关键词: 灌木, “肥岛”, 土壤资源, 空间异质性, 土地荒漠化, 干旱、半干旱区

Abstract: A replacement field experiment was conducted to study the relative competitiveness between three native annual forage species (Sorghum bicolor × Sorghum sudanense, Medicago sativa and Cichorium intybus), and Flaveria bidentis, a new exotic weed invader in North China. To evaluate the competitive responses of target plants and the competitive effects of neighbors, the pairwise plant combinations with F. bidentis were established in plots in five replacement proportion levels (monoculture of forage species and F. bidentis, and mixed culture of forage species and F. bidentis with the proportions of 1∶1, 1.5∶1, and 2∶1, respectively). The results showed that the canopy density of the three forage species increased with replacement proportion, and the growth of F. bidentis was inhibited to different degrees. Of the three forage species, S. bicolor × S. sudanense had superior competitive ability over F. bidentis, because of its earlier emergence and more coverage, and thus, controlled F. bidentis completely, with an inhibition rate of 100% based on biomass production, irrespective of the proportions employed. As for the mixed culture with M. sativa and C. intybus, the aboveground biomass and plant height of F. bidentis were significantly reduced, and the medium replacement proportion (1.5∶1) of the two forage species was the optimal, with the inhibition rate of F. bidentis aboveground biomass and plant height being 87.7% and 96.2%, respectively,compared with the monoculture control. Under the competition with the three forage species, the relative yield of F. bidentis was less than 1.0, indicating that the intraspecific competition of F. bidentiswas more intense than interspecific competition, and thus, this weed invader was effectively suppressed. All the results suggested that establishing these forage species could be a practical technique for restoring or maintaining the biological diversity on the sites having been invaded or easily to be invaded by F. bidentis.

Key words: Shrub, Fertile islands, Spatial heterogeneity, Soil resources, Land desertification, Arid and semi arid regions