Strategies of organic acid production and exudation in response to low-phosphorus stress in Chinese fir genotypes differing in phosphorus-use efficiencies

Abstract

Plants with high P-use efficiency adapted more effectively via increased organic acid content in roots and root exudates than those with low P-use efficiency. Plants with high P-use efficiency also redistributed P in their tissues as an adaptive response, when organic acid exudation did not improve P-use efficiency. Increased organic acid exudation enables plants to cope with low-phosphorus (P) stress conditions. We aimed to clarify the variation in organic acid exudation strategies among different breeding genotypes presenting high-phosphorous (P) use efficiency. In this study, Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] seedlings differing in P-use efficiency were compared regarding low-molecular weight organic acid content in roots and root exudates under low-P stress conditions, and dry weight and P-use efficiency also were examined. Compared to the genotype characterized by low P-use efficiency (M24), passive low-P tolerance (M1) or active capture of soil P (M4) genotypes effectively increased organic acid content in roots and root exudates. Although M1 was more sensitive to low P than M4, the former exhibited a specific tolerance to low P. Accordingly, the production of organic acids was slower, and the resultant stress response was less effective in M1 than in M4. Organic acid exudation did not improve P-use efficiency, given the absence of insoluble P in the rhizosphere, but M1 and M4 redistributed P in the tissues as an adaptive response. M4 also increased the root/shoot ratio and allocated more assimilation to root system to enhance P acquisition under low-P condition. In conclusion, the studied genotypes revealed different organic acid exudation strategies. Plants with high P-use efficiency adapted more effectively than those with low P-use efficiency. Metabolic and energy-use adjustments by plant organs, which facilitate plants’ passive adaptation under P-stress, are important survival strategies that allow adaptation to low-P environments.