaborator Gary Greer, also of Grand Valley.