Photosynthetic responses of Halophila ovalis (R. Br.) Hook. f. to osmotic stress

摘要: Chlorophyll fluorescence was used to monitor the onset, development and recovery from hyper- hypo-osmotic stress effects of seagrass, Halophila ovalis (R. Br.) Hook. f. H. able tolerate rapid transfer normal (35 ppt) seawater salinities 25% 150% without significant photosynthetic symptoms. Exposure fresh water caused acute stress: within 24 h, all specimens exposed showed substantial damage, after 4 days were photosynthetically inactive. Hyper-osmotic conditions more severe responses, with tolerating seawater, whereas sudden exposure 200% 250% irreparable damage 96 h. The severity extreme osmotic responses light-dependent, as a similar level in darkness apparently resulted less damage. Recovery limited 50% treatments, treatment survived but did not recover control level. Fresh water, treatments completely quenched photosynthesis during 5-day experimental period, and, therefore, possible. Although demonstrated, premature senescence entire leaf petiole. Photosynthetic pigments also affected by stress, partially light-dependent. thus confirmed chlorophyll responses.