Dynamic effects of irrigation on photosynthesis and yield-related physiological characteristics in different glutinous wheat cultivars

Water scarcity critically constrains wheat production in North China, yet the irrigation responsiveness of novel glutinous wheat cultivars remains poorly quantified. This study systematically investigated the physiological mechanisms of common wheat Shimai 19 (SM19), partially glutinous SM19-P (Wx-B1 null), and fully glutinous SM19-N (triple null) under three irrigation regimes: rain-fed (W0), water-saving (W1: jointing irrigation), and conventional irrigation (W2: overwintering + jointing + flowering irrigations). Dynamic monitoring of flag leaf photosynthesis (Soil Plant Analysis Development (SPAD), stomatal conductance (Gs), transpiration rate (Tr), net photosynthetic rate (Pn)), antioxidant enzyme systems (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) net photosynthetic rate (Pn), malondialdehyde (MDA)), grain starch synthase activities (granule-bound starch synthase (GBSS), soluble starch synthase (SSS), adenosine diphosphate glucose pyrophosphorylase (AGPase), starch branching enzyme (SBE)), and yield components revealed that: (1) SM19 achieved maximum photosynthetic capacity under W1 (Pn increased by 59.54% <i>vs.</i> W0 at 21 days post anthesis (DPA), <i>p</i> < 0.05) with optimal oxidative damage resistance (MDA reduced by 78.73% at 0 DPA), whereas SM19-P and SM19-N required W2 to reach photosynthetic peaks (Pn increased by 60.56% in SM19-P) and enzyme activity maxima (CAT increased by 66.67% in SM19-N). (2) Starch synthase activities peaked under water deficit (W0) early in grain-filling (≤14 DPA) but became tightly coupled to irrigation frequency thereafter. This was supported by a highly significant correlation between irrigation and final yield (<i>r</i> = 0.803, <i>p</i> < 0.01). The coordinated upregulation of AGPase and SSS (<i>r</i> = 0.726, <i>p</i> < 0.01) underpinned this response. The superior branched-starch accumulation in genotype SM19-N (+23%) was linked to its markedly higher SBE activity (<i>r</i> = 0.867, <i>p</i> < 0.01). (3) Yield optimization was genotype-specific: SM19 yielded highest under W1, while SM19-N peaked under W2. The study demonstrates that, unlike common wheat (SM19) which performs optimally under water-saving irrigation, the novel glutinous lines (SM19-P/SM19-N) require full irrigation to realize their yield potential, highlighting a critical trade-off between starch quality and drought adaptation. The key indicators identified-photosynthetic efficiency, antioxidant capacity, and starch metabolism-provide a theoretical foundation for developing future glutinous wheat varieties combining drought tolerance with high starch quality.