Functional traits can explain coordinated seedling responses to drought and freezing stress

Limited plant establishment creates demographic bottlenecks that can alter vegetation trajectories in changing environments, yet it is unclear how common eco-evolutionary indicators of plant strategy shape early response to key stressors.

We evaluated how early functional traits, phylogeny, and adult climate niche jointly explain seedling drought and freezing tolerance across 49 semi-arid rangeland species.

The best models explained 36% of variation in freezing tolerance (traits only) and 45% of variation in drought tolerance (traits, phylogeny, and climate), identifying both shared and unique indicators of different stress responses.

Drought tolerance was explained by rapid root elongation and large seed size, while phylogeny captured additional tolerance within the grass family. Seedling freezing tolerance was linked to rapid root elongation and colder thresholds for root growth, though traits shared some explanatory power with adult climate niche (cold temperature distribution).

While stress resistance can be shaped by phylogeny and adaptations to long-term climate regimes, our results elucidate early traits with clearer direct links to establishment capacity under drought and freezing stress, across species. Additional research is needed to understand how variation in stress response strategies across multiple demographic stages (e.g., seeds, seedlings, mature plant) and ecological scales (e.g., within and across species' climate distributions) could affect vegetation distributions and trajectories in changing environments.