A comparison of methods for estimating phosphorus uptake kinetics under steady‐state conditions¹

Contribution of Department of Soil Science, Oregon State University, Corvallis, OR 97331. Oregon Agric. Exp. Stn. Technical Paper no. 8906.

Abstract

Michaelis‐Menten kinetic parameters (I_max and K_M) are useful for describing nutrient uptake by plants. This paper compares two methods for estimating the kinetics of P uptake. Both methods employed a steady‐state hydroponic system to measure P uptake by wheat (Triticum aestivum L.) seedlings. In one method, uptake was measured from two P concentrations in nutrient solution, with I_max and K_M estimated by direct linear plot (DLP). In an alternate, multiple concentration (MC) method, uptake was measured from five P concentrations, and kinetic parameters were estimated by either nonlinear regression or the Hanes plot. The I_max and K_M, estimates obtained by the DLP method were compared to those obtained by the MC method. The MC method offered practical advantages. Unlike the DLP, it allowed estimation of the external P concentration at which net influx = 0 (C_min), and did not require a priori estimates of K_M and C_min. The MC method provided more precise median parameter estimates as indicated by smaller nonparametric confidence intervals. Using the median C_min value of 1.9 μM, the best estimates of I_max and K_M (and 96% confidence intervals) derived by nonlinear regression were 2.2 (1.6 to 2.8) nmol P g^‐1s^‐1, and 11 (10.6 to 12.9) μM, respectively.

Notes

Contribution of Department of Soil Science, Oregon State University, Corvallis, OR 97331. Oregon Agric. Exp. Stn. Technical Paper no. 8906.

Assistant Professor, College of Agriculture, Texas A&I University; Professor and Associate Professor, Department of Soil Science, Oregon State University.