| Sabina vulgaris seedlings were used as experimental material in this study. A potexperiment was conducted to study the effects of different shading treatments (shading of0%,25%,50%,75%and90%) on photosynthetic characteristics and chlorophyllfluorescence parameters of S. vulgaris seedlings and study the transformation of pigmentsin xanthophyll cycle and chlorophyll cycle. This paper aims to explore the responsemechanism of S. vulgaris to photoinhibition and definite light protective mechanism of S.vulgaris seedlings. And then provide the theoretical basis for natural regeneration of S.vulgaris. The main results showed as following:(1) With the increase of shading ratio, the net photosynthetic rate (Pn), stomatalconductivity (Gs) and transpiration rate (Tr) decreased in turn, while stomatal CO2concentration (Ci) increased significantly. The principal cause of the reduction inphotosynthesis was attributed to non-stomatal limitation, and the normal growth of S.vulgaris seedlings was affected by the shading of90%. There were correlations between Gsand Trin almost all shading treatments, while poor correlationships between Gsand Pn. Inall shading treatments, water use efficiency (WUE) had an extremely significantcorrelation with Pn, while had no correlation with Tr, so S. vulgaris could improve its WUEin yielding its higher Pnso as to adapt to different light regimes. And there werecorrelations between WUE and Ciin different degrees.With the increase of shading ratio in July, August and September, Pn, Gsand Trof S.vulgaris decreased in turn, and the peak time of Pndiurnal variation in3months weredifferent. The order of Pndaily average in full light treatment and shading50%were:August> July> September, while shading25%was: July> August> September. And theorder of Gsand Trdaily average in3months were: July> August> September. WUE of S.vulgaris was biggest in September when S. vulgaris had low photosynthetic rate and lowtranspiration rate, and WUE decreased with the increase of shading rate in3months. Withthe increase of shading rate, Ciincreased in3months, and Cidaily average of S. vulgaris indifferent treatments appeared no differences with seasons changed. (2) With the increase of shading ratio, chlorophyll a (Chl a), chlorophyll b (Chl b) andthe total chlorophyll content (Chl a+b) increased markedly, while the ratio of chlorophyll ato chlorophyll b (Chl a/b) decreased, and oxidative damage on pigments was caused bystrong light stress at noon in full light treatment. With the increase of shading ratio,antheraxanthin (A), zeaxanthin (Z) and (A+Z) decreased in turn, and the ratio of pigmentof heat dissipation and xanthophyll cycle pool size (V+A+Z) decreased, while violaxanthin(V) increased.(3) With the increase of shading ratio, yields or flux ratios (φPo, Ψoand φEo),phenomenological energy fluxes (ABS/CSm, ETo/CSmand TRo/CSm) and density ofreaction centers (RC/CSm) increased in turn, while absorption flux per CS (ABS/CSo),quantum yield for energy dissipation (φDo) and dissipated energy flux per CS (DIo/CSm)decreased. φPoand performance index (PIABS) of S. vulgaris were minimum in full lightcondition which had maximum light inhibition. Compared with φPo, PIABScould reflect thedegree of light stress more sensitive and better. Under full light condition, photoinhibitionhad a certain degree of damage on donor side of PSII (oxygen evolving complex, OEC) ofS. vulgaris leaves, and also caused the accumulation of receptor side of PSII (QA-), whilereceptor side and donor side of PSII could not been damaged by shading treatments.With the increase of shading ratio in July, August and September, ABS/RC, DIo/RC,TRo/RC and φDodecreased, while φPo, φEo, ψO, Fv/Fo, ABS/CSm(Fm), TRo/CSm, RC/CSmand ETo/CSmincreased. In July, ETo/RC increased with the increase of shading ratio, butshowed a downward trend in August and September. ABS/CSo(Fo) and DIo/CSmdecreased with the increase of shading rate in July and August, and decreased after the firstupward trend in September. With the changes of gradually weakened light intensity in3months, ABS/RC, DIo/RC, ETo/RC and TRo/RC in each treatment almost appeared adownward trend, while Fv/Fo and RC/CSmincreased. From O-J-I-P curves of S. vulgaris at12:00, it’s obvious that donor side of PSII had been damaged by light stress at noon in Julywhen had high photosynthetically active radiation, while donor side of PSII had nophotoinhibition damage in August and September. Moof S. vulgaris in each treatmentappeared no significant differences with seasons changed. The reduction of Smand PQpool were caused by poor light of shading treatments in September and photoinhibition offull light condition in July and August. |
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