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MENG Peng*
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Abstract: To determine the effects of shade on survival rate, relative growth rate (RGR), biomass allocation and photosynthesis characteristics, potted seedlings of shadetolerant Juniperus sabina and shadeintolerant Pinus sylvestris var. mongolica in lownutrient substrate were grown without shade or under a 35%, 65% or 95% reduction of full sunlight over two growing seasons. The results showed that, with decreased light availability, J. sabina growth and survival did not change significantly. Total biomass and RGR increased and then decreased; RGR indicators were positive; and the shoot/root ratio increased significantly. In contrast, the survival rate and growth of P. sylvestris var. mongolica decreased significantly. Total biomass and RGR decreased; the RGR was negative under 95% shade; and the shoot/root ratio decreased significantly. The maximum photochemical efficiency (Fv/Fm) of J. sabina was more sensitive to shade and increased significantly under 35% shade, while the Fv/Fm of P. sylvestris var. mongolica increased significantly until 65% shade. A JIPtest showed that the standardized fluorescence values (Vt) of J. sabina under shade were lower than those under the nonshading treatment (CK) from initial O phase to final P phase. Furthermore, the proportion of electron energy across the QA reaction center to the whole energy captured (ψo), quantum yield of electron transfer (ψEo), size of plastoquinone pool (Sm), plastoquinone pool reduction rate (Sm/Tfm), number of reduced primary quinone acceptors (N), and energy for electron transfer per excited crosssection (ETo/CSo) all increased. The density of reaction centers (RC/CSo) increased, while dissipation per excited crosssection (DIo/CSo) and per reaction center (DIo/RC) decreased, leading to significantly higher performance indexes (PIABS, PICSo, PICSm) under shade than under CK. The Vt of P. sylvestris var. mongolica under shade was higher than under CK from O phase to P phase; however, the above fluorescence parameters were lower or were not significantly different under shade except for the heat dissipation indexes. DIo/RC remained unchanged in P. sylvestris var. mongolica under shade, and the performance indexes (PIABS, PICSo and PICSm) also remained unchanged. The above results indicated that J. sabina was able to maintain high growth and survival under low light intensity by maintaining a positive carbon balance and increasing the proportion of aboveground biomass and electron transfer energy levels during the lightreaction stage. In contrast, P. sylvestris var. mongolica had a low survival rate due to a carbon budget imbalance, and the decreases in proportion of aboveground biomass and electron transfer energy level under shading conditions.
MENG Peng*. Responses of Juniperus sabina and Pinus sylvestris var. mongolica seedlings to shading in low nutrient conditions.[J]. cje.
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URL: https://www.cje.net.cn/EN/abstract/abstract22978.shtml
https://www.cje.net.cn/EN/Y2017/V36/I11/3190