Growth dynamics and mycorrhizas of Norway spruce ( Picea abies) seedlings in relation to boron supply

Abstract

The effects of three boron levels on the growth dynamics and ectomycorrhizas of seedlings of Norway spruce [Picea abies (L.) Karst.] were studied in a growth room experiment. The seedlings were grown in forest humus mixed with quartz sand for 16 weeks. The B treatment was applied in the nutrient solution. Stem height, dry weight, number of root tips, mycorrhizas as well as B and N concentrations in the seedlings were monitored in sequential harvests. By the last harvest, in week 16, needle B concentrations were 6.6 mg kg–1 at the lowest B level and 17.5 mg kg–1 and 26.5 mg kg–1 at the two higher levels. Boron slightly increased the stem height and the total dry weight, but did not affect N content of the seedlings. Low internal B reduced the number of root tips and mycorrhizas as well as mycorrhizal percentage and root dry weight, which indicates the importance of B for root growth in Norway spruce seedlings. The seedlings grown with adequate internal B had more root tips than those receiving the two lower B treatments as early as week 9, when needle B concentrations at the lowest B supply were 16.0–17.3 mg kg–1, which has previously been considered a sufficient B level. Therefore, the critical needle B concentrations should perhaps be re-examined.