*5.9. Statistical Analysis*

All data analyses were conducted using one-way analysis of variance with the ANOVA packages of SPSS® version 17.0 (SPSS Inc., Chicago, IL, USA). The homoscedasticity of the variables was determined using the Levene test. When the *F*-test indicated statistical significance was *p* < 0.05, Duncan's new multiple range test for least significant difference (l.s.d.) was used to determine least significant range between means.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/plants11131688/s1. Figure S1. The spectral distribution of LED lights under different light intensity treatments. Table S1. List of primers for characterizing alfalfa genes (50–30 ) measured under different light treatments. *RCA*, *RbcL*, *RbcS*, *FBPase*, *TK* and *PGK* involve in Rubisco activase, Rubisco large subunit, Rubisco small subunit, Fructose-1,6-bisphosphatase, Transketolase, and Phosphoglycerate kinase, respectively. SS and SPS genes involve in sucrose synthase and sucrose phosphate synthase, respectively. *AGPase*, *SSS*, *SBE*, and *SP* involve in ADP-glucose pyrophosphorylase, soluble starch synthase, starch branching enzyme and starch phosphorylase, respectively. Table S2. Results of one-way ANOVA of effect of light intensity treatment on plant height, stem diameter, abaxial leaf petiole angle, specific leaf weight, shoot dry matter, root dry matter and root to shoot ratio of alfalfa plants. Table S3. Results of one-way ANOVA of effect of light intensity treatment on root length (RL), root surface (RS), root volume (RV), and root diameter (RD) of alfalfa plants. Table S4. Results of one-way ANOVA of effect of light intensity treatment on Chlorophyll a (Chl a), Chlorophyll b (Chl b), carotenoids (Car), Chl a + b, Chl a/b and leaf nitrogen content (LNC) of alfalfa plants. Table S5. Results of one-way ANOVA of effect of light intensity treatment on net photosynthetic rate (*P*n), transpiration rate (*T*r), intercellular CO<sup>2</sup> concentration (*C*<sup>i</sup> ), and stomatal conductance (*g*s) of alfalfa plants. Table S6. Results of one-way ANOVA of effect of light intensity treatment on maximal PSII quantum yield (Fv/Fm), effective PSII quantum yield (ΦPSII), non-photochemical quenching (NPQ) and electron transport rate (ETR) of alfalfa plants. Table S7. Results of one-way ANOVA of effect of light intensity treatment on soluble sugar (SS), sucrose, and starch (St) content of alfalfa plants.

**Author Contributions:** Conceptualization, J.S. and W.T.; methodology, W.T. and H.G.; software and validation, C.Y. and Z.L., investigation, T.W. and S.Z.; formal analysis, Y.Z.; resources, F.M. and Q.T.; data curation, H.S. and Z.L.; writing—original draft preparation, W.T.; writing—review and editing, C.C.B. and W.X.; visualization, J.Y. and X.W.; supervision, J.S. and W.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project has received funding from the China Forage and Grass Research System (CARS-34), First Class Grassland Science Discipline Program of Shandong Province, China (1619002), Natural Science Foundation of Shandong Province (ZR202103040824) and Doctoral Scientific Research Startup of Qingdao Agricultural University (No. 6631120005 and No. 6631120007).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available in the article and supplementary material.

**Conflicts of Interest:** The authors declare that they have no conflicts of interest.
