Shading improves initial growth and quality of Parkia multijuga Benth. seedlings

Abstract

During the production of forest seedlings, light quantity can indicate the degree of tolerance of tree species to shading conditions and provide information to obtain seedlings with a higher quality standard. The objective of this study was to evaluate the effect of different levels of shading on the emergence and the quality standard of Parkia multijuga Benth. seedling, a timber species that can be used in landscaping and restoration of degraded areas. The experimental design was completely randomized, consisting of three treatments: full sunlight (control; 2050 µmol m2 s2), 50 (1025 µmol m2 s2), and 70% (615 µmol m2 s2) shading obtained with black polyethylene screens. The results showed that the applied treatments did not significantly influence the emergence percentage. However, under unshaded conditions (i.e., full sunlight), the seeds displayed a higher velocity index and a shorter mean time of seedling emergence. On the other hand, the different levels of shading (50 and 70%) improved the growth performance (e.g., higher shoot height, collar diameter, number of leaves) and quality (e.g., higher Dickson Quality Index (DQI)) of P. multijuga seedlings. Furthermore, seedlings under 50 and 70% shading displayed a significant increase in the total biomass compared to those exposed to the full sunlight condition (243 and 195%, respectively). In addition, the DQI was higher in plants grown at 50 and 70% shading in comparison with the full sunlight treatment (145 and 85%, respectively). The shading level of 50% is recommended for the production of P. multijuga seedlings with the highest quality standard in the nursery beds in Brazilian Amazon.