Under supplementary irrigation, phosphorus fertilizer input enhances post-anthesis dry matter accumulation and yield by improving canopy characteristics

Context
While post-anthesis dry matter accumulation (DMAA) is crucial for wheat yield, few studies have systematically examined how canopy photosynthesis at different leaf positions responds to water and phosphorus management.
Objective
The aim of this study was to quantify the effects of different irrigation and phosphorus levels on wheat canopy traits and DMAA dynamics and to analyze how the photosynthetic traits of different canopy leaf positions drive DMAA and yield.
Methods
A three-year field experiment with a split-plot design was conducted. Irrigation levels ranged from 70% to 100% relative water content, and phosphorus rates varied from 0 to 180 kg P₂O₅ ha⁻¹ . Canopy characteristics (e.g., leaf area index, net photosynthetic rate) and DMAA dynamics were measured.
Results
Water-phosphorus coupling significantly changes canopy structure and function. The leaf area index of each leaf layer increased, and the increase of the leaves below the third leaf was the largest. The chlorophyll content, net photosynthetic rate, antioxidant enzyme activity and post-anthesis dry matter accumulation related parameters of the top three leaves showed a consistent trend, reaching the peak under the specific water and phosphorus combination. The P2 treatment under low irrigation conditions and the P1 treatment under medium and high irrigation conditions reached the peak under the specific water and phosphorus combination. Multivariate analysis showed that canopy traits, especially the related indexes of the second leaf, directly drove dry matter accumulation and yield formation after anthesis. When the relative water content was 85% and the phosphorus application rate was 60–120 kg ha−1, the wheat yield reached the maximum.
Conclusions
Moderate irrigation (85% relative water content) combined with reduced phosphorus input (60 kg ha⁻¹) optimized canopy structure, delayed senescence, enhanced photosynthetic capacity, and ultimately increased grain yield through improved DMAA.
Implications
This study provides a physiological basis for optimizing water and phosphorus management to enhance canopy performance and productivity in wheat cultivation.