Studies On Photosynthetic Physiology And Ecological Adaptability Of Hibiscus Hamabo

Hibiscus hamabo is a large evergreen tree which distributes in Zhejiang and fujian coastal islands archipelago, with developed root system, strong adaptability, beautiful crown. It has been introduced to Wetland Ecological Station of Hangzhou Bay in 2005. In order to extend utilization, we determined its photosynthetic physiological indices, evaluated its growth status and effect of environmental factors on growth. In addition, we discussed its suitable condition in soil salt content, freshwater content and seawater content by pot experiment. The main conclusions are as follows:(1) Diurnal variation of Pn was two-peak curves both in pool and outside pond, Hangzhou Bay. Daily mean Pn and Pnmax in pool was higher. Path analysis indicated that PAR and Ta were the main environmental factors influencing the net photosynthetic rate, whereas analysis of variance demonstrated that there was not a significant (p>0.05)positive relationship between the PAR, Ca, Ta and TL in the two habitats, however, the positive relationship was significant(p<0.01) for soil salt content between the two habitats. Therefore, oil salt content and tidal disturbance may be the main environmental factors influencing the net photosynthetic rate of Hibiscus hamabo.(2) Pn,Tr and Gs of Hibiscus hamabo increased first and then discreased in 0.80% NaCl treatment period, and WUE was not significantly different from the control. The main reason for decrease in Pn was stomatal limitation in early stage and non-stomatal limitation later. With one-year cutting of Hibiscus hamabo as test materials, this paper studied the effects of different NaCl concentrations (0, 0.2%, 0.4%, 0.6%, 0.8%NaCl) on their leaf pysiological and biochemical characteristics. The results showed that with increase of NaCl concentrations and lengthening of stress time, the electric conductivity,Chl,soluble sugar and free proline increased significantly at the beginning, and then decreased; The POD and SOD activity showed decreasing at the beginning and then increasing, as a whole, they had a higher levels of enzyme activitie in Hibiscus hamabo by salt, maintaining the metabolism balance of reactive oxygen. 20-day salted, the concent of Na+ in the root,stem and leaf of Hibiscus hamabo increased, while the concent of K+ decreased, resulting in the rate of Na~+/K~+ increased, the higher degree of NaCl concentration the more obvious increase. Thus, the high activity of SOD, POD and the appropriate rate of Na~+/K~+ can improve its salt resistance.(3) Within 25d of freshwater and seawater stress, Pn and Tr of Hibiscus hamabo began to decline, WUE maintained a high level, and seawater treatment was significantly lower than freshwater. Experiments were implemented on physiological and biochemical properties of 1-year Hibiscus hamabo cuttings under seawater and freshwater stress treatments. The results indicated that water logging decreased chlorophyII content of the tested seeding; the proline, malondialdehyde concent and the activity of superoxide dismutase increased at beginning and decreased later along with water logging duration; the electric conductirity and the activity of peroxidase increased. Recovery capability of each treatment 20 days later was as follows: freshwater logging>seawater logging. The experiment demonstrated that Hibiscus hamabo was strongly resistant and persistently tolerant to freshwater stress.