Syntrichia caninervis Mitt. is the dominant species in the moss crusts of the Gurbantunggut Desert, Northwestern China. We experimented with this species under controlled environmental conditions. Modulated chlorophyll (Chl) fluorescence was used to test the speed of recovery as evidenced by the time course of photosynthetic activity following remoistening. Transmission electron microscopy was used to explore the cytological characteristics of the leaf cells. Minimum and maximum fluorescence (F0 and FM) and photosynthetic yield (FV/FM) of photosystem II (PSII) recovered quickly when shoots were remoistened in the dark. This was especially the case of FV/FM; within the first minute of remoistening this reached 90% or more of the value attained after 30 min. These physiological changes were closely paralleled by cytological changes that indicated no damage to membranes or organelles. Correlation analysis showed that Chl fluorescence decreased both above and below a narrow moisture optimum. Our results underline the capability of S. caninervis to photosynthesize after remoistening. Utilizing precipitation events such as dew, fog, rain, and melting snow allows S. caninervis to survive and grow in a harsh desert environment. and J. Zhang ... [et al.].
In this paper, photosynthetic characteristics of green leaves (GL) and green pseudobulbs (GPSB) of C3 orchid Oncidium Golden Wish were first studied. Light saturation for photosynthesis and maximum photosynthetic rates (Pmax) were significantly higher in GL than in GPSB. The results of the optimal PSII quantum yield (Fv/Fm ratio), electron transport rate (ETR), the effective photochemical quantum yield (ΔF/Fm') and nonphotochemical quenching (NPQ) of Chl fluorescence revealed that GPSB had lower light utilization than that of GL. Significantly higher photosynthetic pigments were found in GL than in GPSB. Alteration of source/sink ratio had no impact on all photosynthetic parameters for both GL and GPSB after a short term of 3 days or even a long term of 2 weeks of treatments although there were significant decreases in GL carbohydrate concentration of GL-darkened plants by the end of the day. However, decreases of all photosynthetic parameters of GL were observed in GL-darkened plants after 4 weeks of treatment compared to those of fully illuminated (FI) and GPSB-darkened plants. These results indicate that the level of carbohydrates in GL plays an important role in regulating their photosynthesis. Due to their lower photosynthetic capacities, GPSB function mainly as sinks. Darkening GPSB up to 2 weeks did not affect their own Pmax and the Pmax of GL and thus, did not result in significant decreases of total carbohydrate concentration of GPSB. As GPSB store a large amount of carbohydrates, it could also act as a source when the level of carbohydrates decreased. Thus, GL could depend on GPSB carbohydrates to regulate their photosynthesis when their source capacity was removed. However, 4 weeks after treatments, photosynthetic capacities of GL were significantly lower in GL- and GPSB-darkened plants than in FI plants, which could be due to the lower total soluble and insoluble sugar concentrations of both GL and GPSB in these plants. and J. He, B. H. G. Tan, L. Qin.