Hydraulic architecture of Rhizophora mucronata under different salinity and flooding conditions.

Mangroves are tropical forests of the intertidal area. They have to endure a periodical inundation with salt water, on top of the tropical temperatures and often a succession of dry and rainy seasons as well. In consequence, the safety of the water transport in the mangrove habitat is constantly at risk because of the resulting strong negative pressure in the xylem vessels. The uniqueness of this ecosystem, concerning the environmental stresses mangroves are subjected to, raises the question how they manage to maintain a balanced water economy. An investigation of the different vessel characters can reveal the way mangroves are dealing with their peculiar habitat as well as with the prevailing climate and its plasticity.
In tropical trees the boundaries of annual growth rings are frequently absent or indistinct. Until recently, this implicated that a temporal analysis of the vessel characters in relationship with environmental variables was impossible. The discovery of annual growth rings in Rhizophora mucronata in Gazi Bay (Kenia) (Verheyden et al., 2004) unravelled this problem and opened the door to dendrochronological research in mangroves. The tree rings result from a seasonal, fluctuating vessel density. By combining a temporal analysis, with a spatial one, the potential of the vessel density as a proxy for temperature, relative humidity, salinity and inundation frequency was investigated (Schmitz, 2004). However, the general character of these findings needs to be investigated. We want to learn more about the (dis)similarities of the water transport system (i) in different mangrove species and (ii) at different geographical locations (associated with different habitat characteristics and climatic conditions). In this way we can contribute to the filling up of the gap in the dendro-ecological research about the environmental information archived in the mangrove wood.
In conclusion, the objective of this research project is twofold. On the one hand we aim at gaining insight in the hydraulic architecture of different mangrove species and under different environmental conditions. On the other, the potential of the analysed vessel characters will be tested as proxies for environmental factors.