Description:
Nitrogen (N) is essential for crop growth and development under stress. The photosynthetic capacity of crops depends on the leaf N content (Na ), and leaf N allocation is an important factor affecting net photosynthetic rate (Pn ). However, the relationship between N supply and leaf N allocation and the effects of different N forms on cucumber growth at low-temperature stress are still unclear. In this study, the effects of different N concentrations (NC) and ammonium (NH4+ )-nitrate (NO3− ) ratios (A-NR) supplied to grown low-temperature-stressed cucumber at seedling and flowering to early fruiting stages on growth, photosynthesis, N accumulation, and leaf N allocation were assessed. NC, A-NR, and their interactions significantly affected leaf area, Pn , chlorophyll content, and N accumulation at seedling and flowering to early fruiting stages. When the cucumber plants were grown in low-temperature environment, the maximum photochemical efficiency, leaf area, Pn , chlorophyll content, Na , water-soluble proteins N (Nw ), and N accumulations in various organs were the greatest. The content of sodium dodecyl sulfate (a detergent) soluble protein N (Ns ) was minimal when the NCs at the seedling and flowering to early fruiting stages were 10.5 and 28 mmol·L−1 , respectively, and the A-NRs were both 1:1. Correlation analysis showed that leaf area, Pn , chlorophyll content, and N accumulation could be improved by increasing Na and Nw or reducing Ns . This finding suggested that increasing NC and NH4+ nutrition could increase Na and Nw in leaves and reduce the content of Ns , thereby improving photosynthetic capacity to promote leaf growth and increasing cucumber low-temperature resistance