A Method for Characterizing the Relation between Nutrient Concentration and Flux into Roots of Intact Plants

Abstract

A method based on the rate of depletion of a nutrient from solution was developed to characterize nutrient flux of plant roots. Nutrient concentration of the solution was measured at a series of time intervals to describe the complete depletion curve. An integrated rate equation, based on a Michaelis-Menten model, was developed and fit to the data of the depletion curve using a least-square procedure. The A procedure was also developed to measure uptake rate at constant concentration by adding nutrients to the pot at a constant rate that matched net influx into the root. This method also provides a means of measuring diurnal fluctuations in net influx rates.Knowledge of the relation between the rate of ion absorption by plant roots and the concentration of the ion external to the root is important for doing plant nutrition studies, for investigating ion absorption mechanisms, and for evaluating mechanisms supplying nutrients to roots growing in soil (6, 10). Hence, a convenient procedure that mathematically describes the kinetics of ion absorption would be useful.Ion absorption rate as related to ion concentration in the external solution has usually been measured using short term absorption by excised roots of isotopically labeled ions from solution (4) and long term absorption by intact plants from solutions maintained approximately at constant concentration (1). In the first, only ions with a convenient isotope for labeling can be studied and in both, separate measurements of uptake rate must be made for each of a graded series of ion con- THEORYWhen roots are in a solution containing salts, ions may move both into and out of the root. The terms we use to describe this ion movement are: influx, movement of ions from the external solution into the root; I, the rate of influx per unit length of root; efflux, the movement of ions out of the root into the external solution; E, the rate of efflux per unit length of root, and In, the net rate of influx per unit root length which is equal to I -E. The values of I, E, and ln in this paper are in terms of root length; however, root surface area, or root weight could be used if desired.When plants are grown in a solution of a constant volume, v, the decrease in ion content of the solution measures the net amount of the respective ion absorbed. The amount of ion in the nutrient solution, Q, is given by equation 1 where c is the ion concentration in solution. Q = cv (1) A plot of Q versus time, t, gives a curve showing the depletion of the ion from solution resulting from plant absorption and is called the depletion curve. The net influx per pot at any point on this curve is given by -dQ/dt. The slope of the curve can be estimated by expressing Q as a function of t and calculating the derivative. A relation Q = f(t) can be obtained by fitting the data using a parabolic spline function (3) or a cubic spline function (13). Both functions consist of a number of segments called splines fixed by the experimenter which describe the relation by a series of parabolic ...

Root Morphology and Nutrient Uptake Kinetics by Australian Cedar Clones

“…Determination of the kinetic parameters V max , K m and, C m was based on the principle proposed by Claassen and Barber (1974), which involves quantifying the reduction in nutrient concentration in the solution resulting from the uptake by the plants. For this, aliquots of 10 mL were removed from the depletion solution, the first being collected at "time zero," before adding the seedlings, and the others at intervals of one hour over a period of 12 hours.…”

Kinetics of nitrate and ammonium absorption and accompanying H+fluxes in roots ofLolium perenneL. and N2‐fixingTrifolium repensL.

“…Short-term results obtained by the use of '•'N and '^N are usually in agreetnent (Clarkson et al, 1996), Kinetic paratneters have also been derived on the basis of tneasuretnents of the rate of depletion of NO3" or NH4^ tVotn the nutrient solution surrounding the roots (e.g. Claassen & Barber 1974; Van de Dijk et al 1982;Goyal & Huffaker 1986), Since the latter tnethod is not able to distinguish between added or effluxed NO," and NH4' *^, it provides data for net uptake, not influx, of NO3" and NH/, Information on differences in competitive nutrient uptake relations in mixtures of legumes and grass species is limited. Rao et al (1993) reported that some non-nodulated legumes (Cicer arietinitn L., Cajatius cajan and Aractiis hypogaea L.) had a higher affinity (lower K,J and a higher maximum net influx (V^ax) for NH4"^ than did cereals (Sorgttuni hieotor, Pennisetum glaucim and Zea mays L.).…”

Parâmetros cinéticos e morfológicos da absorção de nutrientes em cultivares de milho com variabilidade genética contrastante

“…Os parâmetros cinéticos foram determinados pelo princípio descrito por Claassen & Barber (1974), o qual consiste em quantificar a diminuição da concentração da solução de acordo com a absorção. Esses parâmetros foram avaliados 14 dias após o transplante das plantas para N, P e K, e 20 dias após o transplante para Ca e Mg, em plantas com 20 e 26 dias respectivamente.…”

“…Os valores dos parâmetros cinéticos (I max , K m e C min ) foram calculados por meio do programa 'software' Cinética (Ruiz, 1985), que se baseia no princípio desenvolvido por Claassen & Barber (1974). Esse programa calcula o I max por meio de uma equação linear, e o K m por equações do tipo exponencial, potencial ou exponencial-recíproco.…”