STOMATAL RESPONSE TO SHORT-TERM OSMOTIC-STRESS OF COWPEA PLANTS GIVEN VARYING PHOSPHORUS FERTILIZATION

Cowpea (Vigna unguiculata [L.] Walp. 'California Blackeye') plants were grown at seven rates of phosphorus (P) fertilization: 0.0 to 3.6 mM P provided weekly. When plants were eight weeks old, stomatal conductance (Cs) was measured before and after lowering soil water potential to -1.0 MPa with a sorbitol solution. Prestress Cs was between 4 and 5 mm/s in 0.0 to 2.4 P plants and varied between 5 and 7 mm/s in 3.0 and 3.6 P plants. Declines in Cs were similar after lowering of soil water potential in plants of all treatments except 0.6 P, which tended to have lower Cs.