Higher Photochemical Quenching and Better Maintenance of Carbon Dioxide Fixation Are Key Traits for Phosphorus Use...

Maintaining carbohydrate biosynthesis and C assimilation is critical under phosphorus (P) deficiency as inorganic P (Pi) is essential for ATP synthesis. Low available P in agricultural soils occurs worldwide and fertilizer P sources are being depleted. Thus, identifying biosynthetic traits that are favorable for P use efficiency (PUE) in crops is crucial. This study characterized agronomic traits, gas exchange, and chlorophyll traits of two wheat genotypes that differ in PUE. RAC875 was a P efficient genotype and Wyalkatchem was a P inefficient genotype. The plants were grown in pots under growth room conditions at two P levels; 10 mg P kg^-1 soil (low P) and 30 mg P kg^-1 soil (adequate P) and gas exchange and chlorophyll fluorescence were measured at the vegetative and booting stages using a portable photosynthesis system (LI-6800, LI-COR, United States). Results showed significant differences in some agronomic traits between the two wheat genotypes, i.e., greater leaf size and area, and a higher ratio of productive tillers to total tillers in RC875 when compared with Wyalkatchem. The CO₂ response curve showed Wyalkatchem was more severely affected by low P than RAC875 at the booting stage. The relative ratio of the photosynthetic rate at low P to adequate P was also higher in RAC875 at the booting stage. Photochemical quenching (qP) in RAC875 was significantly higher when compared with Wyalkatchem at the booting stage. Maintaining CO₂ fixation capacity under low P and higher qP would be associated with P efficiency in RAC875 and measuring qP could be a potential method to screen for P efficient wheat.