How drought and deciduousness shape xylem plasticity in three Costa Rican woody plant species

This paper explores the phenotypic plasticity of xylem in tropical trees in order to test the hypothesis that different leaf phenological patterns influence levels of xylem plasticity. Wood anatomy was studied in the wet-deciduous species Cordia alliodora (Ruiz & Pav.) Oken, the dry-deciduous species Tabebuia rosea (Bertol.) DC., and the evergreen species Ocotea veraguensis (Meisn.) Mez., collected from seasonally dry forest and tropical cloud forest in Costa Rica. Xylem plasticity and trait conservatism were examined by analysing the coefficient of variation (CV) and the relative distance plasticity index (RDPI) of xylem anatomical traits. The two deciduous species exhibited wider vessels, lower wood density, and higher Huber values than the evergreen species. Furthermore, intervessel connectivity was highest for the two deciduous species in seasonally dry forest compared to cloud forest, whereas the opposite was found for the evergreen species. Overall highest trait variability was found for all plants at the seasonally dry site. The evergreen species O. veraguensis had the highest plasticity values compared to the deciduous species. Highest plasticity was found for vessel composition index (vessel area/vessel number), while strongest trait conservatism was found for vessel diameter. In conclusion, our data indicate that evergreen O. veraguensis does not show less xylem plasticity than the two deciduous tree species studied.