Study explores plant phenotypic plasticity belowground

When we think of organisms actively searching for resources (foraging) we generally think of things like wolves stalking elk or butterflies finding flowers. Why don’t we also think about plants growing roots through the soil? Although they cannot run or fly, plants forage too, for soil nutrients by growing more roots in response to locally high nutrient levels.

One of the most widely accepted explanations of why plants differ in their ability to place roots selectively in patches is known as the “scale-precision tradeoff” theory. Underlying the theory is the idea that large, dominant plants forage over large distances (“foraging scale”) but are unable to place their roots precisely (“foraging precision”), while small, subordinate plants are able to coexist with the dominants, in part, because they exhibit greater foraging precision.

In an article in the August 2005 issue of The American Naturalist, Steven Kembel and James Cahill test the validity of this foraging trade-off theory using a data set of more than 100 species, compiled from previously published studies. Consistent with other studies, they found that species vary greatly in the precision with which they forage, with grasses generally less precise foragers than broad-leafed plants. However, the ability to forage precisely in response to nutrient patches is completely unrelated to plant size. Surprisingly, most species grew bigger when soil resources were patchy instead of evenly distributed, regardless of whether they were precise foragers or not. This research opens up new avenues of inquiry about the ecological significance of plant foraging strategies.