The small genome size ensures adaptive flexibility for an alpine ginger

Understanding the proximate and ultimate causes of genome size (GS) variation is the focus of much research. However, the extent and causes of intraspecific variation in GS is debated and poorly understood. This study aims to test the large-genome constraint hypothesis through the variations of intraspecific GS. GS was measured in 53Roscoea tibeticapopulations from the Hengduan Mountains using flow cytometry. Stomatal size and density were collected from the wild populations and common garden populations. Associations between GS and environmental factors, stomatal traits were explored. We found that high GS variability was positively correlated with most environmental factors but negatively correlated with solar radiation during the growing season. The environment, rather than geography, significantly influenced the variations in GS. The stomatal traits measured in the wild were significantly correlated with GS, but no such correlations were detected in the common garden. Populations in the common garden have larger stomatal size and lower stomatal density. Populations with smaller GS present larger degree of stomatal traits variation from wild to common garden. Our findings suggests that intraspecific GS has experienced adaptive evolution driven by environmental stress and the evolution of intraspecific GS can be explained by the large-genome constraint hypothesis. Smaller GS is more advantageous to the alpine ginger to adapt to alpine habitat and thrive in changing habitat.