HOW DIFFERENCES IN THE FIELD INFLUENCE CU, FE AND ZN UPTAKE BY HALIMIONE-PORTULACOIDES AND SPARTINA-MARITIMA

The highest metal levels of Cu, Fe and Zn were always found in Spartina maritima roots; for Halimione portulacoides the highest Cu and Fe levels were also observed in the roots although mean Cu and Zn values in the roots and leaves were not significantly different at the 0.05 significance level. Lower metal and biomass values were found in Spartina collected in soils where continuous waterlogging occurs, which also limits the height of this plant. Nevertheless, these soils contained high metal levels. Iron accumulates in standing dead leaves and culms of Spartina while for Cu and Zn no significant differences were observed between dead and living organs. Generally the top layer of the soils (0-5 cm depth), contains higher Cu and Zn levels. For Halimione bearing soils Fe slightly increases with depth while for Spartina no variation with depth was observed (P < 0.05); mean Fe values at the different stations were not significantly different (P < 0.05). For both species, the interactions between sampling site and substratum were not significant for Fe (P < 0.05), although for Halimione factors can act independently which is not the case for Spartina. The percentages of the total Cu, Fe and Zn in the soils bearing Halimione, extracted by bidistilled water (minimum available for root uptake), were approximately constant and independent of the concentration and nature of the matrix. The availability of Cu is very weak contrasting with that of Zn, Fe presents an intermediate behaviour. However, roots of H. portulacoides and S. maritima contained, Cu levels higher than the bidistilled water extractable soil levels, as seen by the ratio soil level/root level, indicating that roots constitute an important vector for Cu recycling and mobilization.