Effects Of Different NO₃^--N/NH₄⁺-N Ratios On Cucumber Growth, Nitrogen Uptake And Metabolism Under Suboptimal Temperature And Light Intensity

Long term suboptimal temperature（15¹8 ℃/10¹2 ℃） and light intensity（165³00 μmol·m-2·s-1） are two of the major factors which caused cucumber disorders of the physiological metabolism and inhibition of growth, and effected cucumber yield and quality in greenhouse during winter and early spring. Nitrogen（N） is an essential macronutrient that exerts the greatest influence on plant growth and plays a significant role in improving yield and quality. The inorganic ions（NO3--N and NH4+-N）available to plants are another vital for plant growth. To investigate effects of NO₃^--N/NH₄⁺-N on cucumber growth, physiological characteristics and early yield under suboptimal temperature and light intensity, using cucumber “zhongnong 26” as material, three NO₃^--N/NH₄⁺-N ratios, 26:2, 21:7 and14:14, were applied as treatments under normal environmental conditions（25/15 ℃, 600 ± 20μmol·m-2·s-1） and suboptimal environmental conditions（18 ℃ /10 ℃, 180 ± 20 μmol·m-2·s-1）.Cucumber seedlings at the two-true leaves were treated, and ten days after moving the seedlings to the phytotron which provides the condition of suboptimal temperature and light, the dry weight,root architecture and the activities of nitrogen metabolism enzymes were tested. Furthermore, seedlings at initial flowering stage were treated to study the early yield. The main research results are as follows:1、The biomass and pigment content of cucumber seedlings grown under suboptimal environmental conditions were decreased significantly. NO3–-N/NH4+-N=21:7-fed plants had the highest DW and pigment content under normal and suboptimal environmental conditions.2 、 The content of nitrate was significantly reduced by suboptimal environmental conditions, while ammonium content was significantly increased. NO3–-N/NH4+-N=21:7 significantly increased total nitrogen content in suboptimal and normal environmental conditions. In addition, the content of P、K、Ca、Mg、Fe and Mn were decreased and the content of Cu and Zn were raised first and then decreased when the proportion of NO3– was decreased.3、The root activity and root architecture of plants under normal environmental conditions were higher than those grown under suboptimal environmental conditions. NO₃^--N/NH₄⁺-N=21:7-fed plants under suboptimal environmental conditions had the longest total root length, the biggest root volume and root surface area and the largest number of root tips, and significantly increased activity of H+-ATPase. The genes of most NRT and AMT were upregulated.4 、 The activities of NR and GOGAT of plants grown under suboptimal environmental conditions were in line with plants under normal environmental conditions, while the GS activity was significantly increased. The activities of NR, GS and GOGAT of plants treated by NO₃^--N/NH₄⁺-N=21:7 were higher and upregulated NR, GLN and GLU.5、NO₃^--N/NH₄⁺-N=21:7 can significantly increase early yield of cucumber, which provided technical guidance for regulating the ratios of NO₃^--N/NH₄⁺-N to increase cucumber yield under suboptimal environmental conditions.