Wood trait trade-offs in desert plants: A triangular model to understand intra- and interspecific variations along an aridity gradient

Abstract

The hydraulic architecture of woody plants may show intra- and interspecific variations along aridity gradients as a result of wood trait trade-offs, which depend on species-specific abilities to withstand or evade drought. Plant hydraulic architecture can be defined as the set of different cell types involved in water transport through the soil–plant-atmosphere continuum. At the present time, there are two models designed to understand trade-offs among xylem wood functional traits, developed by Baas and Pratt, respectively. The first model presents a triangular trade-off space where three main plant xylem functions are linked to each other to provide resistance to embolism in evolutionary time. The second model depicts xylem cell types associated with their main functions, namely vessel-transport, parenchyma-storage and fibre-support. We propose here a new model considering the same relative xylem cell trait abundance for three desert species with different drought tolerance strategies along an aridity gradient of more than 300 mm. Hence, our model may account for both intra- and interspecific variations in wood traits for species from different localities along an aridity gradient. The tree Neltuma flexuosa showed little intraspecific variation in the medium drought resistance portion of the trade-off space, suggesting this species is independent from rainfall. Larrea divaricata showed a similar low intraspecific variation, but the spatial location in the trade-off space suggests it has a high tolerance to drought. The third species, Bulnesia retama, showed a higher intraspecific variation within the trade-off space, changing its hydraulic architecture in more fibre area with increasing aridity. Our model seems to be a generalized tool to assess both intra- and interspecific variations in trade-offs for hydraulic architecture among woody plants as a response to drought.