Abstract
Understanding the contributions of source-sink relationships to photosynthesis will help achieve high wheat grain yields. A single-factor field experiment was conducted to quantify the regulatory effects of different sink-source ratios on wheat photosynthetic characteristics, including two wheat cultivars with different source-sink relationships as materials for detailed source-sink manipulations through flag leaf removal (LR) and removal of spikelets on one side of each spike (SR). Compared with a control (CK), LR increased the sink-source ratio (23.84%) and significantly reduced the yield (16.17%), 1000-kernel weight (11.73%), and kernels per spike (7.33%). LR increased the leaves' net photosynthetic rate (Pn) (4.27-15.82%), the electron transfer rate (3.97-14.93%), and the Rubisco activity (2.16-12.25%) in the short term, and LR increased sucrose synthesis-related enzyme activities (3.96-19.95%) and gene expressions (SPS1, SUS1, CIN1, and SUT1). Compared with CK, SR reduced the sink-source ratio (44.12%) and significantly increased the 1000-kernel weight (10.02%) but reduced the yield (43.93%) and kernels per spike (49.31%). SR reduced the leaves' Pn (8.54-21.41%), the electron transfer rate (3.51-16.71%), and the Rubisco activity (5.96-21.51%), and the photosynthetic process was limited. SR decreased sucrose synthesis-related enzyme activities (5.12-29.09%) and gene expressions (SPS1, SUS1, CIN1, and SUT1). Therefore, a higher sink-source ratio is an important indicator of high photosynthetic efficiency, which can be used as a screening and judgment index in variety selection and cultivation regulation.