# Effects of Different Light Intensities on the Growth and Photosynthetic Physiological Characteristics of Cremastra appendiculata (D. Don) Makino Seedlings

## TL;DR

This study finds that low light intensity promotes better growth and photosynthesis in rare orchid seedlings compared to higher light conditions.

## Contribution

The study identifies low light as optimal for C. appendiculata seedling growth and reveals physiological mechanisms behind this preference.

## Key findings

- Low light increased plant height, leaf area, and biomass by 48%, 41%, and 50% compared to high light.
- Low light enhanced chlorophyll content and improved photosynthetic efficiency and PSII performance.
- Leaf structure under low light showed shade-leaf characteristics with tightly arranged cells and intact mesophyll.

## Abstract

Cremastra appendiculata (D. Don) Makino, a rare orchid prized for its ornamental and medicinal value, exhibits high sensitivity to light conditions during the seedling stage. To identify optimal light intensity for promoting seedling growth and elucidate the underlying physiological mechanisms, this study exposed C. appendiculata seedlings to three light treatments: low light (LL, 80% shading, 300–350 µmol·m−2·s−1), medium light (ML, 60% shading, 600–650 µmol·m−2·s−1), and high light (HL, 30% shading, 900–1000 µmol·m−2·s−1). Growth and photosynthetic physiological parameters were measured to investigate the regulatory effects of light intensity. Results showed that under LL treatment, plant height, leaf area, and total biomass were significantly higher than those under HL treatment, increasing by 48%, 41%, and 50%, respectively. Leaf anatomical structure under LL displayed tightly arranged epidermal cells and intact mesophyll organization, consistent with typical shade-leaf characteristics. Chlorophyll content analysis revealed that chlorophyll a, chlorophyll b, and total chlorophyll under LL increased significantly by 75%, 35%, and 50%, respectively, compared to HL. Moreover, net photosynthetic rate peaked under LL, exceeding ML and HL by 28% and 17%, respectively. Chlorophyll fluorescence analysis further indicated that LL treatment optimized PSII performance, enhancing maximum photochemical efficiency, photosynthetic performance index, and electron transport rate per reaction center, while maintaining low thermal dissipation, indicating superior light capture and conversion efficiency. In summary, within the experimental gradient established in this study, the LL treatment represents the optimal light environment for the growth of C. appendiculata seedlings. By synergistically promoting plant morphological development, optimizing leaf structure, enhancing photosynthetic pigment content, and improving Photosystem II performance, this treatment facilitates efficient biomass accumulation. These findings provide a critical theoretical basis for the light environment management in both the conservation and artificial propagation of C. appendiculata.