Effects of intercropping on growth and nitrate accumulation of lettuce in aeroponics

Abstract: This paper studied the effects of intercropping on growth index, photosynthetic indices, nitrate content and nitrate reductase activity of aeroponics lettuce, and analyzed the main factors of nitrate accumulation in aboveground part of lettuce combined with the changes of mineral element content in nutrient solution. The results show that the intercropping is beneficial to improve the fresh quality of aboveground part of lettuce plants and promote the expansion of lettuce leaves, and at the same time, increase the lettuce root morphological parameters. When the lettuce plants are cultured for 20 d, they enter the vigorous growth period, and at this time, the fresh quality of aboveground part, plant height and leaf area of lettuce plants are greatly improved. Intercropping increases the SPAD (soil plant analysis development) value, net photosynthetic rate, stomatal conductance and transpiration rate of lettuce plants, but it has no obviously regular effect on intercellular CO2 concentration of lettuce plants. With the development of aeroponics time, the SPAD value of lettuce plants increases at first and then decreases slowly, and its maximum value appears after 20 d, and at this time, the chlorophyll volume of leaves is the largest and the synthesis rate is the fastest, which further prove that lettuce plants are in the vigorous growth period at this time. The net photosynthetic rate, stomatal conductance and transpiration rate increase gradually, and the net photosynthetic rate of leaves is positively correlated with stomatal conductance and transpiration rate, and the correlation coefficients are 0.937 and 0.950 respectively, which is consistent with the research results of Zhang Meishan on the leaves of Panax quinquefolium. In the whole period of aeroponics, intercropping reduces nitrate content of aboveground part of lettuce plants in varying degrees and the nitrate content decreases firstly and then increases. After 20 d, nitrate content in aboveground part of lettuce is the lowest, and it is reduced by 16.57% compared with monoculture, which shows good intercropping advantage. And the change trend of nitrate reductase activity is opposite to that of nitrate content. The correlation between nitrate content of aboveground part of lettuce plants and fresh quality growth rate, nitrate reductase activity was analyzed, and the results show that the decrease of nitrate content in aboveground part of lettuce is mainly due to the increase of nitrate reductase activity. The relationship between nitrate reductase activity and the changes of mineral element content in nutrient solution is different. The correlation coefficients between nitrate reductase activity and nitrate nitrogen consumption and manganese consumption in nutrient solution are relatively larger, and they are 0.882 and 0.851 respectively, which shows that the nitrate nitrogen consumption and manganese consumption in nutrient solution have great influence on the nitrate reductase activity. From the significance, we can see that the correlation between nitrate reductase activity and nitrate nitrogen consumption in nutrient solution is significant. The results reveal the main factors of nitrate accumulation in aboveground part of lettuce in intercropping mode and provide a theoretical basis for the study of the interaction mechanism of lettuce and cherry radish in intercropping mode.