Effect of Drought Stress on Physiology of Camellia nitidissima Saplings

Potted 3-year-old saplings of Camellia nitidissima Chi were grown under drought stress to monitor the physiological responses of the plants. The results showed that (1)mild drought could lower the net photosynthetic rate (P_n), but a relative water content in soil as low as 20% would not irreversibly damage the photosynthetic function of a 3-year-old C. nitidissima; (2) under a mild or moderate drought condition, the leaf relative water content (LRWC) of the saplings would decline slightly, while the contents of malondialdehyde (MDA), chlorophyll (chl)and soluble sugars (SS) as well as the activity of superoxide dismutase (SOD) would not differ significantly from those of CK; (3) under moderate stress, the peroxidase (POD) activity, carotenoid (Car) content after 15 d of exposure, proline (Pro) at beginning, andsoluble protein (SP) after 15 d were all significantly elevated as compared to CK; and under severe drought, all physiological indicators except Car content were altered significantly. It appeared that mild or moderate drought (when the soil relative water content was reduced to 65% or 40%) indeed affected the physiology of the saplings, but only severe drought (when the soil relative water content became as low as 20%-25%) would permanently change it. Therefore, whenever the water level in soilwas below 25%, appropriate water management and timelywatering could sufficiently avert any serious damages that might incur to the saplings by draught.