Study On The Relieving Effect Of Fulvic Acid On Calcium Nitrate Stress Of Brassica Campestris L. And Its Mechanism

Secondary salinization is one of the main causes of vegetable continuous cropping disorder.However,the unreasonable application of nitrogen fertilizer leads to the formation of soil secondary salinization,excessive Ca(NO3)2 has serious adverse effects on vegetable growth and nutritional quality.In this study,by determining the effect of different concentrations of calcium nitrate on the Brassica Campestris L.growth index,The concentration of calcium nitrate on Brassica Campestris L.stress was selected;By measuring the growth index of the nine cabbage heart varieties,preliminary comparison of differences in tolerance to Ca(NO3)2,resistant Ca(NO3)2 varieties and sensitive Ca(NO3)2 varieties were selected;Compare the photosynthetic characteristics,MDA content,relative conductivity,histochemical staining,SOD,POD,CAT,APX activity,root activity,nitrate content and nitrate reductase activity of Ca(NO3)2 varieties and those sensitive to Ca(NO3)2 under Ca(NO3)2 stress conditions,The mechanism of Ca(NO3)2 resistance was preliminarily clarified;With the Ca(NO3)2 sensitive variety as the test material,To determine the growth index of Ca(NO3)2 stress treated with different concentrations of fulvic acid(FA),The optimal remission concentration of FA was selected;at the same time,To determine the growth index,photosynthetic characteristics,MDA content,relative conductivity,histochemical staining,SOD,POD,CAT,APX activity,root vitality,nitrate content and nitrate reductase content of aboveground and lower parts under calcium nitrate stress,The mitigation mechanism of fulvic acid on calcium nitrate stress was preliminarily revealed.The main results are as follows:(1)Ca(NO3)2 concentration is 80 mmol·L-1,the growth of Brassica Campestris L is significantly inhibited,and the fresh weight of the lower part of the ground decreased by 45.8%and 51%,respectively.(2)Compared with the 15 mmol·L-1 Ca(NO3)2 treatment,the variety Lianzhou F1’ showed no significant difference in root length,dry and fresh weight of above-ground part and dry and fresh weight of underground part under the 80 mmol·L-1 Ca(NO3)2 treatment,so ’Lianzhou F1’ was selected as the variety resistant to calcium nitrate in subsequent tests.Compared with 15 mmol·L-1 Ca(NO3)2 treatment,the variety ’Jinqiu Red No.2 red’ showed significant differences in root length,plant height,root dry and fresh weight and shoot fresh weight under 80mM Ca(NO3)2 treatment.Therefore,’Jinqiu Red No.2 red’was selected as the variety sensitive to calcium nitrate in subsequent experiments.(3)Compared with the 15 mmol·L-1Ca(NO3)2 treatment,The stomatal conductivity and transpiration rate of the variety ’Jinqiu Red No.2 red’ were reduced by 1.27 times and 1.09 times,respectively,The variety ’Lianzhou F1’ stomatal conductivity and transpiration rate were reduced by 24%and 20%respectively;The MDA and relative conductivity content of the variety "Jinqiu Red No.2 Red" is higher than the variety ’Lianzhou F1’;O2· and H2O2 accumulated less in the leaves of the variety’Lianzhou F1’;Under the stress of Ca(NO3)2,The nitrate content of ’Lianzhou F1’ is 36%lower than the lower part of ’Jinqiu Red No.2 red’ seedlings,The activity of nitrate acid reductase(NR)in the lower part of ’Lianzhou F1’ was increased more.Under Ca(NO3)2 stress,’Lianzhou F1’ has stronger photosynthetic capacity,lower membrane lipid peroxidation,higher antioxidant enzyme activity,stronger root activity,better nitrate reduction capacity,and better resistance to Ca(NO3)2.(4)When the concentration of fulvic acid(FA)was 100 μgmol·L-1,the root length and the dry and fresh weight of shoot and root parts were significantly relieved,which increased by 26.67%,49.2%,56.47%,56.91%and 58.31%.Therefore,100 μmmol·L-1 fulvic acid was selected as the subsequent relieved concentration.(5)When Ca(NO3)2 was added in excess,FA could effectively reduce the growth inhibition of cabbage seedlings by increasing root length,plant height above-ground fresh weight and underground dry and fresh weight.FA inhibits the accumulation of H2O2,O2·-and MDA and the increase of relative conductivity under Ca(NO3)2 by increasing the activity of antioxidant enzymes(SOD,POD,CAT and APX)which increased by20%,22%,15%and 57%.FA promotes the reduction of nitrate by increasing the activity of nitrate reductase,and at the same time reduces absorption and transport to the ground through transporter(BcNRT1.l and BcNRT1.5),so that nitrate is stored in the root;FA can increase the transport of P,K and Fe from the underground to the above ground under Ca(NO3)2 stress.