Photooxidation in Leaves of Facultative CAM Plant Sedum spectabile at C_3 and CAM Mode

The switch from C-3 to CAM pathway was induced by water stress in a C-3/CAM intermediate plant Sedum spectabile Boreau. Typical CAM criteria were observed upon 15 d of withholding water. Leaf delta(13)C value (-%) and water content showed a linear correlation fashion. Chlorophyll fluorescence parameters and antioxidative capacity were altered by water stress. Phi(PSII) and q(P) were reduced by 50% and 34% of the control, respectively, while NPQ rose ca. 180%. SOD activity and ability to scavenge DPPH. free radical went down but membrane permeability changed slightly. However, when an additional photooxidation by MV with high PPFD was carried out with leaf discs from watered (C-3 mode) and drought plants (CAM mode), q(P) and Phi(PSII) in leaves at induced CAM mode stage continuously decreased to a very low level. High 1 - q(P) value (0.86) and 1 - q(P)/NPQ ratio (>1) indicated the presence of high reduction state and unbalance of light energy budget. Together with the marked loss of membrane integral, it was evidenced that photooxidative damage was more serious in the induced CAM mode than in the C-3 mode. No advantage of photooxidation tolerance was found at the induced CAM expression stage of the facultative CAM plant, as compared with its C-3 mode stage, and also with the constitutive CAM plants reported previously. The differences in photooxidation sensitivity between the inducible CAM expressing plant and the constitutive CAM plant were discussed.

Influence of Sedum Spectabile on Cd Concentration in Soil and Runoff

To research how planting Sedum spectabile affects Cd loss, in this experiment, the impact of soil pollution level (low, medium, high), rainfall intensity (30, 60, 90 mm·h-1), and slope (6°, 12°, 18°, 24°) on Cd concentration in soil and runoff after planting Sedum spectabile are investigating using an indoor artificial rainfall simulation method. The results showed that: 1) The mean values of agricultural soils in the study area reached 38.52 and 1073.28 mg·kg-1 for Cd and Zn, respectively, which were 176.70 and 11.96 times higher than the background values of soil environment in southern Yunnan. 2) The decrease of total Cd in the soil after planting Sedum spectabile ranged from 17.52% to 31.09%, and the decrease of effective state Cd ranged from 14.36% to 21.81%. The higher the pollution level, the more significant the decrease of effective state Cd. 3) After 120 days of planting, the Cd concentration in runoff decreased between 22.40% and 89.23% compared to 15 days, with the more significant decrease in low Cd pollution, 90 mm·h-1 rainfall, medium Cd pollution, 30 mm·h-1 rainfall, and high Cd pollution, 90 mm·h-1, reaching 81.14% - 87.43%, 82.21% - 89.00%, and 37.57% - 89.23%. 4) The pollution level and rainfall intensity were significantly and positively correlated with Cd concentration in runoff at 15 and 120 days of planting Sedum spectabile, with correlation coefficients of 0.498, 0.641, and 0.435, 0.464. Research shows that planting Sedum spectabile can reduce the Cd concentration in soil and runoff, which is essential for the remediation of Cd-contaminated farmland.