Promising biocontrol effects of a native hemiparasitic plant against a non-native C4 grass.

Hemiparasitic plants are known to be able to diversify degraded grasslands by lowering the competitive power of dominant grasses. Recent research indicates that hemiparasites may also be used against invasive alien plants. Here, we tested the effects of Odontites luteus, a native European hemiparasite, on Sporobolus cryptandrus, a recently established and rapidly spreading C4 grass of North-American origin. We found that Odontites considers Sporobolus a suitable host and reduces its biomass production (and potentially its competitive ability) by approx. 50%, equaling the effect on its major native host, Festuca vaginata. However, Festuca showed severe metabolic impairment (reduced photosynthetic capacity and increased physiological stress) under hemiparasite pressure. So, the application of hemiparasites is a promising biocontrol tool against Sporobolus (and potentially other invasive C4 grasses), but it is not a silver bullet. We cannot expect a full eradication of the invasive species and a recovery of the native community but thinning monodominant Sporobolus stands to allow certain populations of native species, particularly those resistant to Odontites, to come back is a more realistic goal. This could lead to a partial recovery of the former species composition and an improvement of ecosystem functions, such as providing food for pollinators.