The long-term response of photosynthesis in walnut (Juglans regia L.) leaf to a leaf-to-fruit ratio

For clarifying the relationship between a leaf-to-fruit ratio (LFR) and photosynthesis, LFR manipulation was performed with Juglans regia cv. Xinxin2 in order to test the photosynthesis response to LFR in source leaves. Results showed that LFR with one and two leaves was positively correlated with net photosynthetic rate (P-N), chlorophyll content, and specific leaf mass, implying extremely low LFR inhibited the leaf development. However, LFR with five leaves was negatively correlated with P-N, positively correlated with starch, but not related to intercellular CO2 concentration, indicating the high LFR caused the nonstomatal limitation and feedback inhibition of photosynthetic production. No significant differences in P-N between LFRs (with three and four leaves) probably indicated a balanced state of coordinated supply and demand between the source leaf and sink fruit. The above results indicated that the response of photosynthesis in the source leaves to LFR depends on the variation range of LFR.