title: Seasonal variation in nitrogen net uptake and root plasma membrane H+-ATPase activity of Scots pine seedlings as affected by nutrient availability.
abstract: We examined changes in nitrogen (N) net uptake and activity and amount of plasma membrane H+-ATPase (PM-ATPase) in roots of hydroponically cultured Scots pine (Pinus sylvestris L.) seedlings throughout a simulated second growing season. Seedlings were grown with low (0.25 mM N) or high (2.5 mM N) nutrient availability to determine whether root PM-ATPase is dependent on an external nutrient supply. Climatic conditions in the growth chamber simulated the mean growing season from May to mid-October in southern Finland. Root PM-ATPase activity varied considerably during the growing season and was higher in current-year roots than in previous-year roots. Total PM-ATPase activity of current-year roots was highest at the end of the growing season, whereas PM-ATPase activity per unit fresh mass of current-year roots and specific absorption rate of N were highest in mid-July and decreased at the end of the growing season. This indicates that the decrease in PM-ATPase activity per unit fresh mass of the roots at the end of the growing season was compensated by the increased size of the root system. Seasonal variation in PM-ATPase activity had no clear dependence on root zone temperature. The response of PM-ATPase to root zone temperature was dependent on the developmental stage of the seedling. High nutrient availability resulted in increased root PM-ATPase activity and an extended period of root growth in autumn.
authors.affiliation: Finnish Forest Research Institute, Suonenjoki Research Station, Juntintie 40, FIN-77600 Suonenjoki, Finland.
authors.forename: Sari
authors.initials: S
authors.lastname: Iivonen
authors.forename: Elina
authors.initials: E
authors.lastname: Vapaavuori
mesh_terms: D002462:Cell Membrane / Q000201:enzymology / Q000502:physiology; D005387:Finland; D009584:Nitrogen / Q000378:metabolism; D028223:Pinus / Q000201:enzymology / Q000502:physiology*; D018517:Plant Roots / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D018520:Plant Shoots / Q000201:enzymology / Q000502:physiology; D006180:Proton-Translocating ATPases / Q000378:metabolism / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000201:enzymology / Q000502:physiology*
chemical_list: D006180:Proton-Translocating ATPases; D009584:Nitrogen