Effect of shading on leaf traits and photosynthetic characteristics of Tilia miqueliana container seedlings

This article aims to investigate the effects of different light conditions on leaf traits and photosynthetic physiology of Tilia miqueliana container seedlings.

Taking 1-year-old Tilia miqueliana container seedlings as test materials, this study focuses on the leaf traits, leaf anatomical structure, gas exchange parameters, light response curves, chlorophyll fluorescence indices and photosynthetic pigments of Tilia miqueliana container seedlings under three light conditions, which are full sunlight (CK), 30% shading (T1), and 50% shading (T2).

With the increase of shading intensity, Tilia miqueliana container seedlings showed significant changes in a number of indicators. Leaf length, leaf width, leaf area, leaf water content and leaf fresh weight increased significantly, and reached the maximum under T2 treatment. On the contrary, specific leaf mass decreased significantly with the increase of shading degree, minimum at T2 treatment. In addition, the leaf anatomical structure of Tilia miqueliana seedlings changed with the increase of shading intensity, the thickness of upper and lower epidermis, leaf thickness, epidermal hair density, palisade tissue thickness, spongy tissue thickness, stomatal density, stomatal index and barrier-to-sea ratio all showed a significant decreasing trend, the porosity of the leaves showed an upward trend. In photosynthesis, stomatal conductance, transpiration rate and water use efficiency increased, net photosynthetic rate increased first and then decreased, and intercellular carbon dioxide concentration decreased first and then increased with the increase of shading degree. At the same time, the dark respiration rate and light compensation point decreased gradually, while the maximum net photosynthetic rate increased significantly. The maximum fluorescence, variable fluorescence, maximum photochemical efficiency of PSII, potential photochemical efficiency of PSII and effective photochemical quantum efficiency of PSII all increased with the increase of shading degree, the initial fluorescence was the maximum value under CK treatment, and the values of photochemical quenching coefficient, non-photochemical quenching coefficient and apparent photosynthetic quantum transfer efficiency were first decreased and then decreased, maximum at 30% shade. With the increase of shading intensity, the photosynthetic pigment content increased significantly, but the chlorophyll a/b and carotenoid/chlorophyll ratio decreased significantly.

The seedlings of Tilia miqueliana container seedlings had strong adaptability to low light environment. In mid-August, a shading rate of 50% is more favorable for the growth of one-year-old containerized Tilia miqueliana container seedlings.