Studies On Secondary Salinization Of The Greenhouse Soil And Effects Of Soil Salt On Pepper Seedling

In recent years, the rapid development of facility agriculture, the planting area increased year by year, however unreasonable fertilization, cultivation management and so lead to the occurrence of soil salinization, resulting in increased vegetable pests and diseases, yield and quality decline, and even contaminated ground water. So, soil salinization has an impact on our facility agriculture, especially the main obstacle to sustainable agricultural development. Currently, research for soil salinization of facility agriculture and plant salt disability has made great progress, but more is focused on the NaCl and NaN03. In this study, based on a typical vegetable producting area in northern China-Chifeng City, Inner Mongolia Autonomous Region,the greenhouse soil was surveyed,tested and analyzed.KNO3,K2SO4 and mixed salt(1:1), the main salt of soil salinization caused,was designed to be 0(CK),50,100,150,200mmol/L 5 treatments to stress pepper cultivation "LiangJian" seedlings. The results are as follows:1. Salinity accumulation and their variation of greenhouse soil in Chifeng region in different cultivation years was reaseached as:Greenhouse soil salt content is always higher than the open field, and 0～5 cm of soil salt content was significantly higher than 5～20cm, and surface salt has accumulated significantly; In 4 main producting area, accumulation of soil salinity was the heaviest in NingCheng County, salinity content generally more than 1.0g/kg. Salt accumulation lowest in Hongshan Qu had not yet reached salinity standards;It was 5 years of greenhouse cultivation that average salinity in 0～20cm soil layer was the highest; Soil salinization caused by the salt ions existed regional differences.Soil salinity in NingCheng County was based anion SO42-, NO3-, cation Ca2+, correlation coefficients were 0.975 **,0.974 ** and 0.875 *. Yuanbaoshan of main SO42- and Ca2+ -based, correlation coefficients were 0.950 * and 0.991 **.2. KNO3,K2SO4 and mixed salt stress on plant growth:After 14d treatment with 150mmol/L and 200 mmol/L, pepper seedling plant height, root length, leaf number and biomass accumulation was significantly inhibited; 28d after treatment, the growth point of wilting, dying leaves, root browning, tend to die. Within a certain time, it was favoarable for growth of pepper seedlings by treatment of 50mmol/L of KNO3 and mixed salt, K2SO4 not.3. Salt stress on photosynthesis on pepper sepper seedlings:14d after salt stress, Pn, Ch1, Chla, Chlb, E, and WUE were reduced significantly, Ci increased significantly. From 150mmol/L beginning the photosynthetic parameters did not change significantly; Pn decrease was mainly attributed to limitation of stomatal limitation by treatment of 50mmol/L, while the high concentration of salt stress, non-stomatal factors.4. Salt stress on physiological and biochemical characteristics of pepper:With increasing concentration of salt, water content in shoot and root pepper seedling increased firstly and then decreased, and 200 mmol/L salt stress was abvioursly lower than CK; 50mmol/L salt treatment, proline, soluble sugar, MDA content and EC gradually increased, and the high salt stress increased significantly; SOD activity first decreased and then rose, and POD and CAT showed a decrease-increase-decrease.5. Stress on pepper seedlings nutrient content:14d after salt treatment, in nutrient elements of pepper seedlings there were some differences in content of N, KNO3 and the mixed salt stress, N content in leaf was lower after the rise, while SO42- inhibited pepper seedlings uptaking NO3-N; P, K content in leaf had the same trend, P first decreased and then increased, but always lower than CK.K showed a significant increase;High concentrations of nitrate stress, the presence of nitrite in pepper leaves can not to be checked, and 50mmol/L nitrate treated leaves Guinea nitrate content decreased significantly, but its N content was significantly positive correlation, the correlation coefficient 0.830 **; Low-salt treatment, P and soluble sugar content was significantly negatively correlated, K and soluble sugar content was positively correlated; High salt Stress, N content and soluble sugar content was significantly negatively correlated.6. Salt stress on pepper seedling anatomy and starch grain accumulation:14d after salt treatment of 200mmol/L, pepper seedling mesophyll palisade cells and the epidermal cells were significantly smaller, thinner leaves.Palisade tissue, spongy tissue cell gap becomes larger, cells loosely arranged irregular; With 50mmol/L K2SO4 treatment, a significant thickening of leaves, tightly packed palisade cells, spongy smaller cell gap.But with KNO3 and mixed salt treatment, leaf anatomy did not change significantly. With 200mmol/L high salt stress, chloroplast size and shape had changed, particularly K2SO4 stress, chloroplast swelling rounded, disorderly heaped in the mesophyll cells, but not closed to the cell wall. With 200mmol/L of high salt stress, size of starch grains changed in root and leaf, starch granules in leaves stained lighter than that of CK, starch grains were significantly smaller; KNO3 and mixed salt stress, root starch grains were significantly larger than the CK, while K2SO4 stress, root starch grain size did not change significantly.7. Salt stress on pepper seedlings conducing tisse antomy of impact:14d after treatment with 200mmol/L KNO3, K2SO4 and mixed salt, root, stem, leaf and vascular structure of pepper seedling marked changes. Differentiation of primary structure was accelerated at 0.5cm and 1.0cm from the root tip; The xylem conduits was significantly smaller diameter, wall thickening, and xylem microscopic area increased; Vein vascular area increased, and vascular mechanical tissue thicked above.8. Considered salt stress effects on the morphological index, photosynthesis, physiological and biochemical characteristics, nutrient absorption and anatomical structure, K2SO4 more inhibitied on pepper seedling growth than KNO3 and mixed salt, therefore, greenhouse soil SO42- harm should be attented.In summary, with the increase of salt concentration, inhibition on pepper seedlings was increasing. Pepper seedling growth of salt inhibition was Pn decrease,osmotic stress,membrane damage, mesophyll cell structural damage and other comprehensive the result of factors. But the plant itself is adapting salt stress by physiological and biochemical changes and microstructure changes.