Allelopathic effect of Ageratina adenophora (Spreng.) leaf litter on four herbaceous plants in invaded regions

The effects of different concentrations of water extracts of A. adenophora leaf litter on the germination and seedling growth of Lolium perenne, Trifolium repens, Galinsoga parviflora and Medicago sativa were determined via laboratory bioassay. The objective of the study was to elucidate allelopathic effects of A. adenophora leaf litter on herbaceous plant in invaded regions. Meanwhile, allelopathic effects of A. adenophora leaf litter on the invaded soil were examined via pot experiments. Results showed that with the exception of L. perenne, there existed significant allelopathic inhibition effects of the water extracts on herbaceous plant seed germination. Inhibition effect increased with increasing concentration of water extract. For the growth of G. parviflora and M. sativa seedling, a significant promotion effect was noted at low water extract concentration. However, herbaceous plant seedling growth (except for L. perenne) was significantly inhibited at high water extract concentration. The effect of water extracts on L. perenne seedling growth was insignificant. Furthermore, pot experiments showed that T. repens seedling growth was significantly inhibited by 50 g·kg^-1 leaf litter. T. repens biomass, however, increased by 71.25% with the addition of active carbon (AC). This further testified an obvious allelopathic inhibition effect of leaf litter on herbaceous plant in invaded soils. By leaf litter decomposition and releasing allelochemicals into soils, A. adenophora inhibited seed germination and seedling growth of accompanying plants, created a favorable environment for invasion and expansion.