Abstract: | Ricinus communis L. var. Gibsonii was grown in Long Ashton nutrientmedium with either 12mol m3 NO3 or 8.0 mol m3NH+4 as N source. Two plants from each N treatment were harvestedtwice a week and analysed for C, N, P, S, NO3, SO24ClK+Na+, Ca2+ Mg2+ and ash alkalinity. Statistical analysis of thedata showed that the effect of age and N source was differentfor the chemical variables analysed. Thus Na+] was unaffectedby age or N source, and for both N sources Mg2+] started atthe same level and decreased at the same rate as the plantsmatured. With NH+4 as N source, SO24] was higher thanwith NO3, but did not alter with age. The concentrations,in mmol g1 dry wt, of C, organic N, K+ and Ca2+ weredifferent for the two N sources, but the levels of these variablesaltered with age in the same way for both N sources; i.e. therewas no age x N interaction. In the case of P, NO3, Cl and COO, however,age-related variations were different for the two N sources.It is concluded, inter alia, that Na+] is determined by externalNa+] alone, and that K+, Ca2+ and Cl are the inorganicions actively involved in charge balance during ion uptake bythe roots. Key words: Ontogeny, Chemical composition, Plant nutrition |