| In order to investigate the effects of soil heavy metal Pb on the yield,the quality of garlic,and the safety of products,the design of double orthogonal regression method was used in this paper to study soil pH?5.57.5?and Pb levels(30500 mg·kg-1)interactions on‘Jinxiang Zi Pi'and‘Zaotai No.2'garlic's growth,plant Pb enrichment and physiological metabolism.The main results are as follows:1.Soil pH and Pb levels significantly affected the growth of the two varieties of tested garlic,and the effect of Pb levels was greater than pH.The growth of both garlic varieties increased at first and then decreased with the increase of pH,but they all decreased with the increase of Pb levels.2.The regression models of the relationship between the yield,quality of garlic bulbs,garlic scapes and the soil pH and Pb levels were established respectively.After the model analyzed,the effect of Pb was greater than pH,and there was significant interaction effect between them.When the soil pH was less than 6.50 and the level of Pb was lower than 72.3mg·kg-1,the yield of‘Jinxiang Zi Pi'garlic increased with the increase of them,while the yield of‘Zaotai No.2'garlic decreased with the high level of Pb,and the yield of garlic scapes also had a similar trend.The comprehensive quality of bulbs and garlic scapes in two different varieties of garlic increased with the increase of pH,and all decreased rapidly with the increase of Pb levels.3.The content of Pb in each organ of the two tested garlic increased significantly with the increase of soil Pb content and growth,and the roots were higher,the bulbs were the second,and the stems,the garlic scapes and the leaves were less.According to the computer simulation budget,the effect of soil Pb levels on the Pb content of each organ of two tested garlic was significantly greater than pH.If the soil Pb level was 234.09,357.71 and 500mg·kg-1,the Pb content of‘Jinxiang Zi Pi'garlic bulb was 1.10,3.47,6.93 mg·kg-1,and the‘Zaotai No.2'garlic bulb was 2.24,5.15,9.14 mg·kg-1 respectively;When soil pH was 5.5,6.37 and 7.5,the Pb content of‘Jinxiang Zi Pi'garlic bulb was 3.32,1.91,1.67 mg·kg-1,and the‘Zaotai No.2'garlic bulb was 4.42,3.21 and 2.93 mg·kg-11 respectively,indicating that there was a negative correlation between soil pH and the enrichment of Pb in garlic organs.4.With the increase of Pb levels,the leaves pigment content and Pn decreased significantly,such as when soil pH was 5.5,Pb levels were 30,500 mg·kg-1,the content of chlorophyll and carotenoid content of‘Zaotai No.2'in garlic scape extension were 0.91,0.13mg·g-1and 0.58,0.08 mg·g-11 respectively,and the latter decreased by 36.3%and 38.5%compared with the former.Under the Pb stress was 500 mg·kg-1,the pigment and Pn of garlic leaves treated by pH 5.5 were significantly lower than that of pH 6.89.The chlorophyll content and Pn in the leaves of‘Jinxiang Zi Pi'garlic decreased by 35.1%and 23.3%respectively in the bulking stage of the bulbs,and‘Zaotai No.2'decreased by 25.4%and17.2%respectively,and the changes of the chlorophyll fluorescence parameters of the garlic were similar.5.Without external application of Pb,pH 5.5 and pH 7.5 had no significant effect on MDA content and SOD,POD,CAT activity in roots and leaves of two varieties of garlic,but Pb stress significantly affected its MDA content and anti-oxidant enzyme activity.The activity of anti-oxidant enzymes in leaves and roots of garlic increased during the early period of stress,but with the prolongation of time,the activity of anti-oxidant enzymes was significantly decreased,the membrane lipid peroxidation was intensified and the content of MDA increased significantly.At the same Pb stress was 500 mg·kg-1,the anti-oxidative enzyme activity of the soil treated with pH 5.5 was lower than that of pH 6.89.Therefore,the former had higher lipid peroxidation and higher MDA content. |
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