On the surface, trees may look stationary, but underground their roots — aided by their fungal allies — are constantly on the hunt and using a surprising number of strategies to find food, according to an international team of researchers.The precision of the nutrient-seeking strategies that help trees grow in temperate forests may be related to the thickness of the trees' roots and the type of fungi they use, according to David Eissenstat, professor of woody plant physiology, Penn State. The tree must use a variety of strategies because nutrients often collect in pockets — or hot spots — in the soil, he added."What we found is that different species get nutrients in different ways and that depends both on that species' type of root — whether it's thin or thick — and that species' type of mycorrhizal fungi, which is a symbiotic fungus," said Eissenstat. "What we show is that you really can't understand this process without thinking about the roots and the mycorrhizal fungi together."Tree species with thicker roots — for example, the tulip poplar and pine – avoid actively seeking nutrient hot spots and instead send out more permanent, longer-lasting roots. On the other hand, some trees with thinner roots search for nutrients by selectively growing roots that are more temporary, or by using their fungal allies to find hot spots.