Variation in nitrogen uptake and utilization efficiency in spinach genotypes and its evaluation

Nitrogen(N)is an essential element for both crop development and yield,however,excessive application of N fertilizer not only increases the production cost but also causes environmental pollution.Therefore,there is an urgent need to improve nitrogen use efficiency(NUE)and minimize N losses for the development of sustainable agricultural systems.Numerous studies showed that NUE may be improved by N management strategies but this approach needed a lot of input.It is therefore critical to select and cultivate crops with enhanced NUE.Previous studies on NUE were mainly focused on crops,such as rice,wheat,barley,canola,however researches on vegetables were rather limited,even though over-fertilization was prevalent nowadays in vegetable production in China.The aim of this study was to investigate genotypic differences in growth traits and NUE in spinach(Spinach oleracea L.) grown under N-deficient and N-sufficient conditions in hydroponic cultivation.Dry matter,N accumulation,N usage index,N uptake and utilization efficiency were measured and compared for 30spinach genotypes grown under N-deficient(2 mmol / L) and N-sufficient(10 mmol / L) conditions by hydroponic experiment.The results showed significant differences in all parameters of NUE among the spinach genotypes under Ndeficient and N-sufficient conditions.At the higher N level,plants produced higher shoot dry masses,N concentrations,N accumulation and N uptake efficiency,but lower N utilization efficiency and N utilization ratios.The shoot dry mass may be used as a critical index for evaluating the difference in NUE in spinach genotypes at the same N level because of high co-efficiency of variation at low and high N levels.In addition,shoot N accumulation,N uptake efficiency and N utilization ratio also showed high co-efficiency of variation,and exhibited a significant positive correlation with shoot dry mass.Efficient and inefficient genotypes were selected based on the criterion of producing more or less than 10%shoot dry mass,respectively,at low and high N levels.The typical efficient spinach genotypes exhibited larger shoot dry masses,and higher N uptake efficiency,N utilization efficiency and N utilization ratio than the inefficient genotypes under low and high N conditions.The path coefficient analysis revealed that NUE was dominated by N uptake efficiency,while N utilization efficiency also had some contribution to NUE at the two different N levels.In sum,significant differences in NUE are found among 30spinach genotypes and it is feasible to select Nefficient spinach genotypes from the existing varieties.The shoot dry mass,which can be easily measured,can be used as a simple and effective parameter for NUE,whereas shoot N accumulation,N uptake efficiency and N utilization ratio can also be employed as secondary indices for selection and evaluation of NUE in spinach.N uptake efficiency and utilization efficiency both influence NUE of spinach.Thus,improvements in N uptake efficiency and N utilization efficiency may be valuable to breed N-efficient spinach genotypes under conditions of either low or high N availability.