| Chinese cabbage,one of the most widespread economic crops,is widely planted in China greenhouse cultivation.Chinese cabbage facility cultivation appear increasingly serious continuous cropping obstacles,especially the secondary salinization of soil on account of the enlargement of the planting area and the increasing multiple crop index.Excessive Ca(NO3)2 not only seriously affect the production of Chinese cabbage,but also lead to excessive nitrate accumulation in vegetables,which cause serious damage to human health.Chinese cabbage was selected as test materials and hydrogen gas(H2)was applyed in the form of hydrogen-rich water(HR\W).The main purpose of this paper was to explore the mechanism of H2 relieve the Ca(NO3)2 stress and reduce the nitrate content in Chinese cabbage.The main results are as follows:1.Ca(NO3)2 stress significantly inhibited the growth of Chinese cabbage seedlings,mainly in dry weight and fresh weight reduced,root length shorted,net photosynthetic rate(Pn)declined,reactive oxygen species(O2·-,H2O2)content increased,malondialdehyde(MDA)content increased and leaf relative electrical conductivity enhanced.However,HRW significantly improved the growth and photosynthetic capacity of Chinese cabbage compared with the single Ca(NO3)2 stress treatment.At the same time,antioxidant enzymes activity was increased significantly.Accordingly,ROS content and leaf relative conductivity was decreased significantly under the co-treatment of HRW and Ca(NO3)2 stress.More significant,HRW also dramatically increased the activity of NR and then reduce the nitrate content in the leaves and roots.The above results showed that exogenous HRW can enhance the photosynthesis,improve the antioxidant enzyme activity to reduce the accumulation of reactive oxygen species and alleviate the membrane lipid oxidative damage,improve the activity of nitrate reductase to reduce the nitrate content,so as to improve the resistance of Chinese cabbage seedlings to Ca(NO3)2 stress,ultimately promote the growth and development of Chinese cabbage seedlings.2.Excessive Ca(NO3)2 will cause osmotic stress,metabolic disorders,thereby disturb the absorption of other mineral element.At the same time,excessive nitrate residue in vegetables can seriously reduce the nutritional quality and threaten people's health.So,the main aim of this part of the study was to explore HRW is how to regulate the absorption,transport and metabolism of nitrate in Chinese cabbage and provide the theoretical basis for HRW application in facility agriculture.The results showed that HDRW significantly reduced the nitrate content in leaves and roots under Ca(NO3)2 stress.In the leaves,HRW promoted the nitrate metabolism and reduced transportion of NO3-to mesophyll cell by activating the activity of NR and GS.In roots,HRW did not influence nitrate absorption in view of nitrate absorption curve and NRT1.1 gene expression had no significant difference under the co-trearment of HRW and Ca(NO3)2 stress.But,HRW significantly inhibited NRT1.5 gene expression and promoted the NRT1.8 gene expression under Ca(NO3)2 stress.Corresponding,HRW significantly improved the root-shoot ratio by calculating the proportion of nitrate content in root and leaf.At the same time,HRW further improve ascorbic acid,soluble protein and sugar content.The above results manifested that HRW can reduce the nitrate content of Chinese cabbage leaves by promoting nitrate metabolism in the leaves and inhibiting nitrate transport to the ground in the root.Finally,mineral elements absorption were measured in Chinese cabbage seedlings.The results showed that HRW significantly increased Mg content,further increased Zn content which illustrated HRW can partly adjust disorder of mineral elements absorption caused by Ca(NO3)2 stress in Chinese cabbage seedlings. |
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