Abstract:

To screen nitrogen-efficient varieties of alfalfa， the nitrogen utilization characteristics of 20 alfalfa （Medicago sativa） varieties at the seedling stage were analyzed in a hydroponic experiment. The 20 varieties were grown in modified nitrogen-free Hoagland-Arnon nutrient solution supplemented with nitrogen at a low level （N₂₀， 20 mg·L^-1） or a normal level （N₂₀₀， 200 mg·L^-1）. The growth traits， key nitrogen assimilation enzyme activities， and nitrogen use efficiency （NUE） of the alfalfa plants were analyzed. The growth parameters determined were plant height， biomass， root length， and root volume； the physiological indices were nitrate reductase （NR） and glutamine synthetase （GS） activities， as well as whole-plant nitrogen content， nitrogen accumulation， and NUE. Correlation analysis， multiple linear regression analysis， and the membership function method were used to compare the performance of the 20 varieties. We detected significant differences in nitrogen utilization characteristics among the 20 varieties. Under low nitrogen （N₂₀）， the NUE of alfalfa varieties ranged from 2.71% to 23.66%. The variety ‘Benchmark’ （MX13） exhibited higher biomass， well-developed roots， and stronger nitrogen assimilation capacity， while ‘Northern SLT’ （MX9） showed weaker growth performance and a lower nitrogen assimilation ability. Under normal nitrogen （N₂₀₀）， the NUE of the varieties ranged from 2.71% to 22.36%， with ‘Benchmark’ （MX13）， ‘Rock’ （MA16）， and ‘Knight 2’ （MX19） demonstrating significantly higher NUE compared with those of the other varieties （P<0.05）. Correlation analysis indicated that plant height， root length， and nitrate reductase activity were significantly positively correlated with nitrogen content. Multiple linear regression analysis revealed that NUE was significantly influenced by nitrate reductase activity and aboveground biomass. Using the membership function method for comprehensive evaluation， the varieties ‘ Xiongyue’ （MX2）， ‘Salt-Tolerant Star’ （MX5）， ‘Radak Star’ （MX7）， ‘Benchmark’ （MX13）， ‘Peru’ （MX14）， and ‘Knight 2’ （MX19） exhibited composite scores of >0.50 under both N₂₀ and N₂₀₀ conditions. In contrast， ‘Crown’ （MX3）， ‘Rock’ （MX16）， and ‘Reindeer’ （MX20） showed composite scores of >0.50 under N₂₀ but <0.50 under N₂₀₀. Based on the comprehensive analysis， one high NUE variety， four normal NUE varieties， 13 low NUE varieties， and two nitrogen-inefficient varieties were identified. These findings provide a theoretical foundation for breeding nitrogen-efficient alfalfa varieties and optimizing nitrogen fertilizer management in field production.

Key words: alfalfa, nitrogen use efficiency, screening, correlation analysis, membership function analysis