| Switchgrass(Panicum virgatum L.), which is an excellent forage plant that can be used for soil and water conservation, is introduced in Loess Plateau. It is necessary to screen the varieties that can adapt the local environment and the effects of switchgrass on the native plants in the process of planting. In order to provide a theoretical basis for the ecological adaptability and effects of switchgrass on native species, the allelopathy in different lines switchgrass was investigated in this paper. Allelopathic potential was evaluated according to the effect of the aqueous extracts from the shoots of 10 lines switchgrass on lettuce(Lactuca sativa L.). The allelopathic potential in different lines or cultivars was different. Cave-in-Rock displayed stronger allelopathic potential than Nebraska 28. The allelopathic effect of lines switchgrass declined with extracts diluted. The aqueous extracts from the switchgrass shoots had a strong allelopathic inhibition on radicle growth with the maximum inhibiting rate(RI) of 60%. In contrast, aqueous extracts from the switchgrass shoots generally promoted coleoptile growth, and the maximum promoting rate(RI) was 48.1%. YQ5, YQ13, Cave-in-Rock displayed strong allelopathic potential, and the germination of lettuce were 65% and 66.7% at the concentration of 0.02 g/ml of aqueous extraction from YQ5 and Cave-in-Rock. Total dry weight of lettuce treated by 0.005 g/ml aqueous extracts from YQ5 and YQ13(13.5 mg and 13.9 mg, respectively) were significantly lower than that of control. Cluster analysis showed that lines or cultivars of switchgrass on-test can be divided into 3 classes: Cave-in-Rock, YQ13 and YQ5 had the highest allelopathic potential among the switchgrass cultivars; YQ12, Nebraska 28, YQ11, YQ6 and YQ4 with the medium allelopathic potential; YQ8, YQ3, YQ2 and YQ1 with the weakest allelopathy.Switchgrass, as introduced plants, can be used as forage, but also has contribution to soil and water conservation. In this study, the American variety(Cave-in-Rock) and two optional lines(YQ3 and YQ13) were the test material that were used for pot experiment to study the effect of nitrogen on switchgrass growth, net photosynthetic rate(Pn), transpiration rate(Tr) and water use efficiency(WUE). The results showed that: When nitrogen content was less than 100 mg/kg, the effect of nitrogen on tillers, height and biomass of switchgrass was not significant; when the amount of fertilizer exceed 100 mg/kg, nitrogen had a significant role in promoting to YQ 3 and Cave-in-Rock and reached a maximum at 200 mg/kg treatment; the tiller, height and biomass of YQ13 performed increased firstly and then decreased as nitrogen fertilizer increases. In this study, nitrogen can increase the net photosynthetic rate of switchgrass and reduce water use efficiency of switchgrass, which the maximum net photosynthetic rate of Cave-in-Rock, YQ3 and YQ13 achieved 26.9, 25.37 and 28.437 μmol CO2 m-2s-1. Switchgrass was still able to maintain a good state of growth and high photosynthetic rate and water use efficiency in low or no fertilization; With increasing the amount of fertilizer, the water use efficiency of Cave-in-Rock and YQ3 showed the same trend, and reached the minimum values(16.311 and 19.642 mmol/mol) at the 100 mg/kg nitrogen treatment. The effect of nitrogen on water use efficiency of YQ13 is not significant. YQ3 and Cave-in-Rock had stronger drought resistance and the physiological indices showed similar variation in response to various nitrogen. YQ13 need less fertilizer and had higher yield.Seeds germination capacity that exposed to environmental stress is an important indicator to judge the environmental adaptability of plants. Different concentrations of NaCl and PEG-6000 were added to simulate the salt stress and drought stress, then analyse the effect of that on germination rate, radicle and germ of YQ13 and YQ3. The results showed that: with the increasing, switchgrass germination rate gradually slowed down. The germination rate dropped significantly and significantly inhibited at the 200 mmol/L treatment. With the concentration of NaCl added to 600 mmol/L, switchgrass seed didn’t germinate. Salinity and drought stress had more infiuence on embryo than radicle; when the salt concentration exceeds a certain range, the length of radicle and germ will increase. With drought stress intensifies, the germination speed and germination rate are gradually reduced; the germination rate was significantly lower than the control and the germination speed significant decline at the 20% PEG treatment; the seed does not germinate at the 30% PEG treatment. In ≥10% PEG concentration range, radicle and germ length were significantly lower than controls. |
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