Response Of Green Onion To Soil PH,Lead And Mercury Levels And The Effect Of Sepiolite Alleviation

In order to clarify the effect of soil heavy metal Pb,Hg on the yield quality and product safety of green onion,this paper used the secondary saturated D-optimal design method to study the soil pH?5.5-7.5? and Pb level(0-500mg·kg^-1),Hg levels(0-4mg·kg^-1) on the growth of green onion,Pb,Hg enrichment characteristics and some physiological metabolism,and the application of soil-added sepiolite to alleviate the physiological mechanism of Pb,Hg stress in green onion.The main findings are as follows:1.Under the conditions of this experiment,soil pH and Pb,Hg levels have a significant effect on the growth of green onion,but the effect of Pb,Hg level is greater than pH.With the increase of soil pH,the growth of green onion increased first and then decreased,but it continued to decrease with the increase of Pb,Hg level.2.The regression model of the relationship between the yield and quality of green onion with soil pH and Pb,Hg level was established.The model analysis showed that the effect of soil Pb,Hg level on yield quality was greater than pH,and there was significant interaction between them.In the stress of Pb,Hg,the optimal interaction interval of green onion yield was pH 6.89-7.50,Pb,Hg level was 0,and the yield was 2190.00?2277.71 kg/667m² and 2189.00?2274.71 kg/667m²,respectively.The quality of the onion was generally increased with the increase of pH,but decreased significantly with the increase of Pb,Hg level.3.The mathematical model of the relationship between Pb,Hg content with soil pH and Pb,Hg levels of various organs of green onion was established.The model analysis showed that the Pb,Hg content and accumulation were affected greater by the Pb,Hg level than pH of soil in the various organs of green onion.There was a significant interaction between soil pH and Pb,Hg levels.The Pb,Hg content and accumulation decreased with the increase of soil pH,and increased with the increase of soil Pb,Hg level in the various organs of green onion.The root system is higher,the pseudo stem is second,and the leaves are less.4.With the increase of soil Pb,Hg level,the pigment content and Pn of the green onion leaves were decreased,and with the increase of soil pH,which were increased.For example,when the soil pH was 5.5 and the Pb level was increased from 30 mg·kg^-1 to 500 mg·kg^-1,the chlorophyll content of the leaves of the green onion was increased from 2.91 mg·g^-1 to 2.58 mg·g^-1,the decrease was 12.7%.While the Pn decreased from 20.57?mol·m^-2·s^-1 to 13.4?mol·m^-2·s^-1,which was 52.9%.Under the stress of 500mg·kg^-1Pb,the pH was increased from 5.5 to 6.89,chlorophyll and Pn increased by 1.7% and 5.8%,respectively.The chlorophyll fluorescence parameters Fv/Fm and?PSII of the green onion leaves also had similar trends,while NPQ was reversed.5.Under the condition of no application of Pb,Hg in soil,pH 5.5 and pH 7.5 had no significant effect on MDA content and SOD,POD and CAT activities in roots and leaves of green onion,but Pb,Hg stress significantly affected MDA content and antioxidant enzyme activity.In the early stage of stress,the activity of SOD,POD and CAT increased in leaves and roots of green onion,but its activity decreased significantly in the late stage of stress.Under the stress of 500 mg·kg^-1 Pb,the SOD activity of soil pH 5.5 was lower 12.1% than that of pH 6.89.However,under the stress of no Pb,Hg,the activities of SOD,POD and CAT in leaves and roots of green onion did not change significantly.6.Under soil Pb,Hg stress,adding sepiolite can maintain high activity of SOD,POD and CAT in the early stage of growth of green onion,which can improve the ability of green onion to remove O₂^-and H₂O₂,reduce MDA content,and the effect of alleviating Pb,Hg stress was enhances with the increase of the amount of sepiolite.However,as the Pb,Hg stress time progressed,the activity of SOD,POD and CAT began to decrease.Under the stress of 4mg·kg^-1 Hg,the antioxidant enzyme activity of the treated with sepiolite 3mg·kg^-1 was significantly higher than that of other treatments.Under soil Pb,Hg stress,adding sepiolite is beneficial to increase the pigment content of green onion leaves and maintain higher Pn,Fv/Fm and ?PS?.For example,under the stress of 500mg·kg^-1Pb,the Pn of the green onion leaves treated with sepiolite 1,2,3g·kg^-1 increased by 25.6%,30.3% and 36.9%,respectively.And under the stress of 4mg·kg^-1 Hg,they increased by 21.4%,28.6% and 34.3%,respectively.