| Tomato (Lycopersiconesculentum Mill.) belongs to the family Solanaceae, and is one of the most widely grown, productive and consumed vegetables in the world. As soilless cultivation can be easy to precisely control nutrients in the solution and provide a possible solution to continuous cropping obstacle in soil-based systems while both increased yield and improved quality of fruit, it has become an important planting pattern to grow tomatoes. Conventional hydroponic cultivation often results in rot of the roots because of the lower dissolved oxygen levels in the nutritional solutions. Aeroponics is a new soilless culture technique through intermittently spraying with the atomized nutrient solution to meet the demands of vegetable growth, and can effectively solve the problems of root rot in conventional hydroponics systems. It shows an extremely broad application prospect in tomato production. Nitrogen and potassium are two of the largest necessary nutrient elements tomato needed. Accordingly, the nutrition managements of nitrogen and potassium are key agronomic strategies to improve the yield and nutritional quality of tomato. Previous studies have investigated the effects of application of nitrogen (N), potassium (K) and nitrogen form on the yield and the quality of vegetables in hydroponics systems. However, the interaction effects of N and K on yield and antioxidant nutritional qualities of different tomato cultivars in aeroponic cultivation were rarely reported. It is the key technology to coordinate and solve the problems of cost-yield-quality in aeroponics systems by exploring the nitrogen and potassium nutrient in nutritional solution. The objective of this study is to select appropriate aeroponic nutrient formular, and then to investigate the interaction effects of nitrogen, potassium nutrient and nitrogen form on the yield, antioxidant contents and antioxidant activity, and to determine the optimal nutrient solution management for aeroponically grown tomato, which would provide scientific basis for the production of vegetables with high yield and nutritional quality. The main results obtained from the experiments are summarized as follows:1. The effects of five hydroponic nutrient solutions, Holland formula, Shandong Agricultural University formula, Japanese Yamazaki formula, England Hewitt formula and Japanese Garden formula on the seedlings growth, photosynthesis and nutrients absorption of aeroponically grown two tomato(Lycopersicon esculentum Mill.) cultivars, Dwarf-red (D-red) and Dwarf-yellow (D-yellow), were compared. The results showed that the two tomato seedlings grown in NS4had the highest dry biomass, plant height, stem diameter, root length, root activity, SPAD value and photosynthetic index, including net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2concentration, but lowest in Shandong Agricultural University formula. The highest total nitrogen content and total potassium content were observed in England Hewitt formula, and the lowest were in Shandong Agricultural University formula. The D-red had the highest root volume in England Hewitt formula, but the D-yellow in Japanese Yamazaki formula, and both had the lowest root volumes in Shandong Agricultural University formula. The D-red had the higher plant height, stem diameter, root length, root activity and nitrogen use efficiency and potassium use efficiency than those of the D-yellow. Root volume and total potassium content in the D-yellow were higher than those in the D-red.These results indicated that aeroponically grown tomato seedlings in England Hewitt formula solution produced high dry biomass, photosynthetic index, nitrogen use efficiency and potassium use efficiency, suggesting that England Hewitt formula solution is the most ideal nutrient solution for aeroponically grown tomato seedling than other formula solutions, whereas Shandong Agricultural University formula solution is unsuitable, In all, dry biomass and quality were both higher in the D-red compared with the D-yellow.2. An aeroponics was carried out to study the effects of different nitrogen levels (2,12and22mmol/L) and potassium levels (4and8mmol/L) on the growth of seedling and fruit yield, nutritional quality of two tomato (Lycopersicon esculentum Mill.) cultivars, Dwarf-red (D-red) and Dwarf-yellow (D-yellow). Our results showed that plant height, leaf area, root activity, root morphological values (total root length, root surface area and root volume) and dry biomass of both two tomato cultivars seedlings significantly increased with the increasing nitrogen level from2mmol/L to12mmol/L, but decreased when further increased up to22mmol/L. The SPAD value, photosynthetic index(net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2concentration), total nitrogen content and total potassium content significantly increased while stem diameter and nitrogen use efficiency decreased and potassium use efficiency decreased with nitrogen levels increasing. When potassium level increased from4mmol/L to8mmol/L at N2and N12level, the plant height, leaf area, SPAD value, photosynthetic index, root activity, root morphological values, total nitrogen content and total potassium content increased while potassium use efficiency decreased, but had no significant difference in the stem diameter. Root activity, dry biomass, nitrogen use efficiency and potassium use efficiency were higher in the D-red compared with those in the D-yellow, but total potassium content was opposite.The results also showed that fruit size, fruit rate, yield, the content of soluble sugar, soluble solids, carotenoids, β-carotene, lycopene, DPPH radical scavenging rates and ABTS value (both Hydro-and Lipo-antioxidant activity) increased with increasing N level from2mmol/L to12mmol/L, then decreased significantly when N level increased up to22mmol/L. The contents of titratable acidity and nitrate increased as N level increased in the nutrient solution. The contents of ascorbic acid, flavonoids and total phenolic declined with increasing N level. Besides, the fruit yield, favor quality, antioxidant accumulation and antioxidant activity were enhanced by increasing application of K from4mmol/L to8mmol/L, however, the nitrate content declined. Higher fruit yield, antioxidant accumulation and antioxidant activity were found in the D-red compared with those in the D-yellow. Overall, our results suggested that12mmol/L N and8mmol/L K may be suitable for tomato cultivation in aeroponic system, which not only increased the fruit yield, but also improved the nutrition quality, and D-red should be a better cultivar for aeroponic cultivation compared with the D-yellow.3. An aeroponics was conducted to investigate the effects of two potassium levels (4and8mmol/L) and different NO3-:NH4+ratios (100:0,75:25,50:50,25:75) on the growth of tomato seedlings, nutritional quality and antioxidant activity in tomato fruit, and two tomato (Lycopersicon esculentum Mill.) cultivars, Dwarf-red (D-red) and Dwarf-yellow (D-yellow), were used in this study. Results showed that under the same potassium level, the plant height, stem diameter, leaf area, SPAD value, photosynthetic index (net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2concentration), water use efficiency, root activity, root morphological values (total root length, root surface area and root volume), dry biomass, total nitrogen content, nitrogen use efficiency and potassium use efficiency increased and then decreased gradually with increasing ammonium concentrations in the nutrient solution, and total potassium content and NO3--N content decreased while NH4+-N content increased gradually in aeroponically grown tomato seedlings. Furthermore, when potassium level was increased from4mmol/L to8mmol/L under the same NO3-:NH4+ratio except the ratio was25:75, the leaf area, SPAD values, root activity, dry biomass, total potassium content, NO3--N content, nitrogen use efficiency increased, while NH4+-N content decreased. And potassium use efficiency declined in NO3-:NH4+ratio was50:50and25:75when potassium level was increased. The plant height, stem diameter, root activity, dry biomass, total potassium content and potassium use efficiency were significantly higher in the D-red while water use efficiency was lower than those in the D-yellow.The fruit size, fruit rate, fruit yield, the contents of soluble sugar, soluble solids, ascorbic acid, flavonoids, total phenolic, carotenoids, β-carotene and lycopene, DPPH radical scavenging rates and the ABTS value (both Hydro-and Lipo-antioxidant activity) of fruit were all increased when the proportion of ammonium increased up to25%or50%, and then decreased. The titratable acidity increased, while the content of nitrate decreased with increasing the proportion of ammonium in nutrient solution, In addition, the increasing of K level from4mmol/L to8mmol/L increased the fruit rate, fruit size, fruit yield, the contents of soluble sugar, soluble solids, antioxidant accumulation and antioxidant activity, but decreased the content of nitrate, and had no significant difference on the titratable acidity. In all treatments, the D-red had greater fruit yield, higher contents of antioxidant compounds, and stronger antioxidant activity than the D-yellow. Hence NO3-:NH4+ratio of75:25should be optimal for the aeroponically grown tomato. The D-red should be a better cultivar for aeroponic cultivation compared with the D-yellow. |
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