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Phosphorus and Potassium Uptake Kinetics in Red Maple Seedlings

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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 I max, K m , and C min 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 I max of 5.5E-6 μmol cm-2 s-1. Mean K m and C min values for P were 15.0 and 0.001 μmol mL-1, respectively. Potassium uptake was slower with a mean I max of 3.8E-6 μmol cm-2 s-1, and the K m and C min 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 C min 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 I max, K m, and C min values can be used in the Barber-Cushman model to simulate P and K uptake by red maple. However, use of these I max, K m, and C min 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.

Keywords: Barber-Cushman model; Cmin; Imax; Km; Nutrient influx; environmental management; forest; forest management; forest resources; forestry; forestry research; forestry science; natural resource management; natural resources; root surface area

Document Type: Miscellaneous

Affiliations: 1: Professor and Research Assistant Department of Forestry, Iowa State University, 253 Bessey Hall, Ames, IA, 50011-1021, Phone: (515) 294-1166; Fax: (515) 294-2995 jmkelly@iastate.edu 2: Professor and Research Assistant Department of Forestry, Iowa State University, 253 Bessey Hall, Ames, IA, 50011-1021, Phone: (515) 294-1166; Fax: (515) 294-2995

Publication date: August 1, 2001

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