Allelopathy Study On Inhibition Mechanism Of Stellera Chamaejasme By Astragalus Adsurgens

Stellera chamaejasme, a typical poisonous weed species in Chinese grassland, directly endangers the life of people and livestock, the ecological environment in pasturing region. It indicates that the pasture seriously become degraded when S. chamaejasme population develops in large scales. In 1970s to 1980s, it had been found in the Northwest of China that the population of S. chamaejasme was inhibited by Astragalus adsurgens reseeded, hence, the degraded grasslands restored in a short time (about 10 a). However, no study was conducted to reveal the mechanism of A. adsurgens inhibiting S. chamaejasme.In this study, the effects of A. adsurgens on cultured shoots from S. chamaejasme were tested by a bioassay using the extracts from sterilized cultured roots and the natural plants of A. adsurgens, according to the theory of plant allelopathy. The results showed that the growth of S. chamaejasme was inhibited by the secondary metabolism productions in A. adsurgens plants. It provides basis for the biological control of S. chamaejasme in degraded grasslands. The main contents, including the results and the conclusions of this study were listed below.1. The allelopathic potential of cultured A. adsurgens rootsLow concentration (3.2 mg/L) of filtrate extracts from A. adsurgens roots culture had weak stimulatory or inhibitory effect on proliferation, elongation, biomass, root elongation and root matter accumulation of cultured shoots from S. chamaejasme. In contrast, the proliferation, elongation, biomass, root elongation and root matter accumulation of cultured shoots from S. chamaejasme were intensively inhibited when the concentration of filtrate extracts was 6.4 mg/L or higher. The inhibitory effect increased as the concentration of filtrate extracts increased.Higher concentration of extracts from cultured A. adsurgens roots or culture filtrates intensively inhibited the seedlings growth of radish and lettuce. However, lower concentration of extracts from cultured A. adsurgens roots or culture filtrates had weak inhibitory effect, or the inhibitory effect became stimulatory effect. In different culture stages, the effect of cultured A. adsurgens roots on seedlings growth of radish and lettuce changed irregularly.2. The allelopathic potential of different parts of A. adsurgensWhen the extracts partitioned from different parts of A. adsurgens with ethyl acetate (1:20) were used at the level of 10 mL/L, the subculture of S. chamaejasme was inhibited obviously. Specifically, the coefficient for virtual proliferation, the height, the fresh weight and the dry weight of cultured shoots from S. chamaejasme decreased 52.0%~78.2%, 27.2%~60.1%, 67.1%~85.5%, 60.2%~81.9%, respectively. The roots formation was not intensively disturbed by extracts from different parts of A. adsurgens (the rooting rate changing in range of -2.6%~9.9%). The root elongation of cultured shoots from S. chamaejasme was greatly stimulated (the root length increase by 22.2%~59.7%), whereas, the matter accumulation in root parts was seriously inhibited (the fresh weight of root decreased by 40.5%-53.5%). Compared with the effects of extracts from other parts of A. adsurgens, the effects of extracts from underground parts were weak.3. The allelopathic potential of A. adsurgens in different growth stagesTreated with the extracts from roots of A. adsurgens in nutritional growth stages, blossom and seed stage, maturing stage, the coefficient for virtual proliferation of cultured shoots from S. chamaejasme decreased by 56.4%, 52.2%, 53.8%, the height decreased by 42.6%, 50.0%, 46.5%, the fresh weight decreased by 69.8%, 64.5%, 68.3%, the dry weight decreased by 68.7%, 67.6%, 64.0%, the 45 d rooting rate decreased by 10.0%, 7.5%, 12.5%, the length of root increased by 44.0%, 31.2%, 57.6%, and the fresh weight of root decreased by 55.6%, 48.5%, 52.7%, respectively. It suggested that there were no obvious differences in allelopathic potential of A. adsurgens in various growth stages on the growth of S. chamaejasme.The result also showed that A. adsurgens in various growth stages had different effects on seedling growth of radish and lettuce. Generally, the effect of A. adsurgens in maturing stage and blossom and seed stage was more intensive than that in nutritional growth.4. The allelopathic potential of A. adsurgens in different growth yearsTreated with the extracts from roots of A. adsurgens in the second, the third, the forth and the fifth growth years, the coefficient for virtual proliferation of cultured shoots from S. chamaejasme decreased by 47.7%, 50.5%, 45.8%, 44.9%, the height decreased by 56.3%, 59.7%, 56.8%, 52.2%, the fresh weight decreased by 61.7%, 75.7%, 60.6%, 60.9%, the dry weight decreased by 64.1%, 71.9%, 57.7%, 59.4%, the 45 d rooting rate decreased by 9.8%, 14.6%, 2.4%, and increased by 2.4%, the length of root increased by 34.8%, 45.9%, 15.6%, 12.6%, and the fresh weight of root decreased by 35.7%, 42.5%, 22.7%, 16.4%, respectively. It suggested that the allelopathic potential of A. adsurgens in various growth years on the growth of S. chamaejasme was not identical. Specially, the allelopathic potential of A. adsurgens in the third growth years on S. chamaejasme was more obvious than that in other growth years.It also indicated that A. adsurgens in various growth years had complicated allelopathic potential on seedling growth of radish and lettuce.