Plants produce a lot of chemicals. I mean a lot. Some of these are involved in day to day functions like growth and reproduction. The function of others can be a bit less obvious. These are often referred to as secondary compounds as they are not directly involved in growth or reproduction. Some of these chemicals are toxic to other plants. We call these compounds allelochemicals. Producing allelochemicals can give some plants a competitive advantage by knocking back their neighbors. However, like most things in ecology, this situation isn't always that simple.
Take the example of spotted knapweed (Centaurea maculosa). This nasty invader is wreaking havoc on plant communities throughout western North America. It wages its war under the soil where it releases a chemical from its roots called "catechin." This chemicla kills native plants, especially native grasses growing nearby. This competitive advantage can lead to total dominance of spotted knapweed in many areas where it quickly rises to monoculture status.
Not all native plants are equally susceptible to spotted knapweeds effects. Two native forbs stand out above the rest in being able to cope with the allelochemicals released by spotted knapweed. Enter silky lupine (Lupinus sericeus) and blanketflower (Gaillardia grandiflora). Where these plants occur alongside spotted knapweed, other natives seem to do a bit better. This made researchers curious. What was it about these two species?
As it turns out, both of these natives secrete their own chemicals. These don't act as allelochemicals though. Instead, it was found that they neutralize the detrimental effects of the catechin. In doing so, both the lupine and the blanketflower create a safe zone for other natives to reestablish. This could be good news as it hints at new ways of approaching certain plant invasions. More work needs to be done to see how well this situation plays out in a natural setting but the evidence is tantilizing to say the least!
Further Reading: