RESPONSES OF SQUASH TO SALINITY, WATERLOGGING, AND SUBSEQUENT DRAINAGE .1. GAS-EXCHANGE, WATER RELATIONS, AND NITROGEN STATUS

To examine plant physiological responses to salinity, waterlogging, and subsequent drainage, summer squash (Cucurbita pepo) was grown in well watered or flooded sand with full-strength Hoagland solution containing 100 mol/m(3) sodium chloride (NaCl) or no NaCl for 14 d. Half of the waterlogged plants were transferred to drained conditions for 7 d of recovery, while half of salinized plants were continuously salinized until 21 d. Waterlogging or salinity alone reduced photosynthetic rate (Pn), stomatal conductance (gs), and leaf chlorophyll content to a greater extent with waterlogging. Waterlogging alone, however, did not affect leaf water potential (psi leaf) Salinity alone did not affect leaf and root nitrogen content. A combination of waterlogging and salinity exacerbated the adverse effects of each factor alone for Pn, gs, leaf chlorophyll, and nitrogen content, but not for psi leaf. Seven days after termination of waterlogging, a full recovery occurred for gs, psi leaf, leaf chlorophyll content, and leaf and root nitrogen content for waterlogged plants under non-saline conditions, while for waterlogged plants under saline conditions those parameters did not achieve that of the control value.