Effects of soil temperature on biomass and carbohydrate allocation in Scots pine (Pinus sylvestris) seedlings at the beginning of the growing season

Abstract

We studied effects of soil temperature on shoot and root extension growth and biomass and carbohydrate allocation in Scots pine (Pinus sylvestris L.) seedlings at the beginning of the growing season. One-year-old Scots pine seedlings were grown for 9 weeks at soil temperatures of 5, 9, 13 and 17 °C and an air temperature of 17 °C. Date of bud burst, and the elongation of shoots and roots were monitored. Biomass of current and previous season roots, stem and needles was determined at 3-week intervals. Starch, sucrose, glucose, fructose, sorbitol and inositol concentrations were determined in all plant parts except new roots. The timing of both bud burst and the onset of root elongation were unaffected by soil temperature. At Week 9, height growth was reduced and root extension growth was much less at a soil temperature of 5 °C than at higher soil temperatures. Total seedling biomass was lowest in the 5 °C soil temperature treatment and highest in the 13 °C treatment, but there was no statistically significant difference in total biomass between seedlings grown at 13 and 17 °C. In response to increasing soil temperature, belowground biomass increased markedly, resulting in a slightly higher allocation of biomass to belowground parts. Among treatments, root length was greatest at a soil temperature of 17 °C. The sugar content of old roots was unaffected by soil temperature, but the sugar content of new needles increased with increasing soil temperature. The starch content of all seedling parts was lowest in seedlings grown at 17 °C. Otherwise, soil temperature had no effect on seedling starch content.