Studies on improving phosphorus use efficiency of potato: effects on plant growth, physiology, and quality of tubers

Abstract

Plants develop different strategies in response to low and high P supply. Potato has a low P use efficiency (PUE) compared to other crops, which is caused by its limited root system. Therefore, it is necessary to gain more knowledge of the morphological and physiological processes associated with P deficiency and toxicity in potato, as well as to explore an alternative approach to ameliorate the P-deficient conditions. This dissertation aimed to characterize plant growth, physiology, and tuber quality of potato as influenced by cultivar, P availability, and PGPR. The results revealed a reduction in plant height and biomass by 60–80% under P deficiency compared to P optimum. P deficiency and toxicity conditions also altered the mineral concentration and allocation in plants due to nutrient imbalance. The stress induced by both—P deficiency and toxicity—was evident from an accumulation of proline and secondary metabolites. Furthermore, root metabolite profiling revealed that P deficiency reduced concentrations of sugars and organic acids by 20-90%, but increased amino acids concentrations by 1.5-14.8 times. However, the effect of P toxicity on metabolic changes in roots was less pronounced. These responses were also different between the cultivars. We found the capability of Milva to allocate biomass, P, and sugars to roots under low P supply, causing high P uptake and PUE. In contrast, Lady Claire was not efficient in P uptake under low P levels, but this cultivar was more efficient in P uptake under high P availability. Total P uptake of both cultivars was influenced by modifications of root morphology, which was controlled by P, sugar, and indole-3-acetic acid concentrations in roots. A further comprehensive comparison of six potato cultivars also showed a contrasting response of P-efficient and P-inefficient cultivars under low P availability. P-efficient cultivars—Agria, Milva, and Lilly—possessed substantial plant biomass, tuber yield, and high P uptake efficiency under low P supply. The P-inefficient cultivars—Lady Claire, Sieglinde, and Verdi—lacked the ability to form tubers under P deprivation, as well as the ability to efficiently uptake of P at low P level, but they were efficient in P uptake at high soil P levels. Improved PUpE was important for plant tolerance under limited P availability, allowing efficient use of the supplied P. Although PUtE was impaired under P deficiency, plants attempted to maintain ions and osmolytes in leaves, which are necessary for plants to adapt to the stress caused by P deficiency and mobilize leaf inorganic phosphate to increase internal PUE and photosynthesis. The reduction of plant biomass and tuber yield under P deficiency could be caused by the lower CO2 assimilation. Furthermore, P deficiency significantly decreased tuber yield, dry matter, and starch concentrations in Agria, Milva, and Lilly. Nevertheless, contents of protein, sugars, and minerals in tubers, as well as antioxidant capacity were enhanced under this condition in these cultivars. To ameliorate P deficiency, the inoculation of five diverse PGPR strains as well as Bacillus subtilis addition enhanced root morphology, P uptake, and PUE. Additionally, Bacillus subtilis also upregulated P transporter genes (StPHT1;1 and StPHT2;1) in young leaves. These results highlight the important traits and strategies contributing to potato plant tolerance under P deficiency and toxicity and indicate an opportunity to improve P efficiency and tuber quality of potato under deficient conditions by choosing more efficient cultivars.