Limitations in Grain Yield and Carbon Partitioning Differs in Soybean (Glycine max (L.) Merr.) Cultivars with Contrasting Photosynthetic Phosphorus-Use Efficiency

The aim of the work was to elucidate how different P doses alter photosynthesis and to identify their effects on carbon partitioning and grain production in two soybean cultivars with contrasting photosynthetic phosphorus-use efficiency (PPUE). Two cultivars, UFVS80B10 and TMG7063, were subjected to increasing doses of phosphorus (0.01 mM, 0.1 mM, 0.5 mM, and 1 mM) in Hoagland nutrient solutions. The cultivar with a higher PPUE (TMG7063), presented 24%, 25%, 41%, 46%, and 31% of net photosynthetic rate, stomatal conductance, maximum carboxylation rate of rubisco, electron transport, and triose phosphate use, respectively, than the UFVS80B10 cultivar. However, in both cultivars, there was a reduction in those variables due to the lower P content in the tissues of plants subjected to P deficit. The P deficit caused damage to photosystem II (PSII) only when the plants were close to the R6 stage. The cultivars were efficient in dissipating nonphotochemical energy during P deficit (0.01 mM), but with higher photochemical efficiency in the cultivar TMG7063 at the reproductive stage in higher P doses. The higher absorption of P in the cultivar with low PPUE reflected higher starch and sugar contents in the leaves, stems, and roots, causing a greater biomass gain but with grain yield of 45% lower than the cultivar with the highest PPUE. A higher PPUE in soybean is associated with the maintenance in carbohydrate partitioning under low P, maximizing grain production and presenting photoprotective mechanisms mainly in the grain filling stage.

Automated summary

The aim of this study was to investigate the effects of different phosphorus doses on soybean photosynthesis and carbon partitioning. The results showed that soybean cultivars with higher photosynthetic phosphorus-use efficiency (PPUE) had higher net photosynthetic rate, stomatal conductance, carboxylation rate, electron transport, and triose phosphate use. However, these variables were reduced due to lower phosphorus content in plant tissues under phosphorus deficit. Damage to photosystem II (PSII) only occurred when soybean plants were close to the reproductive stage. The cultivars were efficient in dissipating nonphotochemical energy during phosphorus deficit, but showed higher photochemical efficiency at the reproductive stage with higher phosphorus doses. The soybean cultivar with low PPUE absorbed more phosphorus, resulting in higher starch and sugar contents and greater biomass gain, but lower grain yield compared to the cultivar with the highest PPUE.