Abstract
The changes in physiological properties and leaf ultrastructures caused by early nitrogen application for potatoes under drought stress were explored. Potato variety Chuanyu117 was used to conduct a controlled experiment in a sand medium. Nutrient solution treatments (0.84, 1.26, 1.68 and 2.10) were administered, followed by severe drought, moderate drought, and normal (control) water treatments (45, 60, and 75% of soil saturation moisture capacity) in the seedling stage of potatoes. Early additional nitrogen application maintained chlorophyll content in potato leaves under drought stress and increased activities of protective enzymes in the plants. Severe and moderate drought stress treatments resulted in the smallest reductions in chlorophyll content compared with the control and largest increases in POD and CAT activities. Under the same water conditions, potato with high nitrogen treatment (1.68 g N L-1) had significantly higher net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and intercellular CO2 concentration (Ci) than other nitrogen treatment levels; the highest levels of these photosynthetic parameters were obtained under the normal water condition. As drought stress increased, the degree of damage to chloroplasts and mitochondria in potato leaves gradually increased and the number of starch grains increased; however, with increases in the nitrogen application level, the degree of damage to chloroplasts and mitochondria gradually decreased. Early additional nitrogen application had mitigative effects on the damage to cellular structures of potato leaves under drought stress and could improve gas exchange and increase absorption and utilization of light energy in potato leaves. Further, the adaptive capacity of photosynthetic structures in potato leaves increased, leading to greater drought resistance in potato. However, with increases in the nitrogen levels, drought resistance of potato showed an initially increasing trend that decreased subsequently, suggesting that over-application of nitrogen reduced drought resistance in potato. Key words: Early nitrogen application, drought stress, physiological properties, photosynthetic parameters, ultrastructure.
Highlights
China is the world's largest potato-producing country and launched the "Potato as a Staple Food" strategy in 2015, whereby over 50% of potatoes produced were expected to be consumed as a staple food by 2020 and theZheng et al 251 planting area of potato would gradually increase annually
Through an examination of the influence of early nitrogen application on physiological properties and ultrastructures of potato leaves under drought stress, this study aimed to reveal the mechanism underlying the improvement in the drought resistance of the potato plants through early nitrogen application, so as to provide a theoretical basis for China's drought resistant potato cultivation
Influence of early nitrogen application on chlorophyll content of potato leaves under drought stress in the seedling stage
Summary
China is the world's largest potato-producing country and launched the "Potato as a Staple Food" strategy in 2015, whereby over 50% of potatoes produced were expected to be consumed as a staple food by 2020 and theZheng et al 251 planting area of potato would gradually increase annually. 60% of China's potato planting area is in arid or semi-arid regions, drought stress is severely restricting China's potato production and the development of the potato industry (Xu et al, 2011). Nitrogen is associated with plant growth and yield and plays an important role in regulating crop growth and development under stress (Saneoka et al, 2004). Under different soil water supply conditions, it is still unclear whether nitrogen nutritional status affecting growth and photosynthetic physiological responses of plants is associated with cell structure damage. China's major potato planting regions often experience early stage (seedling stage) drought, which causes poor growth that seriously affects tuber yield in the late stage, while the relationship among early nitrogen application, photosynthesis, ultrastructures, and drought resistance of potatoes still needs to be investigated further
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