Growth, Physiological, and Biochemical Responses of Tung Tree (Vernicia fordii) Seedlings to Different Light Intensities

in HortScience

As a result of its high photosynthetic efficiency, the tung tree (Vernicia fordii) is a fast-growing heliophile, yielding fruit within 3 years. In addition, tung oil extracted from the fruit seeds is an environmentally friendly paint used widely in China. However, mutual shading inside a tung tree canopy leads to a low yield of fruit because of weak or dead lower branches. In this project, a pot experiment was conducted to understand the growth, physiological, anatomical structure, and biochemical responses of tung trees under various shading levels. Tung tree seedlings were subjected to different light intensities—100% sunlight (no cover), L100; 75% sunlight (25% shading), L75; 50% sunlight (50% shading), L50; and 20% sunlight (80% shading), L20—from June to August. Results indicate that the L75 treatment reduced significantly the net photosynthetic rate (Pn), stomatal conductance (gS), transpiration rate (E), total aboveground and root dry weight (DW), maximum net photosynthetic rate (Amax), and maximum rate of electron transport at saturating irradiance (Jmax) compared with the control, although plant height and leaf area (LA) were not reduced. Lower light intensities (L50 and L20) and longer duration of treatment led to greater reduction in growth, leaf thickness, and photosynthetic potential (Amax and Jmax). Chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll content were increased in the L50 and L20 treatments compared with L100 and L75. There was no significant reduction in the enzyme activities of ribulose-1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate (PEPC) of the seedlings using the L75 treatment; however, lower light intensities (L50 and L20) and longer duration of shade treatment resulted in a significant reduction in enzyme activity. In summary, the results suggest that tung trees have greater photosynthetic activity under high light intensity. Shading, even at 20%, especially for the longer term, reduced photosynthetic efficiency and growth. To prevent growth reduction, tung trees should be grown under full sun with a daily light integral (DLI) of ≈46 mol·m‒2·d‒1, and mutual shading should be avoided by proper spacing and pruning.

Contributor Notes

This work was supported by the National Key R&D Program of China (2017YFD0601304), the Key Research Program of the Education Department of Hunan Province (18A161), and the General Foundation of Central South University of Forestry and Technology (QJ2018001B).

Corresponding authors. E-mail: tanxiaofengcn@126.com or gniu@ag.tamu.edu.

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Article Figures

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    The growth situation of different planting densities of tung tree in the same field. (A) Mature tree spaced at 6 × 6 m have some fruit without shading. (B and C) Mature trees spaced at 4 × 5 m with dead lower branches.

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    Effect of different light levels on assimilation rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate in tung tree seedling leaves. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3). Different capital letters indicate significant differences between July and August. Lowercase letters indicate significant differences among different light treatments in the same month (P ≤ 0.05, Duncan’s multiple range test).

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    Effect of different light levels on (A) water use efficiency and the (B) stomatal limitation value in tung tree seedling leaves. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3). Different capital letters indicate significant differences between July and August. Lowercase letters indicate significant differences among different light treatments in the same month (P ≤ 0.05, Duncan’s multiple range test).

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    Effect of different light levels on relative leaf water content of tung tree seedling leaves. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3). Different capital letters indicate significant differences between July and August. Lowercase letters indicate significant differences among different light treatments within the same month at P ≤ 0.05 according to Duncan’s multiple range test.

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    Effect of different light levels on (A) ribulose-1,5-bisphosphate carboxylase (RuBp) and (B) phosphoenolpyruvate (PEPC) activity in tung tree seedling leaves. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3). Different capital letters indicate significant differences between July and August. Lowercase letters indicate significant differences among different light treatments in the same month (P ≤ 0.05, Duncan’s multiple range test).

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    Net CO2 photosynthetic rate in response to photosynthetic photon flux density in tung tree seedling leaves under different light treatments. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3).

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    Stomatal conductance in response to photosynthetic photon flux density (PPFD) in tung tree seedling leaves grown under different light levels. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3).

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    Net photosynthetic rate in response to CO2 concentration in tung tree seedling leaves under different light levels. L100, 100% light intensity; L75, 75% light intensity; L50, 50% light intensity; L20, 20% light intensity. Data represent the mean ± se (n = 3).

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    Anatomic structure of tung tree seedling leaves under different light levels. (A) One hundred percent light intensity (L100) in July. (B) Seventy-five percent light intensity (L75) in July. (C) Fifty percent light intensity (L50) in July. (D) Twenty percent light intensity (L20) in July. (E) One hundred percent light intensity (L100) in August. (F) Seventy-five percent light intensity (L75) in August. (G) Fifty percent light intensity (L50) in August. (H) Twenty percent light intensity (L20) in August. Bar = 50 µm.

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