| Eupatorium adenophorum, as a kind of noxious intrusive weed, is distributed widely in Yunan, Guizhou, Sichuan, Guangxi, etc, of China, causing big damage to local forestry and husbandry, and huge impact on ecological system. Replacement control is applied generally due to its lasting efficient results, ecologcial and financial benefits.Two fast-growing, large-biomass, good-covered grass, Dolichos lablab and Paspalum wettsteinii, were selected to compete with E. adenophorum in pot and Multiple De Wit replacement design was carried out to study competition effect of soil after intrusion by E. adenophorum, N-fertilizer, mixed proportion and densities on replacement plants and E. adenophorum in terms of Relate Yield (RY), Related Yield Totals (RYT), Mean Aggressive Index (A). Some limitations of index evaluating the relative growth of plants was found. The plaination was given and solution was proposed. The results were demonstrated as followed:1. Comparison of phenotype features among different speciesThe plant height and biomass of two replacement plants were significantly larger than that of E. adenophorum. Specifically, the average plant height and biomass of D. lablab is 4.65- and 20.18-fold, respectively, larger than that of E. adenophorum, and the average plant height and biomass of P. wettsteinii is 3.98- and 22.15-fold, respectively, larger than that of E. adenophorum. Soil treatment reduced the difference of plant height and biomass between the replacement plants and E. adenophorum. Conversely, fertilizer treatment increased the differences of the same parameters as above between the two groups.The plant height and biomass of E. adenophorum, when mix-planted with D. lablab, was larger than that of with P. wettsteinii. However, there was no significant difference between them. The plant height and biomass of D. lablab were larger than that of P. wettsteinii.2. Effect of proportion on phenotype featuresThe plant height and biomass of replacement plants were enhanced conversely with the proportion. The two parameters achieved the highest values when replacement plants to E. adenophorum proportion equaled 1:3, and were significantly larger than other proportions. The plant height and biomass of E. adenophorum were the largest when planted singly, and was larger significantly than all mix-planted proportions. There were no significant differences among the mix-planted proportions, showing similar control effect of replacemenr plants among different mix-planted proportions.Compared with planted singly, the plant height and biomass of E. adenophorum when mixed with D. lablab were decreased by 56.88% and 93.71%, respectively, and by 27.50% and 77.26%, respectively, when mixed with P. wettsteinii, demonstrating the higher control capacity of D. lablab than that of P. wettsteinii. The control capacity of replacement plants on plant height of E. adenophorum was higher than that of them on biomass, illustrating more resource was assigned by E. adenophorum to plant height, which told us that E. adenophorum possessed the potency of phenotypic plasticity, which might be one of intrusive mechanisms.3. Effect of density, soil and fertilizer on phenotype featuresThe biomass of replacement plants was decreased significantly by intrusive soil, but unchanging for that of E. adenophorum, showing the competition capacity of replacement plants was reduced by intrusive soil; Fertilizer increased significantly the biomass of replacement plants and E. adenophorum, increased the biomass of D. lablab and E. adenophorum respectively by 73.3% and 52.6% and increased the biomass of P. wettsteinii and E. adenophorum respectively by 140.7% and 60.0%. As a result, the biomass increase ratio of replacement plants by fertilizer is larger than that of E. adenophorum, showing the competition capacity of replacement plants was increased by fertilizer. It's found that biomass of each proportion variation changed with equal ratio but inequality through analyzation of effect of soil and fertilizer on the biomass of replacement plants.High density not only significantly limited the plant height and biomass of replacement plants, but also do the biomass of E. adenophorum. Oppositely, no significant restriction for plant height of E. adenophorum, indicating E. adenophorum to some extent possessed phenotypic plasticity on density.4. Effect of parameters on competition indexExcept for few treatments, the relative yields of replacement plants were larger significantly or extreme significantly than 1, and increased inversely with the proportion, accounting for the larger intraspecific competition than interspecies. Replacement plants were benefited by mix planted method; the relative yields of E. adenophorum were lower extreme significantly than 1, accounting for the lower intraspecific competition than interspecies. E. adenophorum were undermined by mix planted method. Proportion had no effect on the relative yield of E. adenophorum.5. Invalid related competition indexThe competition capacity of replacement plants was reduced by intrusive soil, and strengthened by fertilizer, but wasn't reflected by A. It's found that relative yield and its derived index could work in one replacement series, however, when competition effect was compared among two or more replacement series and the biomass of each proportion changes with equal ratio but inequality, indexes to evaluate the relative growth of plants, such as relative competition intensity, relative yield and its derived index, were invalid. It worked to explain the state by absolute competition intensity (ACI) or biomass. |
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