| With the continuous development of modern agriculture,the application amount of chemical fertilizers continues to increase,which in turn leads to excessive accumulation of Ca(NO3)2 and stresses the normal growth of plants.A large number of studies have shown that when the CO2 concentration increases,the plant biomass and its yield increase,and high concentrations of CO2 can improve the plant's stress resistance.As an economic vegetable,cucumber(Cucumis sativus L.)has more and more facilities for cultivation.Therefore,from the perspective of Ca(NO3)2 stress,the mechanism of CO2 enrichment to alleviate the salt stress of cucumber can be more clearly revealed.In this experiment,cucumber was used as a material to study the growth of cucumber seedlings under CO2 enrichment,and its photosynthetic characteristics,reactive oxygen species metabolism and activity of antioxidant enzyme system in order to further understand CO2 enrichment to alleviate cucumber Ca(NO3)2 laid the foundation for the physiological mechanism of stress.The main findings are as follows:1.Ca(NO3)2 under duress,leaf area of cucumber seedlings and aboveground fresh weight significantly by 17.75%and 41.41%,from the perspective on the microstructure,the thickness of spongy tissue decreased obviously,CO2 enrichment,the leaf area of cucumber seedlings and aboveground fresh weight decreased significantly slowed,was reduced by 14.32%,23.83%,the thickness of spongy tissue slowed down significantly.It is suggested that CO2 plus enrichment can effectively reduce the harm of Ca(NO3)2 stress on the growth of cucumber seedlings.2.Under the stress of Ca(NO3)2,the net photosynthetic rate of cucumber seedlings significantly decreased by 35.84%,and the stomatal conductance and transpiration rate also decreased.After CO2 enrichment,net photosynthetic rate was significantly increased by 43.07%,stomatal conductance and transpiration rate were also significantly increased,single,after CO2 enrichment in cucumber seedling leaf chlorophyll a and chlorophyll b content were significantly decreased by 26.69%and 26.59%.The above results show that CO2 plus enrichment can effectively improve the net photosynthetic rate and stomatal conductance of cucumber seedlings,and the long time of CO2 enrichment treatment may result in light adaptation of cucumber seedlings.3.Under the stress of Ca(NO3)2,the content of superoxide anion free radical O2-and MDA in the leaves and root system increased by 22.64%and 126.38%,and Ca(NO3)2 stress resulted in significant increase of CAT activity in root system.In addition,CO2 could significantly reduce the CAT activity in the root of cucumber seedlings under the stress of Ca(NO3)2 at all times,but even so,the CAT activity was still higher than that of the control group.The activity of superoxide dismutase(SOD)and peroxidase(POD)was significantly increased under Ca(NO3)2 stress,which reduced the content of superoxide anion radical O2-and MDA in cucumber seedlings.It is shown that CO2 and enrichment can effectively remove the active oxygen by increasing the activity of SOD and POD,alleviate the damage caused by lipid peroxidation,furthermore,the inhibition of Ca(NO3)2 stress on the growth of cucumber seedlings was further weakened.4.After CO2 plus enrichment,the content of K+ in the root system of cucumber seedlings increased significantly,and the content of Na+decreased with the extension of processing time.CO2 enrichment and Ca(NO3)2 stress at the same time,the cucumber seedling leaves and roots of reduce the content of K+,Ca2+content in the sixth and the ninth days,significantly lower than that of Ca(NO3)2 stress root Na+ content were significantly lower than that of Ca(NO3)2 stress treatment,and to further reduce the root to the absorption of Mg2+,leaves appear on the sixth day of Mg2+ absorption peak,but the overall absorption intensity is reduced.This indicates that CO2 plus enrichment can reduce the effect of Ca(NO3)2 stress on the growth of cucumber seedlings by reducing K/Na. |
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