Effects Of Gibberellin (GA₃) On Growth Regulation And Cutting-based Control Of Smooth Cord Grass, Spartina Alterniflora

Spartina alterniflora is one of the most important invasive plant species of the coastal area in China. Biomes, ecosystems, public utilities and economic activities have been seriously affected by infestations of this exotic species Spartina alterniflora. Thus, it is very relevant to take effective measures to control the spread of. Many studies have indicated that a single control treatment is practically insufficient to eradicate an invasive plant. In recent years, more and more research was dedicated to the synergy between various control measures. In this thesis, we combined the cutting and regulation with gibberellin(GA₃) to stop the growth of Spartina alterniflora. We studied the effects of different timings of treatment and concentrations of GA₃ (100 mg/L, 500 mg/L and 1 000 mg/L) on the growth and development of Spartina alterniflora, the integrated effects of GA₃ and cutting against Spartina alterniflora, and the degradation of GA₃ in seawater.The major results are summarized as follows:Effects of GA₃ on the growth and development of Spartina alterniflora. The sensitivity of Spartina alterniflora to GA₃, and the effects of GA₃ on the growth and development of Spartina alterniflora depended on the season and growth stage. Winter seedling germination period (March), booting, heading stage (August), flowering, ripening stage (September) on the relatively low sensitivity to GA₃. Vegetative growth stage (May) on the relatively high sensitivity to GA₃.In March, Spartina alterniflora treated with 1 000 mg/L GA₃ had a significantly higher and tiller number compared to the control (P<0.05), and the soluble saccharide content of the roots was significantly lower than that of the control (P<0.05). After treatments of 1 000 mg/L GA₃ in August, and 500 mg/L or 1 000 mg/L GA₃ in September, also the seed production was significantly higher than that of control (P<0.05); The sensitivity of Spartina alterniflora to GA₃ was relatively higher in May; After treatments of 500 mg/L or 1000mg/L GA₃, the plant height was significantly higher than that of control (P<0.05), but the density, tiller number, soluble saccharide content of roots, fruiting number, fruiting rate, fruiting length and seed production were significantly lower than those of the control(P<0.05). In addition, in the plot which treated with 1 000mg/L GA₃, Spartina alterniflora exhibited lodging, with the rate of lodging as high as 32.25%.Effects of GA₃ on cutting-base control of Spartina alterniflora In May, Spartina alterniflora were treated with 500 mg/L or 1,000 mg/L GA₃ and then cut above ground after 15 d, 30 d and 45 d. These treatments significantly inhibited the density and aboveground biomass compared to controls. The efficiency of cutting was improved significantly when done after 30 d and 45 d, and these treatments were especially effective at controlling the Spartina alterniflora.Residue dynamics of GA₃ in seawater When using a chemical substance, its impact on the environment should be fully considered. The research on the residual dynamics of GA₃ in seawater shows that the degradation of GA₃ is faster in seawater than in pure water. After 30 days, the degradation rate reached 97.85%, and the GA₃ had a half-life of only 6.36 days.From the above results, applying GA₃ in the vegetative growth stage had a greater influence on the growth and development of Spartina alterniflora, and with the cutting method, it could significantly improve the efficiency of cutting, In addition, GA₃ is a micro-toxic chemical which is applied at low concentrations and it rapidly decomposes in seawater. For this reason, methods that integrate the use of GA₃ and cutting have broad prospects for their application against Spartina alterniflora.