Effects of soil temperature on shoot and root growth and nutrient uptake of 5-year-old Norway spruce seedlings

Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 degreesC during the first (GSI) and third growing seasons (GSIII), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 degreesC during the second growing season (GSII). In GSII, shoot diameter growth was lowest in the 21 degreesC treatment and root growth was lowest in the 9 degreesC treatment. In GSIII, shoot height and root length growth improved in seedlings that had been kept at 9 degreesC during GSII, indicating compensatory growth in response to increased soil temperature. The temporary decrease in soil temperature had no long-lasting significant effect on seedling biomass or total nutrient uptake. At the end of GSIII, fine roots of seedlings exposed to a soil temperature of 21 degreesC in GSII were distributed more evenly between the organic and mineral soil layers than roots of seedlings in the other treatments. During GSII and GSIII, root growth started earlier than shoot growth, decreased during the rapid shoot elongation phase and increased again as shoot growth decreased.