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

Honghua He, Zekun Zhang, Qi Peng, Chao Chang, Rui Su, Xiao Cheng, Yingxin Li, Jiayin Pang, Sheng Du, Hans Lambers

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

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.

Original languageEnglish
Number of pages19
JournalPlant and Soil
DOIs
Publication statusE-pub ahead of print - 24 Sep 2021

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