Effects Of Soil Nutrition On Relative Competitive Ability Of Seedling Eupatorium Adenophorum, An Alien Invasive Weed, And Ryegrass, Lolium Perenne

Eupatorium adenophorum, crofton weed, invaded mainland China in 1940s, and thereafter has expanded to most of southwest China. The weed colonizes crop land and disturbed ecosystems, causing economic damages to animal husbandry.. Among variety of approaches in a long term commitment to control of this invasive weed, the replacement control is one among others of such endeavors. The ryegrass, Lolium perenne, as a fast-growing economic forage plant, is such a potential replacement plant used to re-colonize habitats where E. adenophorum is mechanically cleared. This study was intended to investigate effects of fertilizers on the relative competitive ability of the ryegrass and E. adenophorum, by a series of de Wit's (1960) replacement series from potted plants to field settings. The results of the study would provide foundation for the replacement control practice of the invasive weed.1. The relative competitive ability of L. perenne and E.adenophorum (Compositae) at different nitrogen and phosphorus levels in seedling stageThe experiment was exercised outdoor with potted plants to investigate the relative competitive ability at different nitrogen or phosphorus levels. The nitrogen and phosphorus levels were each set up as three gradients, full level-the regular concentration, half level-50% of the regular concentration, and low level-10% of the regular concentration, based on the Bollard nutrient solution. The effect of nitrogen was greater on the crofton weed than phosphorus whereas its relative competition was stronger at the low nitrogen level than those at the full nitrogen level and half nitrogen level). The competition ability of the crofton weed was much more reduced in below-ground than in above-ground at all nitrogen levels but similar between below-and above-ground at different phosphorus levels, which suggested that the crofton weed mainly competed with the ryegrass below-ground, probably for nitrogen. The relative competition performances of the ryegrass in mixture were same as that in monoculture at the half-and low-nitrogen levels. However, at the full-nitrogen level the competition ability of ryegrass was significantly reduced. The crofton weed was obviously impacted in height, root length, above-ground biomass, and below-ground biomass at all nitrogen levels and the full-phosphorus level. There were significant differences in the phenotypic performances of the crofton weed amongst different phosphorus levels.2. Effects of fertilizers on the relative competitive ability of the seedling Eupatorium adenophorum, an alien invasive weed, and the ryegrass, Lolium perenne Manipulative field experiments were performed to observe the effect of nitrogen and the phosphorus nutrition on competition between Lolium perenne and the invasive exotic Eupatorium adenophorum at seedling stage. The competitive ability of E. adenophorum was increased with application of nitrogen and phosphate fertilizers based on the relative yield and the relative competition intensity, while that of L. perenne was only slightly increased with application of the phosphate fertilizer. However, L. perenne was more competent than E. adenophorum under any of fertilizing treatments. Morphological characteristics of E. adenophorum were also affected by application of fertilizers. The nitrogen fertilizer significantly enhanced plant height, number of branches, and total biomass, while only high level of phosphate fertilizer increased the biomass; the root/shoot ratio of E. adenophorum diminished with increasing nitrogen fertilizer. We suggest application of phosphate fertilizer to enhance the competitive ability of L. perenne in the substitution control of E. adenophorum in similar environments to this study site.3. Effects of fertilizers and cutting on competitive and growth performances of Lolium perenne and the invasive exotic Eupatorium adenophorum at seedling stageField experiments were carried out in a factor design to investigate effects of fertilizers and ryegrass-cutting on competitive and growth performances of Lolium perenne and the invasive exotic Eupatorium adenophorum at seedling stage The fertilizer and cutting had a significant interaction effect on the relative yield of E. adenophorum but not of L. perenne. Although the fertilization increased the relative competition ability of E. adenophorum, the ryegrass was still a stronger competitor compared to E. adenophorum. The ryegrass-cutting decreased the relative competitive ability of E. adenophorum. Growth performances as measured by plant height, number of branches and biomass in E. adenophorum were highest under fertilizing and no ryegrass-cutting conditions, whereas lowest under no fertilizing and ryegrass-cutting conditions. It is recommended that the ryegrass-cutting and little fertilizing would be used to reduce the competitive performance of E. adenophorum, so as to improve the replacement control by planting L. perenne.