EUROPEAN and US soils contain different microbes that can dramatically change the rate at which a plant grows. This may help explain why plants that are innocuous on one continent can turn into hugely damaging pests when they reach the other.
Ragan Callaway of the University of Montana in Missoula and his team studied spotted knapweed (Centaurea maculosa), a plant brought to the US 100 years ago, and now a rampant weed.
The researchers compared the growth of knapweed plants in normal and sterilised soils collected from both continents, to see if native microbes helped or hindered plant growth. Plants in sterilised European soils put on a massive growth spurt, growing up to nine times as large as those in normal soil. Plants grown in sterilised US soils showed no increase, or even declined in size.
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Although they cannot be sure, Callaway鈥檚 team suspect that European soils contain microbes that kept the plant in check, while in the US, knapweed roots may be nourished by fungi that parasitise native grasses, passing nutrients to the invaders through shared filaments (Nature, vol 427, p731).