Relative Uptake Rates of Inorganic Nutrients by NO3-and NH4+GrownRicinus communisand by twoPlantago Species

Allen, S., Thomas, G. E. and Raven, J. A. 1986. Relative uptake rates of inorganic nutrients by $NO3-$ and $NH4+$ grown Ricinus communis and by two Plantago species.—J. exp. Bot. 37: 419–428. The relative rates of uptake and assimilation of C, N, P, S, Cl⁻, K⁺ , Na⁺ Ca²⁺ and Mg²⁺ by $NO3-$ and $NH4+$ grown Ricinus conimunis and by NH₄NO₃- grown Plantago lanceolata and P. major were calculated from data presented elsewhere. Results showed that for $NO3-$ grown Ricinus the short term relative uptake rates, $X¯Δt$ for each nutrient X did not change significantly over the steady-state period of exponential growth. The average $X¯Δt$ gave $X¯$, the mean relative uptake rate during exponential growth, for each nutrient. The amount of each nutrient taken up from a nutrient solution over a period of time could, therefore, be calculated. For $NO3-$ and $NH4+$-grown R. communis, the relative uptake rate of each nutrient was a constant fraction of the relative rate of carbon assimilation. It is suggested that this is typical of plants of cauline habit. For both Plantago spp., the relative rates of nitrogen uptake and assimilation fell significantly during the exponential growth phase It is suggested that this could be a characteristic of the growth habit of the rosette plant.