Responses of Scots pine (Pinus sylvestris) seedlings grown in different nutrient regimes to changing root zone temperature in spring

We examined effects of nutrient availability and changing root zone tempera ture (RZT) on growth, gas exchange and plasma membrane H+-ATPase (PM-ATPase ) activity of roots of 1-year-old Scots pine (Pinus sylvestris L.) seedling s during spring flushing. The 6-week growth-chamber experiment was carried out in hydroponic cultures that supplied the seedlings with low (0.5 mM N) or high (3 mM N) nutrient concentration and two rates of increase in RZT we re simulated: slow warming (SW-treatment) and fast warming (FW-treatment). Air temperature, humidity, and light conditions were similar in all treatme nts. Growth of roots and shoots was retarded at low RZT, and fresh mass inc rement of roots was closely correlated with RZT sum. High nutrient availabi lity increased nitrogen concentrations of needles and stems, but only at RZ Ts >13 degrees C, Low RZT and low availability of nutrients suppressed as e xchange of the seedlings. Real PM-ATPase activity was highly dependent on R ZT. At high RZTs, real PM-ATPase activity was affected by nutrient availabi lity but this effect was related to root growth. We conclude that, under co nditions of high nutrient availability, Scots pine seedlings can compensate for the suppressive effects of long-term exposure to low RZT by rapidly ac celerating growth, gas exchange and root metabolism, but only when RZT has increased above a threshold value, which was 13 degrees C in this study.