Increasing nitrogen supply to phosphorus-deficient Medicago sativa decreases shoot growth and enhances root exudation of tartrate to discharge surplus carbon dependent on nitrogen form

• Published in: Plant and soil Vol. 469; no. 1/2; pp. 193 - 211
• Main Authors: He, Honghua, Zhang, Zekun, Peng, Qi, Chang, Chao, Su, Rui, Cheng, Xiao, Li, Yingxin, Pang, Jiayin, Du, Sheng, Lambers, Hans
• Format: Journal Article
• Language: English
• Published: Cham Springer Science + Business Media 01.12.2021; Springer International Publishing; Springer; Springer Nature B.V
• Subjects: Agriculture; Alfalfa; Analysis; biomass; Biomedical and Life Sciences; Carbon; Discharge; Ecology; Exudation; greenhouse experimentation; Growth; Identification and classification; Life Sciences; Medicago sativa; Methods; Nitrogen; nitrogen content; Phosphorus; Plant growth; plant nitrogen content; Plant Physiology; Plant Sciences; Plant-soil relationships; Regular Article; REGULAR ARTICLES; Roots; Shoots (Botany); soil; Soil Science & Conservation; Soils; Australia; China; Alfalfa; Biomass allocation; Fertilisation; Carboxylate release; Nutritional status; Nitrogen to phosphorus ratio
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-021-05161-y

Aims Carboxylate release by roots has been considered a strategy for mobilisation and acquisition of phosphorus (P). However, recently, it was argued that carboxylate release may be a way to discharge surplus carbon produced under conditions that limit plant growth. Plant P status may not be the main factor driving carboxylate release by roots. Instead, plant nitrogen (N) status and/or N:P ratio of the soil or plant may play a more important role in enhancing carboxylate release. Methods A greenhouse pot experiment was performed to grow alfalfa in a P-deficient soil, supplied with two rates of P (0 and 20 mg kg −1 ) in combination with four forms of nitrogen (N) at five rates (0, 25, 50, 75, and 100 mg kg −1 ), to explore the effects of P rate, N form, N rate, and their interactions on plant growth, P and N status, and carboxylate release, and to determine the factors driving carboxylate release. Results Nitrogen addition weakened the positive effect of P addition on plant growth, and increased plant N and P concentrations; P addition increased plant P concentration, but weakened the effect of N addition on plant N concentration. The amount of tartrate increased dramatically with increasing N rate, which decreased shoot growth, depending on N form. At high P supply, tartrate exudation correlated negatively with shoot biomass. Conclusions Nitrogen addition to P-deficient alfalfa decreased shoot growth and enhanced the release of tartrate, likely to discharge surplus carbon; and the effects varied with N form.