title: THE RELATIVE IMPORTANCE OF WATER MOTION ON NITROGEN UPTAKE BY THE SUBTIDAL MACROALGA ADAMSIELLA CHAUVINII (RHODOPHYTA) IN WINTER AND SUMMER(1).
abstract: The influence of seawater velocity (1.5-12 cm · s(-1) ) on inorganic nitrogen (N) uptake by the soft-sediment perennial macroalga Adamsiella chauvinii (Harv.) L. E. Phillips et W. A. Nelson (Rhodophyta) was determined seasonally by measuring uptake rate in a laboratory flume. Regardless of N tissue content, water velocity had no influence on NO3 (-) uptake in either winter or summer, indicating that NO3 (-) -uptake rate was biologically limited. However, when thalli were N limited, increasing water velocity increased NH4 (+) uptake, suggesting that mass-transfer limitation of NH4 (+) is likely during summer for natural populations. Uptake kinetics (Vmax , Ks ) were similar among three populations of A. chauvinii at sites with different mean flow speeds; however, uptake rates of NO3 (-) and NH4 (+) were lower in summer (when N status was generally low) than in winter. Our results highlight how N uptake can be affected by seasonal changes in the physiology of a macroalga and that further investigation of N uptake of different macroalgae (red, brown, and green) during different seasons is important in determining the relative influence of water velocity on nutrient uptake.
authors.affiliation: Department of Botany, University of Otago, PO Box 56, Dunedin, New ZealandDepartment of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New ZealandNational Institute for Water and Atmospheric Research, PO Box 14, Wellington, New Zealand.
authors.forename: Louise T
authors.initials: LT
authors.lastname: Kregting
authors.affiliation: Department of Botany, University of Otago, PO Box 56, Dunedin, New ZealandDepartment of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New ZealandNational Institute for Water and Atmospheric Research, PO Box 14, Wellington, New Zealand.
authors.forename: Catriona L
authors.initials: CL
authors.lastname: Hurd
authors.affiliation: Department of Botany, University of Otago, PO Box 56, Dunedin, New ZealandDepartment of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New ZealandNational Institute for Water and Atmospheric Research, PO Box 14, Wellington, New Zealand.
authors.forename: Conrad A
authors.initials: CA
authors.lastname: Pilditch
authors.affiliation: Department of Botany, University of Otago, PO Box 56, Dunedin, New ZealandDepartment of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New ZealandNational Institute for Water and Atmospheric Research, PO Box 14, Wellington, New Zealand.
authors.forename: Craig L
authors.initials: CL
authors.lastname: Stevens
keywords: Adamsiella chauvinii; ammonium; nitrate; nitrogen uptake; subtidal macroalgae; water velocity