Genome size exhibits extensive variation across the life of tree. Previous studies have predominantly focused on interspecific comparisons. However, the ecological drivers and adaptive implications of the variation, particularly within a single species, have received less attention.

In a study published in Physiologia Plantarum, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences investigated the intraspecific genome size variation and its role in ecological adaptation in the hexaploid plant Rorippa indica (R. indica). The findings showed that plants can adapt to tropical environments by significantly enlarging their genomes.

Researchers conducted a comprehensive study on 952 individuals from 97 different populations of R. indica. By integrating flow cytometry, plastome-based phylogeography, repetitive sequence analysis, and reciprocal transplant experiments, they investigated natural patterns of genome size variation and adaptive mechanisms in the plants.

A continuous range of genome sizes was identified within R. indica, which correlated closely with geography, climatic gradients and lineage history. Tropical lineages of R. indica consistently possessed larger genomes compared to their temperate counterparts. Genome expansion was found to be primarily driven by the amplification of specific sequences including 45S rDNA and Ty1 retrotransposons.

A critical common garden experiment provided the functional evidence. Plant strains with different genome sizes were transplanted to both Xishuangbanna (tropical) and Kunming (temperate) sites. It was found that in the stable, warm tropical environment of Xishuangbanna, the large-genome strains produced significantly more seeds, showing a clear adaptive advantage.

This study provides insights into how genome size interacts with the environment. It suggests that under global warming, species or populations with larger genomes might be favored due to their increased reproductive output. "Genomic expansion appears to be a positive response to the relatively stable conditions of the tropics," said Prof. XING Yaowu from XTBG.