Abstract: To investigate the regulatory mechanism of transplanting date on leaf development of Yunyan 87 tobacco in Shaowu tobacco-growing area of Fujian Province, and to clarify the quantitative contributions of key meteorological factors, thereby providing theoretical support for optimizing the transplanting date in this region, an experiment was conducted in 2024 with four transplanting date treatments (February 28, March 8, March 18, and March 28). The changes in middle-leaf morphology, anatomical structure, and cell wall cellulose and lignin contents at the squaring stage were analyzed. Correlation analysis and hierarchical decomposition were performed in combination with meteorological data, including temperature, precipitation, and solar radiation during the growth period. The results showed that the Y3 treatment (transplanted on March 18) exhibited superior leaf morphology and structure, characterized by a broad-rounded leaf shape, the largest palisade cell area, appropriate levels of palisade-to-spongy tissue ratio (P/S) and palisade-to-leaf ratio (CTR) and leaf area not significantly different from the optimal treatment (Y2) but significantly higher than that in the too-early or too-late transplanting treatments. Premature transplanting led to insufficient leaf expansion and narrow leaves; delayed transplanting resulted in an obvious increase in spongy tissue thickness and an obvious decrease in P/S and CTR. Contribution rate analysis of meteorological factors indicated that air temperature was the key factor regulating leaf thickness, solar radiation primarily regulated palisade tissue density and the P/S ratio, while precipitation was the dominant factor with the highest comprehensive contribution, mainly regulating palisade tissue porosity and spongy tissue thickness. Under the ecological conditions of the Shaowu tobacco-growing area, transplanting in mid-March optimized the synchronization of the tobacco growth period with light, temperature, and water resources, facilitating the formation of leaf structures with coordinated palisade and spongy tissues and balanced cell wall components. This laid a structural foundation for mitigating early-stage waterlogging stress and resisting late-stage high-temperature and drought stress, making it a suitable transplanting date for producing high-quality tobacco leaves.

Key words: transplanting period, Yunyan 87, leaf anatomical structure, palisade tissue, spongy mesophyll, meteorological factor, cultivation regulation