Nitrate metabolism in Scots pine seedlings during their first growing season

Fluctuations in nitrate reductase activity (NRA), nitrate, nitrite, protein and total nitrogen content of bare-root Scots pine seedlings (Pinus sylvestris L.) raised outdoors were investigated during the first growing season. Nitrate reductase activity was higher in roots than in needles, whereas NO(3) (-) content was higher in needles than in roots and increased in both from June to October. Nitrate reductase activity in roots correlated more closely with NO(3) (-) N in the soil than did NO(3) (-) in the roots. In autumn, there was a closer correlation between foliar NRA and NO(3) (-) in the needles than with NO(3) (-)-N in the soil. Nitrite was not detected in the seedlings during the growing season. Total nitrogen content decreased toward the autumn, whereas protein content initially decreased but increased again in autumn. Acrylic netting placed above the seedlings increased both air and soil temperatures and apparently accelerated the use of nitrate.