Ammonia Uptake Kinetics in Potamogeton peifoliatus under Nitrogen Replete and Deficient Conditions

Abstract

Potamogeton perfoliatus is an important SAV species in the low and middle portions of the Chesapeake Bay. In this study P. perfoliatus was observed to determine if apparent biphasic characteristics could be confirmed, and to determine if substrate nitrogen status was an influence on uptake patterns in the plant. Although the study could not confirm previously observed biphasic characteristics, an uptake velocity difference was observed between N-replete and N-deficient plants. Significant differences were observed in TKN data between N-replete (1.26% +/- 0.26) and N-deficient (0.78% -El- 0.15) at a 90% confidence level and 4 degrees of freedom. Ammonia uptake kinetics of N-replete and N-deficient plants were examined using draw down methods and were plotted using Michaelis-Menten model kinetics. In two trials, N-replete plants exhibited classic saturation hyperbolae using the Michaelis-Menten model with a Vmax of 4.47 and 8.47 and Km values of 2.10 and 28.95 respectively. N-deficient plants exhibited linear uptake kinetics. At high ammonia concentration (60uM), a 3 fold increase of ammonia uptake per gram fresh weight (12) versus N-replete plants (4) was observed. There were no observed significant differences of ammonia uptake at low ammonia concentrations (10uM) in N-replete (2-3) and N-deficient plants (1-1.5). The data indicates P. perfoliatus under N-deficient conditions maximizes uptake during pulses of high ammonia.