GROWTH AND ION ACCUMULATION OF 2 RAPID-CYCLING BRASSICA SPECIES DIFFERING IN SALT TOLERANCE

The response of two rapid-cycling Brassica species differing in tolera nce to seawater salinity was studied over a period of 24 days. In resp onse to 8 dS m-1 salinity, the two Brassica species showed clear diffe rences in the changes in relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR). The RGR of B. napus was slightly reduced by salinity, whereas the RGR of B. carinata was largely reduc ed in the early stages of salinization. LAR of B. napus was affected b y salinity in the later stages of growth and significantly correlated with the reduction in RGR. On the other hand, the NAR of B. carinata w as decreased by salinity, corresponding to the decrease of the RGR of B. carinata. The NAR of B. napus was not significantly affected by sal inity according to analysis of covariance. The shoot concentrations of Na, Mg and Cl increased while the concentrations of K and Ca decrease d sharply during the first 5 days of salinization; subsequently, all i on concentrations remained relatively constant. The concentrations of Na, K, Ca, Mg and Cl in the root were similarly affected by salinity. There were no significant differences of ion concentrations between sp ecies that could be related to the differences in salt tolerance. Thus , the differences in salt tolerance between species can not be related to differences in specific-ion effects, but may be related to some fa ctor that reduces the NAR of B. carinata during the early stages of gr owth.