THE INFLUENCE OF CYST NEMATODES AND DROUGHT ON POTATO GROWTH .3. EFFECTS ON CARBON ISOTOPE FRACTIONATION

A good agreement was found between drought induced water-use efficiencies and carbon isotope fractionation of potato plants of the same age. Discrimination of Carbon-13 isotope increased with plant age and with the rank order of the distinguished plant organs. In young plants, nematode infection (contrary to drought) reduced C-13 discrimination but also reduced the water-use efficiency, leading to the conclusion that nematode infection, by slowing down the plant metabolism may have reduced the extrusion of C-13. Towards senescence both nematode infection and drought reduced C-13 discrimination and increased water-use efficiencies indicating that then nematode caused water stress in the plants.