Kinetics of ammonium, nitrate and phosphorus uptake by Canna indica and Schoenoplectus validus

Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Love and D. Love is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (I-max) and Michaelis-Menten constant (K-m) were estimated by iterative curve fitting. The I-max for NH4-N (623 mu mol g(-1) dry root weight h(-1)) was significantly higher than that for NO3-N (338 mu mol g(-1) dry root weight h(-1)) in S. validus. In contrast, no difference was observed in C. indica. The I-max values for NO3-N and NH4-N were higher in S. validus than in C indica. A significantly lower K-m was detected for NO3-N uptake in C. indica (385 mu mol L-1) compared to that in S. validus (1908 mu mol L-1). The I-max for PO4-P did not differ between the plant species. The K-m for PO4-P was significantly higher in C indica (157 mu mol L-1) than in S. validus (60 mu mol L-1). In conclusion, we found that S. validus preferred NH4-N over NO3-N, had greater capacity for N uptake and higher affinity for PO4-P, but C. indica had greater affinity for NO3-N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes. (C) 2009 Elsevier B.V. All rights reserved.