| Peanut is one of important crops for food and oil in our country. The harm of weeds is the main reason that leads to the reduction of production and decline in the quality of peanut, even when it caused serious damage to species. Herbicides are widely applied in peanut, but because of inappropriate use, it also brings some negative impacts: reducing the ability of rhizobium-peanut symbiotic nitrogen-fixation, decreasing the N supply, reducing the production and quality of peanut and succeeding crops. The purpose of this paper is to study effect on rhizobium-peanut symbiotic nitrogen-fixation by several herbicides, in order to provide a theoretical basis for the scientific selection of herbicides. In this study,8 herbicides , fluoroglycofen-ethyl, acifluorfen, haloxyfop-R-methyl, quizalofop-P-ethyl, acetochlor, metolachlor, butralin, pendimethalin, were determined on Bradyrhizobium sp. Arachis in vitro; In greenhouse, the height, fresh and dry weight, nodulation after treatment with 8 herbicides were studied; at the same time,leghemoglobin, flavonoid, NRase activity, GS activity and total nitrogen content that were associated with rhizobium-peanut symbiotic nitrogen-fixation and nitrogen metabolism after treatment with 8 herbicides were also studied. The results could be summarized as follows:1.The studies of 8 herbicides on Bradyrhizobium sp. Arachis in vitro showed that the toxicity of 8 herbicides to Bradyrhizobium sp. Arachis was different. Four post-emergence herbicides all had inhibitory effect, four pre-emergence herbicides all had no inhibitory effect at the dosage of 1250mg·L-1, acetochlor and metolachlor had no inhibitory effect at the dosage of 2500mg·L-1. The toxicity of haloxyfop-R-methyl was the biggest, and fluoroglycofen-ethyl was second, average diameter of bacteria inhibiting ring specially was 2.27cm and1.66cm at the dosage of 10000mg·L-1.The toxicity of metolachlor was the least, average diameter was 0.30cm at the dosage of 10000mg·L-1.1. All tested herbicides had different inhibitory effects on height, fresh and dry weight of peanuts, which rose along with dosage. The inhibitory effect of pre-emergence herbicides was lower than that of post-emergence herbicides. 10 days after treatment, quizalofop-P-ethyl had the highest inhibitory effects on the height of peanut, at the dosage of 75.0g a.i/hm2, and its inhibitory rate was 21.92%; acifluorfen had the highest inhibitory effects on fresh weight, at the dosage of 90.0g a.i/hm2, which inhibitory rate was 36.45%; fluoroglycofen-ethyl had the highest inhibitory effects on dry weight and its inhibitory rate was 45.74%,at the dosage of 360.0 g a.i/hm2. Pendimethalin had the minimum inhibitory effects on development of peanut the inhibitory rate of height, fresh weight and dry weight were 8.1%, 9.95% and 19.13% respectively.30 days after treatment, haloxyfop-R-methyl had the highest inhibitory effects on the development of peanut, the inhibitory rate of height, fresh weight and dry weight were 8.1%, 9.95% and 19.13%, respectively. Metolachlor had the lowest effect.2. All tested herbicides at normal dosage had different inhibitory effects on nodulation. At early and middle age after treatment, the inhibitory effects of 8 herbicides on nodulation were relatively significant, and then the nodulation rate increased rapidly lately. The nodulation rate of most treatments reached above 95%, several of which reached to 100%. The inhibitory effect of pre-emergence herbicides was lower than that of post-emergence herbicides. Fluoroglycofen-ethyl had the strongest inhibitory effect, which nodulation rate was 9.42% at 10d and that was 28.6%at 20d. Metolachlor had the lowest effect on the nodulation of peanut, the average number of nodes of which was more than that of the control.3. The primary investigations on the physical and biochemical mechanism that after treatment with 8 herbicides, which led to the different dynamic changes to chlorophyll content,leghemoglobin content, flavonoid content, NRase activity ,GS activity and total nitrogen content in peanut.4.1 The results showed that the chlorophyll content of peanut decreased significantly after the treatment with 4 post-emergence herbicides at the early age, and then increased. The chlorophyll content was almost equal to that of the blank control. Acifluorfen had the highest inhibitory effects on peanut, which chlorophyll content was only 1.14 at 5d treatment and 1.54 mg·g-1 at 10d treatment. And then chlorophyll content of acifluorfen treatment increased at 15d and 20d,which were2.45 and 2.92 mg·g-1 almost equal to those of blank control at the same term. 4 pre-emergence herbicides had different effects on chlorophyll content of peanut. The effect of metolachlor treatment was lowest and chlorophyll content was 1.88 mg·g-1at 15d, 2.04 mg·g-1at 20d, 2.41 mg·g-1at25 d, 2.75 mg·g-1at 30d respectively.4.2 The results showed that leghemoglobin contents of treatments with 8 herbicides were lower than that of blank control. Fluoroglycofen-ethyl had the highest inhibitory effects on leghemoglobin contents of peanut among 4 post-emergence herbicides, which leghemoglobin contents increased gradually from 10d to 25d,but still obviously lower than that of blank control at the same term. The effects of butralin and pendimethalin were worse than those of acetochlor and metolachlor among 4 pre-emergence herbicides. The leghemoglobin content of pendimethalin treatment was 0.373 mg·g-1at 15d, 0.371 mg·g-1at 20d, 0.560 mg·g-1at 30d, 0.675 mg·g-1at 25d respectively.4.3The results showed that all tested herbicides could affect flavonoid content of peanut except metolachlor. The changing trend of flavonoid content treated with 4 post-emergence herbicides was similar to blank control. Acifluorfen had the highest inhibitory effects and the flavonoid content was 0.659% at 5d, 0.898% at 10d, 1.48%at 15d and 1.946% at 20d after treatment, which was lower than that of other treatments at the same terms. The effect of 4 pre-emergence herbicides on flavonoid content of peanut was lower than that of 4 post-emergence herbicides. Metolachlor had the lowest effect on flavonoid content of peanut, and the flavonoid content was 1.21% at 15d, 1.47%at 20d, 2.11% at 25d and 2.26% at 30d, respectively. 4.4The results showed that the NRase activities of 4 post-emergence herbicides treatments were lower than that of the blank control. Acifluorfen had the highest inhibitory effect on the NRase activity of peanut. The NRase activity decreased significantly at the prophase of treatment and got to minimum value 1.53μg/ (g?h) at 15d after treatment. 20 days after treatment, the NRase activity increased but still lower than blank control. The NRase activity of quizalofop-P-ethyl rose slowly and that was higher than blank control at 10d after treatment. The NRase activity of haloxyfop-R-methyl was always decreased and got to minimum value 7.755μg/ (g?h) at 20d after treatment. The changes of NRase activities of 4 pre-emergence herbicides treatments were similar with the blank control. The inhibitory effects on NRase activities of dinitroaniline herbicides were higher than that of acetanilide herbicides. The NRase activity of butralin was 6.721μg/ (g?h) at 15d and 4.271μg/ (g?h) at 20d, which was lower than that of blank control at the same term.4.5The results showed that all tested herbicides had different inhibitory effects on the GS activity of peanut. Among 4 post-emergence herbicides, acifluorfen had the highest inhibitory effect on the GS activity of peanut at the prophase of treatment and the value of GS activity was 2.0182[μg/ (gFW·h)] at 5d after treatment, which was the lowest among all treatments.20 days after treatment, the GS activity rose greatly and the value was close to the blank control. The GS activity of haloxyfop-R-methyl treatment rose slowly and reached to maximum value 4.188[μg/ (gFW·h)], but still obviously lower than blank control. Metolachlor had the lowest inhibitory effects on the GS activity and the GS activity decreased slowly; 20 days after treatment, the GS activity got to maximum value close to the blank control. Butralin had the highest inhibitory effect on the GS activity of peanut among 4 pre-emergence herbicides treatments.4.6The results showed that total nitrogen content of peanut of all tested 4 post-emergence herbicides were lower than that of the blank control, and the effect was present to maximum 10 days after treatment. Acifluorfen had the highest inhibitory effect on total nitrogen content of peanut and the total nitrogen content value was 1.231% at 5d and 1.316% at 10d; the total nitrogen content increased lately and the value was close to the blank control. The 4 pre-emergence herbicides had little influence on total nitrogen content of peanut. The inhibitory effects on total nitrogen content of dinitroaniline herbicides were higher than that of acetanilide herbicides. |
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