Abstract
Drought stress reduces cereal crop growth and yield due to modifications to interactions between sink and source. However, little research has investigated multiple carbon sources and their relationships with sink capacities, especially in response to drought stress at different growth stages. The objective of this study was thus to examine two major carbon sources (i.e., photosynthetic assimilation in the flag leaf and remobilisation of pre‐anthesis reserves in stems) and their interactions with sink strength in response to drought stress at different phenological stages. A greenhouse experiment was conducted at five water regimes: well‐watered (WW), progressive drought (PD), and drought stress (DS) during vegetative growth (DS‐V), early reproductive growth (DS‐ER), and post‐anthesis (DS‐PA). Compared with the WW regime, the DS‐V treatment reduced shoot biomass, grain yield, number of grains per pot, grain weight, harvest index, and water‐soluble carbohydrates in stems despite the recovered photosynthesis after rehydration. Wheat plants subject to DS‐PA exhibited reduced shoot biomass, grain yield, grain weight, and post‐anthesis photosynthetic rate but greater depletion of water‐soluble carbohydrates in stems during grain filling relative to the WW regime. Grain yield positively correlated with residual water‐soluble carbohydrates in stems and late‐season photosynthetic rates. This study demonstrated yield losses associated with changes in sink and source capacities in response to drought stress at different phenological stages and showcased the predominant role of the two carbon sources in grain filling.