Enhancement of rhizosphere citric acid and decrease of NO3−/NH4+ ratio by root interactions facilitate N fixation and transfer

• Published in: Plant and soil Vol. 447; no. 1-2; pp. 169 - 182
• Main Authors: Wang, Xinyu, Gao, Yingzhi, Zhang, Hualiang, Shao, Zeqiang, Sun, Baoru, Gao, Qiang
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.02.2020; Springer Nature B.V
• Subjects: Acids; Agricultural practices; Alfalfa; Biomedical and Life Sciences; Citric acid; Competition; Corn; Depletion; Ecology; Fixation; Greenhouse effect; Greenhouses; Intercropping; Life Sciences; Monoculture; Nitrates; Nitrogen; Nodulation; Nodules; Nutrients; Organic acids; Plant Physiology; Plant Sciences; Regular Article; Rhizosphere; Soil Science & Conservation; NO; N fixation; Intercropping; NH; N transfer; Citric acid; N uptake; ratio
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-018-03918-6

Aims Cereal can stimulate legume N fixation through competition for soil mineral N. In addition, organic acids in the rhizosphere can mobilize external nutrients, which may help nodulation. However, how much NO 3 − and NH 4 + competition and organic acids in the rhizosphere of intercropped crops contribute to N fixation remains unclear and requires study. Methods Field and greenhouse experiments were conducted to quantify effects of N competition and organic acids on N fixation in a maize/alfalfa intercropping system. Results Intercropping increased nitrogen derived from the atmosphere (%Ndfa), nodules number, and leghemoglobin content by 43.66%, 85.53%, 141.05%, respectively, leading to significantly improved total N uptake and yield, compared to monoculture. The improved %Ndfa was not only due to the depletion of NO 3 − , but also significantly correlated with the decrease of NO 3 − /NH 4 + ratio and the increase of citric acid in rhizosphere of alfalfa, which could mobilize soluble resources for N fixation under no N addition. Overall, 15.4%–21.5% of N fixed by alfalfa was transferred to associated maize, and the improved N fixation enhanced N transfer. Conclusions Our findings provide a mechanism for how root interactions facilitate N fixation, highlighting the importance of NO 3 − /NH 4 + ratio and citric acid in nutrient mobilization for N fixation.