Study On Physiological Response Of Sweet Pepper Seedlings Under Nitrate Stress And Mitigation Effect Of Diatomaceous Organic Fertilizer

In recent years, the greenhouse cultivation of China develops rapidly and soil secondary salinization in protected farmland is becoming worse. Soil salinity is problem of vegetable cultivation being solved and has become the bottleneck for sustainable development of greenhouse cultivation, and cause widespread concern. In this paper, indoor culture experiments, hydroponic experiments and pot experiments are carried out to study on the impact of soil salinity of fertilize, nitrate stress on the damage mechanism of sweet pepper seedlings, and diatomaceous organic fertilizer on some physiological and metabolic effects of sweet pepper seedlings under nitrate stress, aim at offering the theoretical basis on the improvement of soil secondary salinization in protected farmland and the utilization of waste diatomaceous earth. The main results are as follows:1 Effects of fertilization on the soil salt content and composition1.1 Indoor culture experiments results showed that, under the same amount of nutrient applied, soil conductivity and salt content of treatment of different nitrogenous fertilizer were in the order: NH4Cl>(NH4)2SO4>NH4NO₃>CO(NH2)2, NH4HCO₃. Nitrogenous fertilizer species to affect the soil pH led to differences in soil salinity. Soil conductivity and salt content of treatment of different phosphate fertilizer were in the order: calcium superphosphate>calcium magnesium phosphate; soil conductivity and salt content of treatment of different potassium fertilizer were in the order: K2SO4>KCl. The effects of the same amount of organic fertilizer on soil conductivity and salt content were in the order: chicken dung > rapeseed cake > pig dung, cow dung.1.2 Application of nitrogen, phosphorus and potassium fertilizer and organic manure could increase soil salt-ion content. The major cation in soil was Ca2+,K+ , and the main anion was NO₃-. To reduce soil secondary salinization in protected farmland, we should choose CO (NH2)2 in nitrogenous fertilizer; we should choose calcium superphosphate in phosphate fertilizer; and we should choose K2SO4 in potassium fertilizer. In soil of secondary salinization, application of cow dung and other high C/N ratio and low nutrient content of organic fertilizer could reduce soil salinization.2 The physiological response of sweet pepper seedlings under nitrate stress2.1 Hydroponic experiments results showed that, the growth of sweet pepper seedlings was inhibited under nitrate stress, and plant height, stem diameter, fresh weight root volume and root activity of sweet pepper seedlings were reduced significantly with the concentration of Ca(NO₃)2 in the medium increased.2.2 Nitrate stress led to SOD, POD activities increased, CAT activities decreased, O2·- producing rate and H2O2 and MDA content increased of sweet pepper seedlings, which eventually caused membrane lipid peroxidation and membrane system damage.2.3 Compared with CK, the nitrate reductase activity of treatment with 60mmol/L Ca(NO₃)2 increased 10.06%, and the difference was not significant. The nitrate reductase activity of treatment with 80 mmol/L, 120mmol/L, 150 mmol/L Ca(NO₃)2 decreased by 16.87%, 40.62%, 63.88%, and the differences were significant or highly significant.2.4 Under nitrate stress, stomatal conductance and the content of Chla, Chlb, Chla+b, decreased significantly, intercellular CO2 concentration and Chla/Chlb increased, and net photosynthetic rate were dropped.2.5 Under nitrate stress, the leaves of sweet pepper seedlings optical system response reduced the maximum energy conversion efficiency central, close degree of increased electron transfer blocked, a large number of acceptor side quinone receptor accumulation, leaves absorb too much energy led to inactivation of PSⅡreaction centers, photosynthetic apparatus damage, PSⅡreaction center performance index PIABS,PICS significantly reduced, thus weakening the leaf photosynthesis rate.3 Effects of diatomaceous organic fertilizers on some physiological metabolism of sweet pepper seedlings under nitrate stress3.1 After diatomaceous organic fertilizer manuring into the soil, the soil conductivity, soil salinity and NO₃- levels of soil were reduced, and soil organic matter content was significantly increased, and the impact of sweet pepper seedlings under nitrate stress have been alleviated and plant height, stem diameter and fresh weight has improved significantly.3.2 Application of diatomaceous earth organic fertilizer significantly reduced O2·- producing rate, and H₂O₂ content; effectively alleviate the damage being caused by active oxygen on lipid membranes ,and manifested as MDA content decreased, membrane permeability decreased.3.3 Application of diatomaceous organic fertilizer significantly increased the content of Chla, Chlb, Chla+b, stomatal conductance, leaf transpiration rate, and photosynthesis rate of sweet pepper seedlings.3.4 Diatomaceous organic fertilizer could alleviate the damage of PSⅡof sweet pepper seedlings under nitrate stress, and manifested as Fv/Fm increased, the closure level of PSⅡactive reaction center decreased, and the electronic transmission of PSⅡreaction center and PSⅡperformance index increased significantly.