Addition of activated charcoal to soil after clearing Ageratina adenophora stimulates growth of forbs and grasses in China.

It is well documented that some non-native invasive species can release allelochemicals into soils at levels that may be phytotoxic. However, it is still not known whether allelochemicals, that remain in the soil after an invasive species has been removed, have long-term allelopathic effects on other plants. To answer this question, 2 native forbs (Sida szechuensis and Artemisia myriantha) and 2 introduced forage grasses (Brachiaria decumbens and Setaria anceps) were grown separately for 2 years in a fi eld that had been infested with Ageratina adenophora (a noxious invasive species worldwide) for more than 10 years. All plants, including both underground and aerial parts, were removed at the beginning of the fi eld experiment. In a separate experiment, allelopathic effects of the fi eld soil on seed germination were determined in the laboratory. Activated carbon (AC) was used in an attempt to eliminate allelopathic effects of A. adenophora. The effects of AC treatments were signifi cant in all variables except crown area. Overall, relative growth rate, above-ground biomass, plant height, branch number, total leaf area, crown area, photosynthesis, seed germination rate, shoot length and shoot dry weight were increased by AC treatment in all species, except for photosynthesis in B. decumbens. These results suggest that allelochemicals of A. adenophora remained in the soil and suppressed other plant species for 2 years after removal of the plants. These fi ndings have signifi cant implications for restoration programs as allelochemicals of A. adenophora can not only facilitate its invasion but also infl uence the efforts of ecological restoration of invaded habitats. Feasible measures, such as cutting and burning invasive plants or using species insensitive to allelochemicals, should be adopted to achieve desired ecological restoration in practice.