Nitrogen fixation characteristics of root nodules in different peanut varieties and their relationship with yield

Root nodules in peanut (Arachis hypogaea L.) could directly utilize nitrogen (N) in the atmosphere as N source, which plays an important role in the N supply in peanut. However, little is known about the mechanism of efficient N fixation by root nodule. In this study, ¹⁵N tracer technology was used to investigate the characteristics of N fixation by root nodule and its relationship with peanut yields of 19 varieties in a pot culture experiment. Results showed that there were significant differences in nodule number, fresh quality, internal material, N fixation amount and other related indices among different varieties. The range of number and fresh mass of root nodule was 170.59-696.15 per pot and 0.83-3.74 g per pot, with coefficients of variation (CV) of 36.1% and 41.1%, respectively. The range of leghaemoglobin content and nitrogenase activity was 15.51-23.23 mg per pot and 2.75-20.46 μmol C₂H₄·h^-1 per pot, with CV of 13.1% and 57.2%, respectively. The CV of nitrogenase activity was significantly higher than that of leghaemoglobin content, indicating that nitrogenase activity was not only affected by leghaemoglobin content but also other factors. The range of N fixation by root nodule and total N accumulation was 0.71-1.82 and 2.16-3.72 g per pot, with CV of 21.6% and 12.9%, respectively. The CV of the former was significantly higher than that of the latter, indicating that other N sources could automatically compensate the deficit when N fixation of root nodule was insufficient. Nitrogen fixation by root nodule was one of the main N sources for peanut, while the average N supply percentage was more than 40% of the total N, with a maximum of 50%. Cultivating the variety with high N supply capacity is an effective way for N-saving cultivation in the peanut production. Except for nodule number, there were significantly positive correlations between the other indices and peanut yield, indicating that the physiological indicators of N fixation were closely related to N fixation capacity by root nodule and the final yield. Therefore, enhancing these characters would help achieve high yield of peanut and simultaneously reduce fertilizer application.