The role of ecological niche and seed mass in macroevolution of germination tolerance to salinity

The limited understanding of how early life-history transitions respond to changing environmental conditions constrains our knowledge of climate change impacts. Soil salinity intensification is a significant global issue, yet the eco-evolutionary aspects of germination responses to salinity gradients remain understudied.

We employed phylogenetic comparative methods, utilizing a century of published records and data on germination responses to salinity gradient, ecological niches and seed traits, to test hypotheses on the variation and evolution of germination tolerance to salinity across 327 plant species. We related germination salinity tolerance to growth forms, lifespans and biomes to examine potential eco-evolutionary factors underlying germination responses to a salinity gradient.

Our results reveal significant variation in germination salinity tolerance among different growth forms, lifespans and biomes. Germination salinity tolerance parameters are evolutionarily labile and environmental conditions predominantly drive germination tolerance to salinity gradients by stabilizing selection. Ecological niche and seed traits, such as seed mass and embryo length, significantly mediate germination responses to salinity.

This first quantitative assessment of the evolutionary tempo and mode of germination salinity tolerance across diverse plant taxa provides novel insights into how evolutionary processes shape stress tolerance during germination, emphasizing the role of seed mass and growth forms in driving salinity tolerance to germination. These findings enhance our understanding of the strategies plants employ to navigate salinity stress.