4. Discussion
4.1. Effect of N and salt on metal uptake and tolerance by R. stylosa
Present results from R. stylosa showed that the phytotoxicity
of metals can be strongly modulated in response to its growth
conditions. Aggravated metallic toxicities were observed under N
deficient conditions, a moderate salt application, oppositely, alleviated
metal-induced inhibition. Artificial mangrove ecosystem has
been considered as a low-cost and high-efficiency wetland system
for the treatment of municipal wastewater (Tam and Wong, 1997).
However, excessive contaminants such as heavy metals accumulated
in sediments may inhibit normal growth of mangrove plants
(MacFarlane et al., 2007), thus the improvement of metal tolerance
by plants is important. The present study provides useful evidence
on how to alleviate metal-induced inhibition (e.g., a suitable