Autotoxic and allelopathic potentials of Cistus albidus L.

This study focuses on how allelopathic mechanisms may be involved in the fl oristic composition and dynamics of Cistus albidus shrubbery Allelopathic p otential of essential oils was measured for Lactuca sativa (toxicity for ot her species) and Cistus albidus (self-toxicity). These oils have little eff ect on germination but significantly increase, even in low quantities, the number of unviable seedlings and inhibit normal seedling growth. These resu lts explain, at least partially, the existence of monospecific stands over several years and the lack of natural regeneration of the Cistus albidus po pulations. Bioassays performed using natural aerial leachates of Cistus alb idus revealed no significant effects on the above-mentioned parameters. Lea ching does not seem to be an important means of allelochemicals release. Ne vertheless, essential oils have been quantified in litter and soil, indicat ing a possible occurrence of allelopathy in such ecosystems. (C) Academie d es Sciences/Elsevier, Paris.