Ammonium nutrition enhances chlorophyll and glaucousness in Kohlrabi

Kohlrabi (Brassica oleracea var. gongylodes) plants were grown in the greenhouse under autumn conditions and fertilized either with pellets containing nitrogen as 40% ammonium sulphate and 60% urea or with nutrient solution containing nitrogen predominantly as nitrate. Plants given nitrogen as ammonium ions developed glaucous leaves compared to those supplied with nitrate which formed glossy leaves. Ammonium-induced glaucousness was the result of a two-fold increase in the amount of epicuticular wax and a markedly altered fine structure. Leaves from ammonium fertilized kohlrabi plants also showed a 21% increase in chlorophyll content together with a reduction in the chlorophyll a:b ratio and decreased ground state fluorescence compared to plants supplied with nitrate. Photosynthesis and stomatal transpiration were unaffected by the form of supplied nitrogen. (C) 1996 Annals of Botany Company