# Evidence of plasticity in Triodanis perfoliata: differential flowering response to interannual spring temperature and variation across North America

## TL;DR

This study shows that the flowering time of Triodanis perfoliata varies with spring temperature and that this sensitivity differs across its geographic range in North America.

## Contribution

The paper reveals differential phenological plasticity in T. perfoliata populations in response to interannual temperature variation.

## Key findings

- Flowering time in T. perfoliata correlates with interannual spring temperature, with warmer springs leading to earlier flowering.
- Populations in cooler, higher latitude regions show less sensitivity to temperature variation than those in warmer, lower latitude regions.
- The findings suggest adaptive or plastic responses to local climate and highlight the importance of intraspecific variation in phenological studies.

## Abstract

Examining long-term trends in climate-driven flowering time shifts provides valuable insights, but can mask dynamic interannual variation that may reveal the capacity for short-term phenological responses. We examined the interannual and intraspecific dynamics of flowering time shifts in Triodanis perfoliata (Campanulaceae) using a comprehensive dataset with a total 1493 vetted records spanning 1895–2022 across the contiguous USA. Here, we build on previous work demonstrating long-term flowering time advances (Berg et al., An examination of climate-driven flowering-time shifts at large spatial scales over 153 years in a common weedy annual. Am J Bot 2019;106:1435–43.). Specifically, we examined the influence of interannual temperature variation on flowering time, and explored how these responses varied across a broad geographic range. We found a significant correlation between interannual spring temperature variation and flowering time, with cooler springs associated with delayed flowering and warmer springs associated with earlier flowering. Critically, we found that the magnitude of this relationship varied among T. perfoliata populations, with individuals in cooler, higher latitude regions showing less sensitivity to interannual temperature variation than those in warmer, lower latitude regions. This differential sensitivity suggests potential adaptive or plastic responses to local climatic conditions and may have implications for gene flow and the long-term ecological and evolutionary trajectory of T. perfoliata populations. This study highlights the importance of considering both long-term trends and interannual variation in phenological research, and emphasizes the need for further investigation into the drivers and consequences of intraspecific variation in phenological sensitivity.

Shifts in flowering time driven by increases in temperature have been documented across a range of flowering plant species. However, intraspecific dynamics of flowering time responses to interannual changes in temperature elucidate the potential for rapid phenological responses. We examine such relationships in a widespread spring flowering annual and show a direct relationship between flowering time and interannual variation in temperature. Further, we demonstrate a spatial pattern in which the sensitivity of these phenological responses varies in relationship to historical local temperatures. In general these data emphasize the importance of exploring phenological trends intraspecifically and across geographic ranges.