A possible link between hydraulic properties and leaf habits in Hevea brasiliensis

A link exists between hydraulic traits and leaf habit. However, few attempts have addressed a possible link between hydraulic traits and altered leaf habit in introduced ranges. Within its native range, the Amazon rainforest, Hevea brasiliensis (Willd. ex A. Juss) Muell. Arg. is an evergreen but it becomes drought-deciduous in non-native ranges. The reason for this change remains poorly understood. The hydraulic-related traits, gas exchange rates and water status of H. brasiliensis and the co-occurring evergreen Drypetes indica (Muell. Arg.) Pax et Hoffm. were examined in Xishuangbanna, China. The water potential at turgor loss point in both species almost overlapped, but the water potential at which leaf relative water content reached 70% was more negative in D. indica. The water loss rate from excised leaves was quicker in H. brasiliensis. Leaf and stem hydraulic conductivity were more susceptible to drought-induced embolisms in H. brasiliensis than in D. indica. Vessels were significantly wider in H. brasiliensis but D. indica had more vessels. H. brasiliensis displayed higher rain-season gas exchange rates than D. indica. During the dry season, low soil water potential rendered water transport inefficient in H. brasiliensis; this effect was less pronounced in D. indica. D. indica has traits that help prevent hydraulic failure but has a low photosynthetic capacity. The opposite was found for H. brasiliensis. The results suggest that a combination of hydraulic traits, gas exchange characteristics and water status during the dry season might trigger a change in the leaf habits of H. brasiliensis in introduced ranges.