Phosphorus and Potassium Uptake Kinetics in Red Maple Seedlings

Abstract

Abstract Acquisition of nutrients by tree roots generally is viewed as a complex process. Models that make use of Michaelis-Menten kinetics concepts provide a means to mechanistically simulate nutrient uptake. The objectives of this study were to provide: (1) estimates of the Michaelis-Menten parameters Imax, Km, and Cmin for P and K uptake by red maple (Acer rubrum L.) seedlings, and (2) to test the efficacy of these values in the modeling context by using the Barber-Cushman nutrient uptake model as a test vehicle. A nutrient depletion approach that used intact seedlings and transient conditions was used to define the kinetics values. These estimates were combined with literature values to provide a full parameter set for the model. Uptake of P proceeded rapidly and yielded an average Imax of 5.5E-6 μmol cm-2 s-1. Mean Km and Cmin values for P were 15.0 and 0.001 μmol mL-1, respectively. Potassium uptake was slower with a mean Imax of 3.8E-6 μmol cm-2 s-1, and the Km and Cmin values were 10.5 and 0.003 μmol mL-1, respectively. Simulated P uptake compared poorly with observed uptake (0.8 vs. 830 μmols). However, additional model runs indicated that the lack of agreement was more the result of a low estimate of soil solution P concentration than a problem with the P kinetics values. Simulated K uptake was in much better agreement with the observed value (891 vs. 1890 μmols). The Cmin values for P and K reflect an ability to continue root uptake at extremely low solution concentrations. This may contribute to the “supergeneralist” status accorded red maple. This study indicates these Imax, Km, and Cmin values can be used in the Barber-Cushman model to simulate P and K uptake by red maple. However, use of these Imax, Km, and Cmin values needs to be tempered with the understanding that several interacting factors influence uptake. This caveat is important when generic literature values provide some or all of the numbers used to initialize the model. FOR. SCI. 47(3):397–402.