Small Genome Size Ensures Adaptive Flexibility for an Alpine Ginger

Understanding the proximate and ultimate causes of genome size variation has been the focus of considerable research. However, the extent and cause of intraspecific variation in genome size are debated and poorly understood. This study aimed to test the role of genome size in adaptation through variations in intraspecific genome size. Genome size was measured in 53 Roscoea tibetica populations from the Hengduan Mountains using flow cytometry. Stomatal size and density data were collected from wild and common garden populations. Associations among genome size, environmental factors, and stomatal traits were explored. We found that high genome size 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 variations in genome size. Stomatal traits measured in the wild were significantly correlated with genome size, but no such correlations were detected in the common garden. Populations in the common garden had larger stomatal sizes and lower stomatal densities. Populations with smaller genome size presented a larger degree of stomatal trait variation from the wild to the common garden. Our findings suggest that intraspecific genome size has undergone adaptive evolution driven by environmental stress. A smaller genome size is more advantageous for the alpine ginger to adapt to and thrive in changing alpine habitats.