Does far-red light affect growth and mycorrhizas of Scots pine seedlings grown in forest soil?

We studied the response of Scots pine (Pinus sylvestris L.) to supplementar y far-red sidelight in seedlings grown in a forest soil substrate without a dditional nutrient supply. Our aim was to determine possible changes in the accumulation and allocation of dry weight and mineral nutrients and the pr esence of mycorrhizas. Half of the seedlings were grown in light conditions simulating reflected far-red light (FR) from neighbouring plants and the o ther half were controls not receiving additional FR. PAR irradiance was kep t constant in both treatments. At the first harvest (41 d of treatment), FR + had no effect on stem height, biomass accumulation or allocation. However , at the end of the experiment (93 d of treatment), an increase in stem ext ension rate and stem dry weight was observed in FR+ seedlings when compared to controls. Both control and treated plants had several morphological typ es of ectomycorrhizas, but no effect of FR+ on the frequency of these morph otypes was observed. Nor was the concentration of ergosterol or estimated m ycorrhizal fungal biomass affected. Nutrients were more responsive to the l ight quality treatment: P concentration in roots and N and P contents in st ems and roots were higher in FR+ plants than in control seedlings. These re sults are in contrast to those of a previous study in which the root system of pine seedlings, which were fertilised and had less developed mycorrhiza s, was reduced by FR+.