Research Of Different Nutrient Solutions On Cucumber Seedlings Under Suboptimal Temperature

In northern China, cucumber seedlings are often subjected to suboptimal temperature（15/8 ℃） stress during spring or winter. Under such environment, the seedlings cultured with standard nutrient solution become weak and its leaves become yellow. So it is very important to study the nutrient solution under suboptimal temperature. This study aimed to relieve the adverse effects of suboptimal temperature environment on cucumber seedlings by adjusted Magnesium（Mg）and Potassium（K） concentration in the nutrient solution. By using a climatic chamber（25/18℃ day/night or 15/8℃ day/night）, cucumber ‘Bo Nai 3000’ were cultured with a standard Yamazaki cucumber nutrient solution or a nutrient solution changed concentration of K⁺and Mg²⁺. Hypothermia under different nutrient solution formula of cucumber seedling growth and development were studied, the effects of photosynthetic fluorescence characteristics and nutrient uptake and distribution of, for the winter and spring of cucumber seedlings of nutrient solution management provide theoretical basis and technical support. The main results are as follows:1. Effects of magnesium and potassium on the growth of cucumber seedlings under suboptimal temperature indicated: Appropriate increased the Mg²⁺ concentration can significantly improve seedling index of cucumber seedlings under suboptimal temperature. When Mg²⁺ and K⁺ concentration were 6 mmol/L, the seedling index had a maximum value 0.17.The effects of Magnesium and potassium on root morphology were different. K⁺ concentration was positively correlated with total root length and root surface area. But Mg²⁺ was positively correlated with the average diameter of the root system. To cucumber of 0-0.5 mm diameter growth, a higher proportion of the minerals related to K⁺, the increase of total root length and total volume, and significantly inhibited the growth of 0.5-1.0 mm and greater than 1.0 mm.2. Effects of magnesium and potassium on dry matter accumulation and distribution of cucumber seedlings under suboptimal temperature indicated: Compared to normal temperature, the dry biomass of stems and leaves decreased while the root dry biomass increased under suboptimal temperature. Under low K concentration, root and stem dry biomass increased with Mg²⁺ concentration increased. The high Mg²⁺concentration of nutrient solution contributed to the distribution of dry matter to leaf.3. Effects of magnesium and potassium on mineral elements absorption and distribution of cucumber seedlings under suboptimal temperature indicated: Under suboptimal temperature in leaves of cucumber seedlings in N, P, K, Ca, Mg and Fe contents decreased except for Fe,5 kinds of nutrient absorption and distribution proportion was leaf > stem > root, leaf elements distribution ratio between 50%-80%, stem at 20%-30%, root accounted for 10%-20%, and Fe in root, stem and leaf allocation ratio of leaf > root > stem. The content of N and P in the roots and leaves was the lowest, the content of K was the lowest in the leaves, Ca and Mg were the highest in the stem, and the content of Fe was highest in the root. Mg²⁺ and K⁺ affect the absorption of elements together, when the concentration is low, the performance is synergistic.4. The absorption amount of N was positively correlated with Ca absorption and negatively correlated with Mg, K and Ca, Ca and Mg as well as K and Mg were negatively correlated, K and Ca reached significant levels, K and Mg, Ca and Mg all reached very significant level. N and Ca were significantly positively correlated with Chl（a+b） and Pn, and the amount of Mg absorption was not significantly related to Pn, but the relationship between and total chlorophyll was not significant.5. Effects of different nutrient solution on photosynthesis and Chlorophyll fluorescence characteristics of cucumber seedlings under suboptimal temperature indicated: Under suboptimal temperature reduced chlorophyll content, Chl a/b increased, by speeding up the energy transfer speed way to adapt to the sub low temperature stress and non stomatal limitation factors caused the decrease of PN, the fluorescence yield decreased for increasing heat dissipation of energy. Increasing the amount of Mg²⁺ and K⁺ in the nutrient solution can increase the chlorophyll content, while the two restrict each other to affect the photosynthesis. Improve the nutrient solution of Mg²⁺ and Pn, Tr, FV ’/ fm’, q P and PS II increased first and then decreased, high K⁺ is not conducive to cucumber net photosynthesis rate and transpiration rate. When Mg²⁺ is 4-6mmol/L in the nutrient solution, K⁺ is 6mmol/L, Ca2+ is 3.5-7mmol/L, NO3- is 14-28mmol/L and Fe2+ is 0.1mmol/L it has a good effect on photosynthesis and photosynthetic apparatus.To sum up, when the nutrient solution concentration of Mg²⁺4-6mmol/L, concentration of K⁺ 6mmol/L,Ca2+concentration 3.5-7mmol/L, NO3-for 14-28mmol/L and Fe2 + as 0.1 mmol/L and other ion concentration in the standard nutrient solution concentration unchanged, the strong seedling index of cucumber seedlings, root morphology, dry matter accumulation and potassium and magnesium comprehensive effect better performance. It can effectively resist the adverse effects of suboptimal temperature on cucumber seedlings.