| Cogongrass [Imperata cylindrical (L.)], also called Japgrass, blady grass, speargrass, and lalang-alang, a common weed in the family Gramineae, is a perennial herb. Because of its long and strong root, it is very hard to root out. It has been reported as one of the ten most troublesome weed species in the world. Therefore, developing an effective method to control this weed has become a significant and worthwhile practice.Croftonweed [Eupatorium adenophorum Spreng.=Ageratina adenophora (Spreng.) King&H.E. Robins.], a worldwide noxious invasive weed, is an erect perennial herb native to Mexico and Costa Rica of Central America. Because of its stress tolerance, large number of cypselas and marked ability to regenerate from stems and roots; it has spread over large areas of the world. As an invasive species, it threatens the biodiversity security in Southwest China, and has caused great economic losses. Together with other three invasive external species, the weed has been listed in the White Paper by The State Environmental Protection Administration of China. Now, there has no effective method to control this weed.In this study, the author use different concentrations of glyphosate to treat croftonweed and cogongrass, and then investigated the photosynthesis, chlorophyll fluorescence characteristic, indexes of the shikimic acid pathway and other physiological indexes of the plants order to research how the glyphosate influence these weeds, at the same time, find the effective method to control these weeds. The results are as follows:1) Glyphosate resulted in significant influence of the physiological indexes in the plantlets of croftonweed and cogongrass. The fresh/dry weight value decreased with the increased concentration of glyphosate and increased processing period. The chlorophyll a and b content decreased after treated with glyphosate, while the proline and soluble sugar content increased after treated with glyphosate. The SOD activity increased at first time and then decreased with the glyphosate concentration increased.2) Glyphosate resulted in significant influence of the photosynthesis in croftonweed and cogongrass. The results showed that the glyphosate decreased the net photosynthetic rate (PN) of leaves of the cogongrass, while decreased the transpiration rate (E) due to the leaves epidermis damage and stomata closed at first time, and then increased on account of the stomata damage. The response curves of net photosynthetic rate (PN) to different photosynthetic photon flux densities and and different concentration of CO2in leaves of croftonweed which treated with different concentration glyphosate showed that the glyphosate reduced the light saturation point (LSP), while increased the light compensation rate (LCR) of the leaves of croftonweed.3) After treated with different concentrations of glyphosate, the Quantum yield (yield), electron transport rate (ETR), photochemical quenching (qP), and nonphotochemical quenching (NPQ) response to photon flux density (PPFD) decreased with the increased of concentration of glyphosate.. These results showed that with increased concentration of glyphosate and increased processing period, PSII reaction centers gradually closed resulting in a decline of electron transport rate and quantum yield, and even damage of thylakoid membrane integrity. At the same time, the capacity to utilize high light intensity was weakened. The most obvious variation we can observe was in the third period (9d after treatment). The quantum yield (yield), apparent electron transport rate (ETR), photochemical quenching (qP), and nonphotochemical quenching (NPQ) of these two weeds were lowest. The integrity of thylakoid membrane was severely damaged, the PSII reaction centers almost completely closed and electron transport was disappeared.4) The shikimic acid content of croftonweed and cogongrass witch treated with different concentrations of glyphosate increased with the increase of glyphosate concentration, the tryptophan content has the reversed tends. Our results showed that the glyphosate influence the shikimic acid pathway of plant.5) All the four different concentrations of glyphosate could kill the aboveground parts of these two weed, while0.3%and0.5%concentration of glyphosate could not kill the rhizome of these weeds, the survival rates of croftonweed and cogongrass witch treated with0.3%concentration of glyphosate in March of the next year were35.7%and41%, respectively. The group witch treated with0.5%concentration of glyphosate were20%and13%, respectively, while the1.0%and2.0%concentration of glyphosate could be the effective to kill the cell of rhizome and the whole plants. |
PDF Full Text Request