Agronomic and physiological traits associated with genetic improvement of phosphorus use efficiency of wheat grown in a purple lithomorphic soil

Developing wheat that acquires and uses phosphorus (P) more efficiently is a promising and low-cost solution for increasing grain yield and reducing P-related environmental impacts. The present study identified agronomic and physiological traits that contribute to genetic variation in the P acquisition, remobilization, and utilization efficiency of 11 wheat cultivars from southwest China grown in P-deficient purple lithomorphic soil (Olsen P = 4.7) with balanced (75 kg P ha−1) and excess P (120 kg P ha−1) supplies. On average, soil P deficiency (–P) reduced root P uptake (17.0%–60.8%), P remobilization (33.9%–52.8%), dry mass yield (11.5%–39.2%), and grain yield (17.7%–54.4%). Balanced P (+P) increased grain yield via increased plant biomass rather than increased HI. –P increased phosphorus uptake efficiency (PUpE, 4.5-fold), phosphorus utilization efficiency (PUtE, 1.25-fold), and phosphorus use efficiency (PUE, 5.4-fold) compared with those under +P, and PUtE explained most (58.1%–60.8%) of the genetic variation in PUE under both –P and +P. The high root P uptake of P-efficient cultivars under –P was regulated by root surface area and root length density in the 0–10 cm soil layer but not in the 10–20 and 20–40 cm soil layers, suggesting that a topsoil foraging strategy is a more economical approach than deeper root exploration for increasing P uptake. Root P uptake before anthesis and P remobilization after anthesis were critical for increasing the PUtE of wheat, given that P-efficient cultivars showed higher Pn (net photosynthetic rate) and sucrose levels than P-inefficient cultivars. Pn reduction by –P resulted from decreased Gs and Ci, and high evapotranspiration under +P increased shoot P% by increasing root P uptake. Genetic variation in the source-to-sink ratio was observed in consequence of a +P-induced allometric increase in sucrose in leaves and kernels. Owing to these beneficial effects, +P increased the kernel N and P yields of the 11 cultivars by 9.9%–52.4% and 12.3%–48.8%, respectively. The findings of this study could help improve wheat in future breeding efforts and P management by identifying desirable P-efficient phenotypes in P-deficient farming systems.