Wildfire and carbon neutralize Novel Weapons and harms reproductive potential of an allelopathic invasive plant

Abstract Invasive species are a leading cause of global biodiversity loss, and in Southern California scrublands, black mustard ( Rhamphospermum nigrum ) is a prominent, harmful invasive plant. Rhamphospermum nigrum employs allelopathic Novel Weapons to directly harm heterospecifics via inhibition of germination and indirectly by killing mycorrhizae, generating near monocultures across hillsides. However, active carbon, often deposited by wildfires, is known to bond to and neutralize plant exudates. This led to a hypothesis that active carbon soil amendments neutralize R. nigrum Novel Weapons , and thus, the invasive’s superior competitiveness. In the greenhouse and field, carbon treatments reduced or completely inhibited R. nigrum reproductive potential (Inflorescence) and mitigated some of the invasive’s negative effects on the growth of deerweed ( Acmispon glaber ), a common Southern California native “fire-follower”. Carbon soil amendments, whether administered by hand or by fire, may thus reduce the fitness, abundance, and negative effects of R. nigrum on the native plant community.