Analysis of bias in the calculation and measurement of plant mineral uptake rates

Abstract

Calculation of net ion uptake rate (F) from hydroponic solutions relies on balanced equations where F is equal to the initial minus the final ion content, plus fertilization. Knowledge is thus required of both volume (V), concentration (C) and of their temporal variations. The literature, however, proposes simplified equations that disregard variations in V and are thus strictly inaccurate. This paper studies the bias arising from such simplified formulae and also from deviations in V and C measurements. We used our experimental data and simulation to analyse the impact of different bias sources on F calculation, and to compare setups where C is regulated, or left to drift in order to study F = f(C). This paper reports two major findings, the first being that simplified equations distort F diurnal dynamics and ion uptake isotherms, yielding underestimated Michaelis-Menten parameters. The second shows the advantage of using C-regulated over unregulated systems to determine F when biased V and C measurements cannot be avoided. Regulated systems are able to minimize the biases on F, but the measurement of water uptake rate is compulsory. Therefore, simplified formulae should not be used.