ARE THE EFFECTS OF SALINITY ON GROWTH AND LEAF GAS-EXCHANGE RELATED

The responses of growth and leaf gas exchange to increasing salinity w ere measured in two halophytes [Atriplex nummularia (C-4), Atriplex ha stata (C-3)] and one glycophyte [Hordeum vulgare (C-3)]. The growth (d ry mass) of both the halophytes was significantly increased, by 54 and 17 %, respectively, as salinity was increased in the range 0-200 mol m(-3) NaCl. However, net CO2 assimilation rate (P-N), the intercellula r CO2 concentration (c(i)) and leaf conductance (g(l)) were unaffected . At higher levels of salinity (in the range 400 - 600 mol m(-3) NaCl) the growth of the two halophytes was severely reduced (by 44 and 51 % , respectively). At these levels of salinity P-N, g(l) and c(i) were s ignificantly depressed. 25 mol m(-3) NaCl significantly reduced the gr owth of H. vulgare by 44 %, but had no effect on P-N, g(l) and c(i). H owever, at 100 mol m(-3) NaCl, where growth was decreased by 62 %, P-N and g(i) were significantly reduced while ci was unaltered. There was thus, no association between the effects of salinity on growth and le af gas exchange at low salinities (25-200 mol m(-3) NaCl). At higher s alinities, leaf gas exchange and growth were both severely inhibited b ut it is unlikely that a direct causal relationship existed. At these salinities sodium concentration in the leaves (tissue water basis) was above 400 mol m(-3) in the halophytes and above 100 mol m(-3) in H. v ulgare which possibly affected both growth and leaf gas exchange indep endently. Also, the effects of salinity on total leaf chlorophyll conc entration and net CO2 assimilation rate expressed on a chlorophyll (ch l) basis (P-chl) were no better related to growth than was P-N.