Water relations and xylem transport of nutrients in pepper plants grown under two different salts stress regimes

Two iso-osmotic concentrations of NaCl and Na^sub 2^SO^sub 4^ were used for discriminating between the effects of specific ion toxicities of salt stress on pepper plants (Capsicum annuum L.) grown in hydroponic conditions, in a controlled-environment greenhouse. The two salts were applied to plants at different electrical conductivities, and leaf water relations, osmotic adjustment and root hydraulic conductance were measured. Leaf water potential (Ψ^sub w^), leaf osmotic potential (Ψ^sub o^) and leaf turgor potential (Ψ^sub p^) decreased significantly when EC increased, but the decrease was less for NaCl- than for Na^sub 2^SO^sub 4^-treated plants. The reduction in stomatal conductance was higher for NaCl-treated plants. There were no differences in the effect of both treatments on the osmotic adjustment, and a reduction in root hydraulic conductance and the flux of solutes into the xylem was observed, except for the saline ions (Na^sup +^, Cl^sup -^ and SO^sub 4^^sup 2-^). Therefore, pepper growth decreased with increasing salinity because the plants were unable to adjust osmotically or because of the toxic effects of Cl^sup -^, SO^sub 4^^sup 2-^ and/or Na^sup +^. However, turgor of NaCl-treated plants was maintained at low EC (3 and 4 dS m^sup -1^) probably due to the maintenance of water transport into the plant (decrease of stomatal conductance), which, together with the lower concentration of Na^sup +^ in the plant tissues compared with the Na^sub 2^SO^sub 4^ treatment, could be the cause of the smaller decrease in growth.[PUBLICATION ABSTRACT]