[Allelopathy of Ageratum conyzoides. VI. Effects of meteorological conditions on allelopathy of Ageratum conyzoides].

In the field, allelopathic potential of A. conyzoides correlated significantly with sunshine time, temperature and rainfall. Allelopathic potential of A. conyzoides grew in favorable combinate condition of temperature, rainfall and sunshine time, allelopathic potential of A. conyzoides reduced, and vice versa. Allelopathic potential of A. conyzoides decreased because of favorable growing seasons in spring and summer. On the contrary, autumn and winter were unfavorable growing seasons, and the allelopathic potential of A. conyzoides increased. Under laboratory experiments, the volatile oil of A. conyzoides made the tested plants not survive at high concentrations of 300 micrograms.ml-1, but volatile oil of A. conyzoides inhibited the tested plants slightly at low concentrations of 60 micrograms.ml-1. However, under high or low temperatures and shading conditions, inhibitory effects of allelochemicals of A. conyzoides on tested plants intensified significantly at low concentration. It revealed that under unfavorable growing conditions, tested plants resistant ability to the allelochemicals of A. conyzoides decreased. When A. conyzoides and tested plants both grew under unfavorable meteorological conditions, allelopathic potential of A. conyzoides increased, and the tested plants resistant ability to allelochemical decreased. Thus, other plants growing among A. conyzoides in natural community were difficult to grow, and it was relatively improved competitive ability of A. conyzoides in natural communities. Joint effect of allelopathic potential and some meteorological factors such as sunshine time, temperatures, and rainfall was one of the important factors that A. conyzoides was dominated in natural communities.