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Interactive effects of drought and shading on Torreya grandis seedlings: physiological and growth responses

Lin, Jianhong, Zhang, Rui, Hu, Yuanyuan, Song, Yang, Hänninen, Heikki, Wu, Jiasheng
Trees 2019 v.33 no.3 pp. 951-961
Torreya grandis, biomass production, chlorophyll, drought, field capacity, photosynthesis, proline, seedlings, shade, solar radiation, trees, water stress
KEY MESSAGE: Moderate shading is optimal for the growth of Torreya grandis seedlings during drought. Light and water are two important environmental factors affecting tree seedling traits and regulating seedling survival and growth, but the effects of light on seedlings under drought remain poorly understood. The purpose of the present study was to examine the interactive effects of light and drought on second-year Torreya grandis seedlings. A pot experiment was conducted with 240 seedlings using four shading treatments (0%, 50%, 75%, and 90% reduction of full sunlight, respectively) and two watering treatments (well watered = 75% of field capacity, drought treatment = 30% of field capacity). In drought-treated seedlings, photosynthesis was inhibited along with decreased contents of chlorophyll and high contents of reactive oxygen, and biomass accumulation was reduced, as compared to well-watered seedlings. Seedlings grown under moderate shade (50% and 75%) showed highest biomass and photosynthetic rate both in well-watered and drought treatments. Similarly, the differences between well-watered and drought-treated seedlings for stress metabolism parameters (i.e., contents of proline and soluble protein) were also lower under moderate shading, indicating drought stress was alleviated by the shading. The chlorophyll contents and the photosynthetic rate were higher in the seedlings under moderate shading than in those in full sunlight, contributing to a higher biomass in the former. These results suggest that moderate shading can effectively prevent stress caused to the Torreya grandis seedlings by excess light and can also alleviate the damage caused to them by drought.