Producing high-quality container-grown Scots pine seedlings: the role of substrate composition and plant growth regulators

Abstract

Effective cultivation of Scots pine ( Pinus sylvestris ) planting material with a closed-root system largely depends on the optimal substrate composition, which provides favourable conditions for seed germination and seedling growth. This study presents the results of analysing the impact of different substrate modifications on seed germination, seedling condition, seedling height growth and root system development. The research covered five substrate variants: 3 two-component substrates (bark:peat in ratios of 2:1, 1:1 and 1:2) and 2 three-component substrates (bark:peat:forest soil 1:1:1; bark:peat:sawdust compost 1:1:1). It was found that the first seedlings emerged 15 days after sowing in all experimental variants, and the average germination rate was 69.75%. The best germination and germination energy were observed in the substrate dominated by peat (1:2). The seedlings grown in substrates with sawdust compost and a balanced component ratio showed the best biometric performance overall. Seedling height growth depended on the substrate composition: the highest values (5.5 cm) were recorded in variants with a higher content of peat and sawdust compost, whereas compacted forest soil slowed down their growth. Spring inventory showed that the average seedling height was observed in substrate 3 (with the highest peat content) and substrate 5 (which included sawdust compost). The study evaluates the effects of plant growth regulators Stimpo, Epin Extra, Humat Ultra and Megafol on plant morphophysiological parameters. The application of these biostimulants enhanced growth processes, increased tolerance to abiotic stress factors and improved adaptive responses. Epin Extra demonstrated a pronounced anti-stress effect, Humat Ultra stimulated root system development and nutrient uptake, Megafol intensified metabolic activity under stress conditions, while Stimpo promoted seed germination and early plant growth. The combined use of these regulators resulted in improved plant productivity and viability. The use of growth regulators significantly increased the biometric parameters of seedlings, particularly root collar diameter and biomass. The highest efficacy was observed for Megafol (p < 0.01), while Stimpo and Humate Ultra also resulted in significant improvements in these parameters. Epin Extra demonstrated a moderate but statistically significant effect (p < 0.05). The results obtained indicate the advisability of using Megafol and Stimpo to intensify the growth processes of seedlings. The most effective growing media for Scots pine seedlings are a two-component bark–peat mixture (1:2) and a three-component bark–peat–sawdust mixture (1:1:1), which yield the highest germination rates and the best biometric indicators. Other options, particularly those incorporating forest soil, proved to be less effective.