The evolution of xylem vessels from tracheids is put forward as a key innovation that boosted hydraulic conductivity and photosynthetic capacities in angiosperms. Yet, the role of xylem anatomy and... Show moreThe evolution of xylem vessels from tracheids is put forward as a key innovation that boosted hydraulic conductivity and photosynthetic capacities in angiosperms. Yet, the role of xylem anatomy and interconduit pits in hydraulic performance across vesselless and vessel-bearing angiosperms is incompletely known, and there is a lack of functional comparisons of ultrastructural pits between species with different conduit types. We assessed xylem hydraulic conductivity and vulnerability to drought-induced embolism in 12 rain forest species from New Caledonia, including five vesselless species, and seven vessel-bearing species with scalariform perforation plates. We measured xylem conduit traits, along with ultrastructural features of the interconduit pits, to assess the relationships between conduit traits and hydraulic efficiency and safety. In spite of major differences in conduit diameter, conduit density, and the presence/absence of perforation plates, the species studied showed similar hydraulic conductivity and vulnerability to drought-induced embolism, indicating functional similarity between both types of conduits. Interconduit pit membrane thickness (Tm) was the only measured anatomical feature that showed a relationship to significant vulnerability to embolism. Our results suggest that the incidence of drought in rain forest ecosystems can have similar effects on species bearing water-conducting cells with different morphologies. Show less
Increases in drought-induced tree mortality are being observedin tropical rain forests worldwide and are also likely to affectthe geographical distribution of tropical vegetation. However,the... Show moreIncreases in drought-induced tree mortality are being observedin tropical rain forests worldwide and are also likely to affectthe geographical distribution of tropical vegetation. However,the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P50) of 13woody species endemic to New Caledonia and with differentxylem conduit morphologies. We examined the relation be-tween P50, along with other leaf and xylem functional traits,and a range of habitat variables. Selected species had P50values ranging between 4.03 and 2.00 MPa with most species falling in a narrow range of resistance to embolism above 2.7 MPa. Embolism vulnerability was significantly correlatedwith elevation, mean annual temperature and percentage ofspecies occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P50. Commonly used functional traits such as wood density and leaf traits were notrelated to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as amajor driver of species environmental distribution. Drought-induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rainforest woody species. Show less
