Comparative growth and photosynthetic responses of native and adventive iceplant taxa to salinity stress

An ability to tolerate salinity can be critical for plants growing in coastal environments. We hypothesised that differences in salinity tolerance might explain variations in vigour and distribution patterns among four iceplant taxa on the Wellington coast. Growth rates, biomass allocation and quantum efficiencies of photosystem II were compared under three salinity levels for Carpobrotus edulis, Carpobrotus chilensis, Disphyma australe and a hybrid presumed to be C. edulis x D. australe. Carpobrotus edulis was significantly less tolerant of seawater-strength salinity relative to the other taxa. The data did not support a correlation between salinity tolerance and competitiveness in these iceplants. Chlorophyll a fluorescence measurements revealed no permanent adverse impacts on photosynthetic efficiency resulting from long-term exposure to salinity. However, salt-induced growth differences observed among iceplant taxa are probably due to the changes in their photosynthetic capacities.