Leaf anatomy as evidence of water-use strategies in two seasonally dry Brazilian vegetations: a comparison of co-occurring species

Abstract

Water-use strategies, i.e., the ratio of carbon gain to water loss, reflect how efficiently a plant assimilates carbon minimizing water loss. Leaf anatomical traits are crucial in shaping these strategies. Here, we look at evidence of water-use strategies from assessing leaf anatomical traits in two co-occurring species from the Cerrado (Brazilian savanna) and the Caatinga (a seasonally dry tropical forest in Brazil). We tested whether these species exhibit convergent anatomical adaptation or distinct structural responses, and whether individuals of the same species would exhibit distinct responses to water-use strategies between sites. We collected leaves from fully sun-exposed branches of individuals of the co-occurring species Tabebuia aurea and Tocoyena formosa , and performed light and scanning electron microscope observations of leaf anatomical traits to assess differences between sites. Leaf anatomical traits explained differences between sites only for Tabebuia aurea : individuals from the Cerrado exhibit thicker leaves and spongy and palisade parenchyma, and higher frequency of peltate trichomes, while those from the Caatinga show thicker abaxial and adaxial epidermis and a greater proportion of intercellular air space in the mesophyll. No differences are observed between individuals of T. formosa . Therefore, there is no convergent leaf anatomical response of species driven by environmental constraints. The variation in individuals of T. aurea between sites reflects contrasting functional adjustment aligning in opposite directions along the conservative-acquisitive strategy spectrum: Caatinga individuals show anatomical traits associated with an acquisitive strategy, while Cerrado individuals exhibit traits linked to a more conservative water-use strategy.

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