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 P_n (net photosynthetic rate) and sucrose levels than P-inefficient cultivars. P_n reduction by –P resulted from decreased G_s and C_i, 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.

The moisture-conserving effect of straw mulch-based no-tillage (SMNT) is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm. However, the mechanisms underlying the positive effect of SMNT on wheat tillering are not fully elucidated. A split-plot experiment was designed to investigate the combined effects of SMNT and cultivars on tillering of dryland wheat grown under both dry and favorable climates. Application of SMNT to a cultivar with 1–2 tillers exploited both tillering and kernel-number plasticity, increasing the mean grain yield by 20.5%. This increase was attributed primarily to an increased first-tiller emergence rate resulting from increased N uptake, leaf N content, and N remobilization from tillers to their grain. The second and third tillers, as transient sinks, contributed to the tiller survival rate, which depends on tiller leaf number. The increased total N uptake by SMNT also increased the dry mass yield of tillers and the C:N ratio, reducing the asymmetric competition between main stem and tillers. Owing to these beneficial effects, reduced mitogen-activated protein kinase (MAPK) and abscisic acid signals were observed under SMNT, whereas indole-3-acetic acid (IAA) signals and genes involved in DNA replication and mismatch repair were increased. These signals activated three critical transcription factors (the calmodulin-binding transcription activator, GRAS domain, and cysteine-2/histidine-2 family) and further increased rapid drought response and tiller maintenance after stem extension. Phenylpropanoid biosynthesis, sphingolipid biosynthesis, and galactose metabolism were most relevant to increased tillering under SMNT because of their critical role in drought response and lignin biosynthesis. Our results suggest that straw mulch-based no-tillage activates rapid drought response and improved wheat tillering by coordinating root N uptake, N remobilization, and asymmetric competition between main stem and tillers.