Effect of soil temperature on nutrient allocation and mycorrhizas in Scots pine seedlings

We studied the effect of soil temperature on nutrient allocation and mycorrhizal development in seedlings of Scots pine (Pinus sylvestris L.) during the first 9 weeks of the growing season. One-year-old seedlings were grown in Carex-peat from a drained and forested peatland at soil temperatures of 5, 9, 13 and 17 °C under controlled environmental conditions. Fourteen seedlings from each temperature treatment were harvested at intervals of three weeks and the current and previous year's parts of the roots, stems and needles were separated. Mineral nutrient and Al contents in all plant parts were determined and the tips and mycorrhizas of the new roots were counted. Microbial biomass C and N in the growth medium were determined at the end of the experiment. None of the elements studied, except Fe, were taken up from the soil by the seedlings during the first three weeks. Thereafter, the contents of all the elements increased at all soil temperatures except 5 °C. Element concentrations in needles, stems and roots increased with soil temperature. Higher soil temperature greatly increased the number of root tips and mycorrhizas, and the numbers of mycorrhizas increased more than did the length of new roots. Cenococcum geophilum was relatively more abundant at lower soil temperatures (5 and 9 °C) than at higher ones (13 and 17 °C). A trend was observed for decreased microbial biomass C and N in the peat soil at higher soil temperatures at the end of the experiment.