© 2002 Heron Publishing—Victoria, Canada
Seasonal variation in nitrogen net uptake and root plasma membrane H+-ATPase activity of Scots pine seedlings as affected by nutrient availability
Sari Iivonen (1) and Elina Vapaavuori (1, 2)
1. Finnish Forest Research Institute, Suonenjoki Research Station, Juntintie 40, FIN-77600 Suonenjoki, Finland / 2. Author to whom correspondence should be addressed (Elina.Vapaavuori@metla.fi) / Received November 9, 2000; accepted April 21, 2001; published online December 1, 2001
Summary
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.
Keywords:
hydroponic culture, Pinus sylvestris, potential activity, real activity, root zone temperature, shoot.
