| At present, Cymbidium·faberi is one of the orchids which possess the greatest economic value in China. Light and water are two of the most important factors. By far, the studies on orchids mainly focus on Phalaenopsis, C.hybridum, oncidum and C.sinense, and the basis studies on C.faberi are few. The changes of photosynthesis and chlorophyⅡfluorescence parameters of C.faberi after natural high light were researched, and after bare rooted treatment the structure, water content, root activity, carbohydrate of the root, and the water content, soluble sugar, SPAD and the chlorophyⅡfluorescence parameters of the leaves were also studied in this article. It is clear that Light and water stress play an important role on the development of C.faberi and recovery status after the stress was removed, which could provide some theory help for management of C.faberi. The results show as follows:1. The photosynthetic character of C.faberi was studied by gas exchange and chlorophyⅡfluorescence during recovery after high light stress in summer. The light compensation point of C. faberi was about 30μmol·m-2·s-1 photosynthetic photon flux and the saturation point about 300μmol·m-2·s-1PPF, which suggested that C .faberi should be a kind of typical shade-acclimated plant. After 1d treatment with high light (600～1300μmol·m-2·s-1), net photosynthetic rate (Pn) and apparent photosynthetic quantum yield (AQY) declined markedly, and light compensation points doubled. Although the light saturation point hardly changed, the maximum Pn at the saturation point decreased by about 60% of the original value. During recovery under room light (100～300μmol·m-2·s-1) after high light stress, the light compensation points decreased and Pn gradually increased, reaching its original level after 8 days.The changes of Pn were in accordance with those of stomatal conductance (Gs). However, further studies showed that intercellular CO2 concentration (Ci) actually increased while Gs declined. The minimal fluorescence intensity (Fo) increased by about 44% after 2 days under room light following high light stress and then decreased. The maximum fluorescence intensity (Fm) and photochemical efficiency (Fv/Fm) decreased obviously after high light stress and then increased gradually during the recovery under room light. Fo,Fm, and Fv/Fm all recovered after 8 days under room light. The results indicated that the photosynthetic apparatus of C. faberi were temporarily hampered by high light that caused the decline of Pn, but fully recovered following several days under room light conditions.2. The contents of water in the different organs of C. faberi were high, which were about 12.6g·g-1DW, 2.3g·g-1DW and 2.9g·g-1DW in the root, old and young leaves respectively. The water content decreased in both of the root and leaves after bare rooted treatment, but it still maintained about 6.9g·g-1DW, 1.9g·g-1DW and 2.4 g·g-1DW after 11 days of treatment. The starch and soluble sugar contents of root in C.faberi were about 255.0mg·g-1DW and 56.2mg·g-1DW respectively, and the soluble sugar levels in the young and old leaves were about 36.8mg·g-1DW and 38.0mg·g-1DW. It could be seen that the soluble sugar levels began to decrease rapidly in the root and the leaves after 5 days treatment, and the starch in roots degraded gradually in the first 7 days, and then its content didn't change. The root activity of the young and old roots declined a lot but still retained about 320.5μg·g-1h-1 and 104.7μg·g-1h-1seperately.3. The values of SPAD declined gradually during the period of bare rooted treatment. The values of Fo rose in both of the old and young leaves, Fv/Fm and Fm values began to decrease rapidly after 5 days treatment.It was also found that the chlorophyll fluorescence parameters could restore gradually during the recovery treatment after 11 days treatment, and they could return to the normal state nearly after two weeks. |
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