title: Changes in gas exchange characteristics and water use efficiency of mangroves in response to salinity and vapour pressure deficit.
abstract: Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO2assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO2assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO2assimilation rate resulted in constant and similar intercellular CO2concentrations for leaves exposed to photon flux densities above 800 μmol·m-2·s-1in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO2assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO2concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.
authors.affiliation: Australian Institute of Marine Science, PMB No 3, 4810, Townsville MC, Queensland, Australia.
authors.forename: B F
authors.initials: BF
authors.lastname: Clough
authors.affiliation: Australian Institute of Marine Science, PMB No 3, 4810, Townsville MC, Queensland, Australia.
authors.forename: R G
authors.initials: RG
authors.lastname: Sim
keywords: Environmental gradients; Gas exchange; Mangrove; Water use efficiency