GROWTH AND GAS-EXCHANGE PARAMETERS OF CITRUS PLANTS STRESSED WITH DIFFERENT SALTS

Valencia orange scions ( Citrus sinensis (L.) Osbeck) budded to either Cleopatra mandarin (Citrus reticulata) or Poncirus trifoliata ([L.] R af.) rootstocks were treated with 60 mmol/L of different salts (NaCl, KCl and NaNO3) in order to distinguish the specific effects of each io n on growth and gas exchange parameters. The chloride salts markedly r educed plant growth in both scion-root stock combinations whereas NaNO 3 had very little effect. Poncirus trifoliata accumulated relatively m ore Cl- in leaves and less in roots than Cleopatra mandarin. In contra st, the sodium concentration in leaves was higher in Cleopatra mandari n than in Poncirus trifoliata. The chloride and sodium contents in lea ves of both scion-rootstock combinations were depressed when 30 mmol/L Ca(NO3)(2) was added to the culture solution. Both chloride salts (KC l and NaCl) caused a similar reduction in photosynthesis and stomatal conductance, whereas NaNO3 had no detectable effects on these paramete rs. Addition of calcium nitrate considerably increased growth and the gas exchange parameters in plants exposed to chloride salts and also r educed ion uptake and transport. Taken together, these results indicat e that the salinity effects on growth and gas exchange parameters appa rently are induced by the external chloride supply.