Allelopathic effect of three invasive species on Sal ( Shorea robusta Gaertn f) regeneration: evidence from the controlled experiment

The allelochemicals produced by an invasive species can interfere with the germination and growth of neighboring plants. The problem of Sal natural regeneration in Doon Valley has been a long-standing issue that remains unresolved despite numerous studies on its possible causes. Ageratina adenophora, Lantana camara and Ageratum conyzoides are common invasive species in Doon Valley. However, the allelopathic effect of these invasive species on germination and growth of Shorea robusta, one of the climax species remained unexplored. Thus, the present study was conducted on the allelopathic effect of three invasive species (A. adenophora, L. camara and A. conyzoides) on germination and growth of S. robusta in laboratory and nursery conditions. The leaf leachate of all invasive species was prepared by soaking 300 g of foliage in 600 ml distilled water for 48 hrs and considered as 100% concentration leachate. For bioassay, it was further diluted to 5%, 10%, 15% and 20% concentrations with distilled water (v/v). The results revealed a significant (p < 0.05) concentration-dependent inhibitory effect of all invasive species on seed germination as well as root and shoot growth of S. robusta in laboratory and nursery conditions. The inhibitory effect of leaf leachate was significantly (p < 0.05) higher on root growth than on shoot growth and on collar diameter than on height growth. However, further research is required to study these allelopathic interactions under natural conditions.