Potential of biochar to mitigate allelopathic effects in tropical island invasive plants: evidence from seed germination trials.
Many tropical invasive species have strong allelopathic effects. Pyrolyzed waste biomass ("biochar") has sorptive properties that can reduce the bioavailability of a variety of toxic organic compounds, including pesticides and naturally occurring phenolic acids; however, sorption of allelochemicals has received little attention. Strawberry guava (Psidium cattleianum) and lemongrass (Cymbopogon flexuosa) are important tropical island invasives thought to be allelopathic. Leaf extracts of both species were treated with two biochars (made from maize stalk and coconut husk feedstocks) and applied to maize (Zea mays) and radish (Raphanus sativus) seeds in a factorial design involving leaf extract and biochar dosages. Leaf extracts of both species had large inhibitory effects on germination and seedling growth, particularly at higher dosages, consistent with allelopathic effects. Biochar treatments positively affected seed germination and early seedling development consistent with sorption of these allelochemicals; in some cases, "rescue" effects occurred, in which biochar treatments completely counteracted allelopathic effects. Biochar leachates alone also generally had positive effects on seed germination and seedling development. We conclude that biochars have promise as a tool for combatting invasive allelopathic plants in tropical island ecosystems. The relative ease of biochar production using "low-tech" methods, and multiple benefits of biochar in enhancing soil productivity and carbon sequestration, may make such an approach viable in many developing countries.