A Cross‐Climate Comparison of Molecular Phenology in Three Tropical and Temperate Trees

exhibited sporadic transcriptional shifts triggered by slight cooling events (minimum temperatures of 21°C-22°C), whereas the temperate species showed clear annual cycles characterized by winter-specific expression patterns. Mild temperature decline in the tropical tree triggered widespread down-regulation of photosynthesis-related genes and activation of stress-response and jasmonate-associated signaling pathways, suggesting coordinated responses even to mild temperature declines. Cross-species comparison of 3793 single-copy orthologs showed that the sensitivity to temperature and dynamic range of gene expression were substantially larger relative to the narrow dynamic range of temperature in the tropics, indicating amplified transcriptional responses per unit of temperature variation. Conversely, temperate species displayed broad but proportionate transcriptomic shifts that paralleled large seasonal temperature fluctuations. These results demonstrate that transcriptional sensitivity to temperature is exaggerated in tropical species and buffered in temperate ones, extending Janzen's climate variability hypothesis from physiological tolerance to its molecular basis.