| Abstract:In order to clarify the effects of different nitrogen levels on the root development and above-ground growth of Lycium barbarum, and to explore the correlation between root morphological characteristics and the yield and quality of Lycium barbarum fruit, the four-year-old plant of the main cultivar of Lycium barbarum ‘Ningqi No.7’ was used as the test material, a field experiment was conducted to study the effects of different nitrogen fertilizer application rates N1 (20% nitrogen reduction, 540 kg·hm-2), N2 (medium nitrogen, 675 kg·hm-2), N3(nitrogen increase 20%,810 kg·hm-2) on the root morphology, root cumulative growth and aboveground leaf nitrogen content, SPAD value, net photosynthetic rate, economic yield, and fruit quality of Lycium barbarum during the summer growth period.The results showed that: (1) Under different nitrogen application levels, besides the average root diameter of the root morphological characteristics of Lycium barbarum root system, the total root length, total root projected area, total root surface area, and root volume all increased first and then decreased with the increase of nitrogen application rate.That is , the root growth under N3 treatment was inhibited to a certain extent, resulting in the cumulative increase of root length N2 (1 778.1 cm)>N3(1 342.2 cm)>N1(1 330.4 cm) from large to small, respectively.(2) Different nitrogen application rates had an impact on the distribution of roots in the soil. The results showed that under N1 and N2 treatments,the increments of Lycium barbarum roots were mainly distributed in the 20-60 cm soil layer;under N3 treatments,the increment of Lycium barbarum roots were mainly distributed in the 0-20 cm soil layer, indicating that high nitrogen conditions would affect the longitudinal extension of the root system in the soil layer, and would lead to unreasonable vertical root distribution in the long term.(3) In the above ground part, increasing application of nitrogen fertilizer promoted the significant increase of leaf nitrogen content and SPAD value (P＜0.05), and the net photosynthetic rate showed a trend of increase at first and then trend of decrease;fruit yield, Lycium barbarum polysaccharides, total flavonoids and β-carotene were not significantly different from each other under different treatments(P>0.05). Only the vertical and horizontal diameter of the fresh fruit, the total sugar and betaine content of the fruit were significantly affected by different nitrogen application rates ( P<0.05).(4) The principal component analysis method was used for comprehensive evaluation, and the scores were N2 (2.386)> N3 (0.105)> N1 (-2.491) from high to low,that is,medium nitrogen fertilization was most beneficial to the growth and development of Lycium barbarum plants, and the stability of fruit yield and quality. (5) The correlation analysis of the aboveground and underground indexes showed that the average root diameter and the leaf nitrogen content and SPAD value had a significant negative correlation (P＜0.05); the root volume and the fruit betaine content had significantly positive correlation (P<0.05).In summary, the medium-nitrogen treatment with a fertilizer rate of 675 kg·hm-2 not only can promote the growth and development of Lycium barbarum root system and the establish a good root architecture of the four-year ‘Ningqi No.7’ plant, but also can play a good role in plant photosynthesis and fruit quality and efficiency improvement of Lycium barbarum.The results of the study provide data support for the scientific nitrogen application of the main Lycium barbarum varieties in northwestern China, and also provide a reference basis for regulating the growth and development of Lycium barbarum plants aboveground and underground through cultivation measures. |
