Effects of red and blue LED light sources on the growth of SRPs
The light treatment had significant (p < 0.001) effects on the shoot length and root differentiation of the SRPs. The shoot length of SRPs was significantly (p < 0.05) increased under the blue light treatment, while the needles were light green in contrast to the CK treatment. Additionally, the root differentiation was significantly (p < 0.05) promoted under the R, 7R3B, and 8R2B treatments (Fig. 4). With further statistical analysis, the greatest shoot length (3.56 cm) was obtained under the blue light treatment (Fig. 4 A). In terms of root differentiation, the total length of roots, their volume, and the number of root tips all reached the peak under the 8R2B treatment (Figs. 4 B, D, E). However, the root surface area and average diameter reached their peak under the R treatment (Fig. 4 C, F). In general, the blue light promoted the longitudinal growth of the shoots, whereas the red light was beneficial for root development. In addition, the optimal combination for the enhancement of the SRP was 8R2B.