Stomatal distribution and post-fire recovery: Intra- and interspecific variation in plants of the pyrogenic Florida scrub.

Premise: Amphistomy, the presence of stomata on both leaf surfaces, can increase photosynthesis yet is uncommon across vascular plants. The relative infrequency of amphistomy is often attributed to high costs, such as transpirational water loss. The Florida scrub-a hot, dry, shrub-dominated habitat-historically has experienced frequent fire, yet decades of anthropogenic suppression coupled with the reintroduction of prescribed burns has led to varied fire regimes. In this study, we investigated the links between amphistomy and fire with regard to the presence of the trait across species in this pyrogenic habitat and within-species variation before and after experimental fire and across a time-since-fire gradient (0.25-50 years).

Methods: We surveyed the presence of amphistomy for 116 plant species across scrub habitats and experimentally investigated intraspecific variation in stomatal traits for two amphistomatous, post-fire resprouting species of palmetto, Serenoa repens and Sabal etonia (Arecaceae).

Results: Amphistomy was present in 62.9% of all surveyed species and 85.7% of post-fire obligate reseeders, suggesting amphistomy may be particularly beneficial in this group and broadly in the Florida scrub conditions. The stomatal ratio (upper/total stomatal density) was generally stable within and across individuals of both species after fire. Stomatal density decreased following fire in S. etonia, with both species experiencing high variation in the post-fire years.

Conclusions: Amphistomy is common in the Florida scrub and relatively stable within species in response to fire, while stomatal density responds plastically during post-fire recovery.