Leaf morphology-δ13C synergy in drought response and G×E interactions in Toona sinensis

Toona sinensis is prized for its superior wood quality, ranking among the most important timber species. However, its growth and development has been severely constrained by persistent drought stress, which has become more frequent due to global climate change. Therefore, elucidating its drought response mechanisms and breeding high-yield, drought-resistant varieties are crucial for mitigating plantation productivity losses caused by global climate change. This study analyzed the effects of genotypic (G), environmental (E), and genotype-by-environment (G×E) interactions on the growth, leaf morphology, anatomy, and δ 13 C of T. sinensis clones in three test sites. We evaluated the key traits associated with drought response, and investigated the relationship between growth and drought resistance. The results revealed significant genotypic and G×E effects on volume. Leaf phenotypic variation was primarily determined by G×E effects, though leaf thickness and δ13C exhibited significant genotypic effects. In severely water-deficient regions, clone volume significantly decreased, leaf area reduced, leaf thickness increased, and δ13C markedly rose. Among leaf-related traits, δ13C was identified as a key indicator of drought response, with its increase mainly attributed to enhanced leaf thickness due to palisade tissue thickening. Regression analysis showed no significant correlation between the comprehensive drought resistance index (based on leaf phenotypes) and volume. Thus, clones were evaluated separately across three test sites. On the basis of high volume, potentially drought-resistant clones were further screened (XC10-4 and XC15-3 for XT; XC6-17 and XC30-2 for HZ; XC15-3 and XC6-13 for LA), all achieving genetic gains in volume exceeding 20%. These findings provide practical insights for the sustainable development of future T. sinensis plantations.