Abstract: Light is the main environmental factor for plants to capture energy. Severely low light conditions can reduce the photosynthetic efficiency of plants leading to limited plant growth, and excess light can also hinder plant growth and development. An experiment was undertaken to investigate changes in photosynthesis parameters and antioxidant characteristics in Pueraria lobata under different shading treatments: control (100% natural light, T₁), mild shade (75% natural light, T₂) and moderate shade (50% natural light, T₃). Seedlings of P. lobata were collected and grown in a nursery, and then healthy seedlings of uniform-size seedlings were transferred to the shade shed when seedlings had 8 or 9 leaves. Each treatment was replicated 6 times. It was found that chlorophyll a, chlorophyll b, carotenoid content and total photosynthetic pigment content were increased with the increase of shading degree, while the change of chlorophyll a/b was opposite; The net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r) of P. lobata decreased with increased shading, while the intercellular CO₂ concentration (C_i) was increased. The chlorophyll fluorescence parameters of minimal fluorescence (F₀), maximal fluorescence (F_m), variable fluorescence (F_v), F_v/F₀, F_v/F_m and PSII actual photochemical efficiency (Φ_PSⅡ) of P. lobata were increased with increased shading. Meanwhile, soluble sugar, soluble protein, and free amino acid levels in P. lobata leaves decreased with increased shading degree, while malondialdehyde levels and electrical conductivity increased. The antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) decreased with increased shading. The results indicate that low light levels cause stress to P. lobata and it is necessary to avoid low light stress when P. lobata seedlings are establishing. The mechanisms of shading effects on photosynthetic and antioxidant systems of P. lobata and on its growth in different shading treatments, need further research.

Key words: Pueraria lobata, shade, low light, chlorophyll fluorescence, photosynthetic rate, physiological characteristics