Effect of artificial shading on seed germination, survival, and growth and of one-year-old seedlings of Paulownia fortunei

Paulownia fortunei is from industrial and multipurpose introduced tree species that has been considered for wood farming, agroforestry practices and seedling production in northern Iran, especially in Golestan province, due to its suitable growth properties and productive traits. Knowing the factors affecting the germination and early growth of this species can provide the possibility of improving the quality of seedlings produced in forest nurseries and thus increases the feasibility of success in planting practices of this species. Therefore, in terms of the importance of studying the reaction of P fortune against different light intensity control treatments, the present study tries to investigate the effect of artificial shading on the performance of this plant in the germination and seedling stages.

Thanks to the inherent differences in plant needs and responses in the stages of germination and early growth, in this study, two independent experiments were designed and performed to achieve the research objectives. Aimed to investigate the effects of artificial shading treatments on performance of this plant, two independent experiments were conducted at germination and seedling stages. In the first experiment, using a completely randomized design, seed germination features were studied under three shading (25%, 50% and 75%) and one control (without shade) treatments in the laboratory (Temperature of 25 °C and 70% relative humidity in a Germinator) conditions. In this experiment, seed germination was recorded for 3 weeks and at the end of the period, the growth traits of the sprouted seedlings were examined. Based on the information obtained, seed germination traits including germination speed (GS), germination energy (GE), peak value (PV), mean daily germination (MDG) and germination value (GV) as well as seed vigor index (VI) and length of shoot and root of sprouted seedlings were measured. In the second experiment, the growth and survival of 44 potted p fortunei seedlings under four treatments (including control, 25%, 50% and 75% shading) were studied in the first growing season for 5 months, from the beginning of July to the end of November. At the end of the growing season, all seedlings were taken out of the pot and length, diameter and dry weight of stem, leaf area and length, dry weight of main and secondary roots were measured after separating the shoot and root. One-way analysis of variance and Duncan's test were used for statistical comparing of treatments at 5% probability level.

The results showed that GP, GS, MDG, and VI did not affected by shading treatments, However, the negative effects of shading treatments, especially in 50% and 75% shading levels on GV and PV were significant. Artificial shading did not affect first year seedling survival, so that all of seedlings were survived under all treatments. Also, the results showed that under 50% and 75% shading treatments, stem length, stem diameter, stem dry weight, number and area of leaves were significantly higher than control and 25% treatments. Additionally, under 50% shading treatment, secondary root dry weight and total dry weight of seedlings were significantly upper than other treatments.

Seed germination and first year survival of P. fortunei did not so sensitive to light intensity, but controlling light intensity using artificial shading improve seedling quality traits of this species. Hence, use of 50% shading treatments can be proposed in nurseries of this species after initial stages of germination and seedling establishment.