Heat tolerance of tropical herbaceous plants increases with elevation

Background and Aims

Tropical plants are assumed to be especially vulnerable to global warming because their physiologies are adapted to relatively constant temperatures throughout the year. Furthermore, it has been found that woody plants in colder high elevation environments are less tolerant to high temperatures than plants in the warmer lowlands. Here, we examined heat tolerance in a group of herbaceous plants with a wide elevational distribution in the tropics.

Methods

This study focused on 61 species from the order Zingiberales (ginger and banana-like plants) distributed from the lowlands (50 m asl) to lower montane forests (2000 m asl) along the Barva elevational gradient in Costa Rica.

This study addressed the following questions: a) Does heat tolerance of Zingiberales species differ along the elevational gradient? b) Does heat tolerance vary along the elevational gradient within families of Zingiberales? c) Does heat tolerance vary along the elevational gradient within species for those with broad elevational distributions? To test if the temperature that causes damage to the function of photosystem II (PSII) in Zingiberales is associated with the temperatures prevalent at their elevation, we estimated heat tolerance (T ₅₀ ) of PSII using chlorophyll fluorescence techniques.

Key Results

In contrast to the results found in tropical trees, our results showed that T ₅₀ is higher at higher elevations than in the lowlands for herbaceous plants species. This trend was observed across plant communities and families, and within most species with wide distributions along the elevational gradient.

Conclusions

Our study suggests that herbs differ from trees in their elevational patterns in heat tolerance. We hypothesize that maximum and minimum leaf temperatures, and UV radiation may play a role in the observed pattern.