[Effects of different light qualities on field-grown Epimedium pubescens]

The study investigated the effects of different light qualities on the photosynthetic parameters, yield, and bioactive chemical content of Epimedium pubescens under field conditions and identified the optimal light quality for cultivation, aiming to provide a theoretical basis for the application of different light qualities in field production. The variety "Guitong Roumao No.1" was planted with five treatments: black(control), blue, red, yellow, and green shade nets, under 75% shading rate. Dynamic changes in chlorophyll content, photosynthetic parameters, and bioactive chemicals were measured on days 60 and 120. On day 120, the dry weights of the aerial and underground parts were measured, and the root-to-shoot ratio was calculated. The effects of light quality were comprehensively evaluated by principal component analysis(PCA). The results demonstrated that compared with the black net, the blue net increased the total dry weight by 36.28%(P<0.05), with a 13.53% increase in the aerial part. In contrast, the red net decreased the total dry weight by 35.74%(P<0.05), with a 48.53% decrease in the aerial part. No significant differences in total dry weight were observed between the yellow/green nets and the black net. The blue net maintained the highest net photosynthetic rate(P_n) and maximum net photosynthetic rate(A_(max)) on day 120. Under the red net, P_n significantly decreased due to reduced light capture capacity(declines in apparent quantum efficiency [AQE] and chlorophyll relative content [SPAD]) and inhibition of Rubisco activity and electron transport processes in the Calvin cycle. No significant difference in A_(max) was detected under the yellow and green nets relative to the black net. The total content of bioactive chemicals under the blue net on day 120 was higher than that under the black net and showed no decline compared with that on day 60. PCA integrating photosynthetic characteristics, yield, and bioactive chemical content demonstrated that the blue net had a greater overall promoting effect than the black net, while the other colored shade nets had lesser effects than the black net. These findings indicate that the blue net can maintain high photosynthetic efficiency, promote dry matter accumulation, and effectively inhibit the decline in bioactive chemical content. The use of blue shade nets is recommended for the field cultivation of E. pubescens.