Competition Relationship Between Invasive Species-Xanthium Spinosum And Citrullus Lanatus

Spiny Cocklebur (Xanthium spinosum), which is native to the South America, is a malignant weeds with strong invasive ability and it has been widely spread in the world. It is also one of the fastest spreading and most potentially harmful invasive species in Xinjiang. This research revealed the law of Xanthium on the growth and enzymes activities of Citrullus, including competition mode for it, and explored the affection of Xanthium invasion on oasis farmland ecosystem through pot tests. Several protective enzymes, the part on the ground and underground biomass of Citrullus in different growth periods were determined by setting singal and mixed planting density gradient of Xanthium and Citrullus, under the conditions of adding activated carbon and without activated carbon in the soil, and finally reached the following results:1. Results of plant competitive ability:(1) in the condition of without adding activated carbon, the biomass of Citrullus reduced as the planting density increased, and the differences were significant at high planting density. In various mixing density, there was larger intraspecific competition than interspecific competition between the two species; the competitive attack of Xanthium was greater than that of Citrullus.(2) in the conditions of adding activated carbon, the biomass of Citrullus were higher than that the condition of without activated carbon; either the condition of adding or not, the intraspecific competitions of Xanthium were always higher than interspecific competitions; adding activated carbon reduced the competitive attack of Xanthium on Citrullus, the differences were especially significant when the planting density ratio were1:1and3:1.2. The results of physiological indexes in different growth periods:(1) under the condition of non-carbon, the MDA content of Citrullus with monoculture performed the trend of reducing at first and then rising with the growth circle. While under the condition of activated carbon, it increased gradually. When mixed, the MDA content of in various densities increased, decreased continuously, decreased first and increased later with the increasing of planting proportion, at the same growth period. The MDA content of Citrullus was higher in the vegetative growth phase in high density (8plants/pots).(2) Adding activated carbon could influence and improve the SOD activity of Citrullus, which was especially significant in vegetative period and fruiting period. As the flowering period coming, the SOD activity of Citrullus was lower than that of monoculture in mixed planting condition. The SOD activity of Citrullus leaves was affected generally obvious in low density, too. But the monoculture was relatively high in high density.(3) Adding activated carbon affected the POD activity of Citrullus leaves more notable during the vegetative period. The POD content of Citrullus in carbon-free condition of monoculture was significantly lower than that of adding activated carbon in the medium and high density. The POD content of Citrullus in mixed planting condition was lower than monoculture of Citrullus in different growth periods in medium planting density. In high planting density, the POD content of Citrullus in mixed planting condition was lower than that of monoculture in flowering and fruiting periods. When Citrullus and Xanthium were mixed planted, Xanthium had the largest influence on the POD content of Citrullus at the ratio of1:1in low and high density and especially significant in the period of the fruiting.(4)Without activated carbon, the CAT content of Citrullus in mixed planting condition was generally higher than that of monoculture. Under the condition of adding activated carbon, the CAT content of Citrullus decreased gradually with planting density increasing in vegetative period. While in the flowering and fruiting periods, it increased first and then decreased. As the continuing of growth period, the CAT content of Citrullus began to drop from flowering period. In fruiting period, no matter single or mixing planted, the CAT content of Citrullus in carbon-free condition was higher than that of activated carbon processed ones.