Nutrient Influences on Leaf Photosynthesis: EFFECTS OF NITROGEN, PHOSPHORUS, AND POTASSIUM FOR GOSSYPIUM HIRSUTUM L.

The net rate of CO(2) uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO(3) (-), PO(4) (2-), or K(+). The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO(2) uptake rate at low nutrient levels was due to a decrease in the CO(2) conductance expressed per unit mesophyll cell wall area (g(cell) (CO(2) )). The use of g(cell) (CO(2) ) and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO(2) uptake of leaves.