Regulated deficit irrigation was associated with altered stem hormones and carbon metabolism that improved yield and lodging-related traits in drip-irrigated spring wheat

Water scarcity is becoming increasingly severe, while the demand for stable and high-yield wheat production continues to rise. Under these circumstances, achieving the dual objectives of water conservation and yield enhancement through precise water management represents a critical challenge for sustainable agriculture, particularly in arid oasis regions.In this study, we investigated the dynamics of endogenous hormones and carbon metabolism in the basal first and second internodes (I1 and I2) of wheat stems under drip irrigation conditions. Special attention was given to the roles of non-structural carbohydrates (NSC) and structural carbohydrates (SC) in regulating stem development. The objective was to elucidate how variations in hormonal regulation and carbon allocation contribute to improvements in wheat grain yield as well as stem lodging-related traits. Two wheat cultivars differing in water sensitivity (XC6 and XC22) were assigned to the main plots. Subplots were subjected to regulated deficit irrigation at two stages (tillering, T and jointing, J) with two levels of water: mild deficit (60-65% FC, FC is field water holding capacity, T1, J1) and moderate deficit (45-50% FC, T2, J2). Following the completion of deficit irrigation, we rehydrated to 75-80% FC. A fully irrigated treatment (75-80% FC, CK) served as the control. Relationships among these physiological indicators, yield components, and stem lodging-related traits were analyzed. The results showed that the T1 treatment significantly enhanced endogenous hormone concentrations and hormonal ratios (gibberellins, GA; zeatin + zeatin riboside, Z + ZR; gibberellin/indole-3-acetic acid, GA/IAA, and zeatin + zeatin riboside/abscisic acid, (Z + ZR)/ABA). Moreover, T1 markedly stimulated the activities of key enzymes involved in sucrose and fructan metabolism, thereby promoting the accumulation of NSC in wheat stems. Consequently, T1 promoted greater grain yield (1.79%-14.01%). In addition, T1 achieved the highest productivity while maintaining superior water-saving efficiency. The endogenous hormones of I1 and the promotion of NSC metabolism were more effective. In contrast, the J1 treatment predominantly activated enzymes associated with lignin biosynthesis and cellulose synthesis, thereby promoting the deposition of SC in the stems. This process significantly enhanced stems filling degree and breaking strength (28.12%-164.86%). And the strengthening effect was more pronounced in I1 than in I2. XC6 exhibited superior hormonal balance, carbon metabolic capacity, and lodging-related stem properties compared with XC22. Correlation and variable importance in projection (VIP) analyzed further revealed that grain number per spike, thousand-kernel weight, gibberellin (GA) in both basal internodes (I1 and I2) and sucrose fructosyltransferase (SST) activity, the hormonal ratio (Z + ZR)/ABA of I1 were the major contributors to yield formation. In contrast, sucrose content (Suc) in both I1 and I2, along with cinnamyl alcohol dehydrogenase (CAD), phenylalanine ammonia-lyase (PAL), and cellulose content (CC) in I1 had the greatest influence on stem filling degree and breaking strength. Overall, the T1 treatment enhanced endogenous hormone accumulation, improved hormonal coordination. And T1 also enhanced stems NSC metabolism. These led to increase yield. In contrast, the J1 was linked to improved stem lodging-related traits, corresponding to increased lignin and cellulose metabolism. Collectively, these findings provide a physiological basis for achieving both water conservation and high yield in wheat production through precise irrigation management in arid oasis regions.