Source–sink characterization, classification and responses to nitrogen in different wheat cultivars

Optimizing source-sink dynamics is fundamental to understanding crop yield formation and achieving high productivity. This study aims to elucidate the physiological mechanisms by which source-sink traits influence wheat yield and to classify cultivars based on their limiting factors. Field experiments were conducted using three wheat cultivars (YM1, YM25, and ZM27) under two nitrogen (N) application rates to assess their source-sink characteristics. Compared with YM1, the cultivars YM25 and ZM27 exhibited significantly enhanced source capacity, characterized by larger leaf area, higher specific leaf weight (SLW), extended SPAD duration, and photosynthetic duration. Consequently, YM25 and ZM27 achieved significantly higher grain yields and sink capacities. The yield advantage was primarily driven by an increased number of kernels per spikelet and higher 1000-kernel weight (TKW), which resulted from a faster grain-filling rate, earlier onset of peak filling, and improved grain fullness. In contrast, YM1 displayed limited source strength (smaller leaf area, lower SLW) and poor sink activity, characterized by slower grain filling and reduced grain weight. Source-sink classification analysis revealed that YM25 and ZM27 are source-limited cultivars, possessing high source and sink strengths but a relatively high sink-source ratio. Conversely, YM1 is a sink-limited cultivar, exhibiting low source and sink strengths with a relatively low sink-source ratio. Furthermore, N fertilization effectively regulated source-sink relationships, specifically by mitigating source limitations in high-yielding cultivars. These findings provide a theoretical basis for cultivating high-yield wheat varieties by coordinating source-sink interactions.