Seedling growth responses of Banksia littoralis and Melaleuca preissiana to soil salinity

Banksia littoralis (Swamp Banksia) and Melaleuca preissiana (Moonah) are two tree species that are commonly associated with wetland fringes and inter-dunal depressions of the Swan Coastal Plain. These low-lying areas are prone to hydrological disturbances and salinisation. The growth and tolerance of B. littoralis and M. preissiana seedlings to increased soil salinity was examined via a pottrial that lasted for 70 days with weekly watering of 0, 50, 100 and 150 mM of NaCl solution. Nomortality was observed for either species within any of the salt treatments. M. preissiana seedlingsshowed no difference in their growth response or above-ground biomass allocation. B. littoralisseedlings showed a substantial reduction in relative growth rate and net assimilation rate for solutions greater than 100 mM NaCl. This resulted from an overall reduction in shoot dry mass,with less leaf area being produced per unit leaf mass, and caused recently produced leaves tobecome dehydrated. These results suggest that M. preissiana seedlings are capable tolerating soilswith an electrical conductivity of at least 1650 μS cm-1, whereas seedling growth of B. littoralis issignificantly reduced for soil conductivity > 980 μS cm-1. From this study it can be concluded thatsoil salinisation will have a more detrimental impact on B. littoralis seedling recruitment than co-occurring M. preissiana seedlings.