EFFECTS OF SOIL-WATER DEFICIT ON GAS-EXCHANGE CHARACTERISTICS AND WATER RELATIONS OF ORCHARD LYCHEE (LITCHI-CHINENSIS SONN) TREES

Eight-year-old lychee (Litchi chinensis Sonn.) trees, cv. 'Bengal,' gr owing in krasnozem soil were subjected to soil water deficit from one month before flowering until harvest by covering the ground with polye thylene sheeting and withholding irrigation. The ratio of daytime stom atal conductance of unirrigated to irrigated trees decreased 20% durin g the three months of increasing water deficit. Predawn leaf water pot entials of irrigated trees averaged about -0.3 MPa throughout the peri od, whereas they declined progressively to -0.9 MPa in unirrigated tre es. Minimum daytime leaf water potential in the unirrigated trees decr eased from -1.0 to -1.1 MPa at the beginning of the drought period to -2.2 to -2.4 MPa after three months, and calculated whole-plant conduc tance did not change with decreasing availability of water. The calcul ated soil-root water potential declined to less than -1.0 MPa in unirr igated trees. Capacitance effects on the relationship between leaf wat er potential and transpiration were significant only at low transpirat ion rates. Although unirrigated trees reduced soil water content at 0- 30 cm depths to an equivalent water potential of -1.0 MPa, fruit shedd ing was significantly less than in irrigated trees. Water deficit had no effect on the fresh weight of pericarp, but caused increased seed s ize and decreased fresh weight of flesh, resulting in fruit from unirr igated trees being 16% lower in total fresh weight per fruit than frui t from irrigated trees.