Climate change regulates sugar and alkaloid contents in tobacco: Evidence from 15 years of large-scale observations

Global climate change profoundly disrupts crop carbon-nutrient stoichiometry, threatening the stability and usability of agricultural value chains. The synergistic effects of multi-dimensional environmental forcing on secondary metabolism remain poorly resolved across large-scale ecoregions. Leveraging an extensive 15-year dataset of 2802 field-sampled individuals across China’s five major ecoregions, we integrate meteorological data with panel regression models to quantify the interactive climatic drivers of tobacco leaf chemistry. Over the past 15 years, climate warming has universally suppressed sugar accumulation while promoting the enrichment of alkaloid compounds. Specifically, each 1 ℃ of warming drove an average 2.7% increase in alkaloids and a 2.3% decline in reducing sugars. Plant adaptive responses exhibited pronounced spatial divergence dictated by precipitation availability. In water-abundant humid ecoregions, temperature and radiation acted as the core drivers governing the accumulation of sugars and alkaloids, with solar radiation playing a pivotal role in alkaloid biosynthesis in the SW region. Conversely, in arid regions, precipitation emerged as the primary selective pressure driving fluctuations in leaf chemistry. However, once water constraints were alleviated via alternative sources such as irrigation, temperature re-emerged as the paramount regulatory driver. Furthermore, we identified that elevated solar radiation antagonizes and buffers warming-induced alkaloid surges, whereas supplementary precipitation effectively mitigates the heat-driven depletion of reducing sugars. Predictive modeling under future SSPs indicates that unmitigated warming will precipitate extreme biochemical disruptions, including a projected 40% alkaloid surge in the NE region and a decline of more than 15% in reducing sugar content in the HH region. These findings elucidate the granular sensitivities of leaf chemistry to concurrent climatic stressors, providing a critical theoretical framework for designing region-specific, climate-resilient agricultural strategies.