Growth, carbohydrate and nutrient allocation of Scots pine seedlings after exposure to simulated low soil temperature in spring

The effects of sustained low soil temperature on growth and allocation of biomass and carbohydrates in Scots pine ( Pinus sylvestris L.) were studied by exposing 1-year-old seedlings to soil temperatures of 5degreesC for 0, 3, 6 or 9 weeks and subsequently for 9 weeks at 13degreesC. Growth at 5degreesC soil temperature at the beginning of the growing season reduced the height of new shoots but the length of the cold soil period did not affect the final height. Some new root tips emerged during the 5degreesC soil temperature period. Prolific root growth did not start until the soil temperature was increased from 5 to 13degreesC, but new root growth was scarce during the first 3 weeks even at 13degreesC, a clearly more favourable soil temperature than 5degreesC. Seedlings exposed to a temperature exceeding 5degreesC over any 3-week period during the first 9 weeks had above- and below-ground biomasses that were equivalent, whereas continual exposure to 5degreesC reduced shoot and root growth. The above- ground biomass of the seedlings did not increase any more after Week 12, nor did the below-ground biomass after Week 15. Biomass allocation among the different parts of the seedlings was not greatly affected by the length of the cold soil period. Our results indicate that the accumulation of above- ground biomass is mainly dependent on the air temperature and not soil temperature. Element allocation followed the pattern of biomass allocation, except for N, which increased in the above- ground parts throughout the experiment, and Fe, which had already accumulated during the first 3 weeks. The seedlings grown for a longer time at low soil temperatures contained lower amounts of starch but similar amounts of soluble sugars throughout the experiment.