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The restoration and reconstruction of mangrove wetland ecosystem is one of the key research fields in ecological restoration in the coastal zone of South China. In order to reveal the physiological and ecological strategies to light conditions of mangrove species, the characteristics of leaf soluble protein contents and activities of antioxidant enzymes in seedlings of eight mangrove species(Sonneratia apetala, Kandelia obovata, Bruguiera gymnorhiza, Aegiceras corniculatum, Acanthus ilicifolius, Acrostichum aureum, Heritiera littoralis and Hibiscus tiliaceus)under different light intensity treatments(100%, 45%, 30%, and 10% of natural light intensity)were studied using shading control experiment. The results were as follows:(1)Low light intensities had little effect on the leaf soluble protein contents of Bruguiera gymnorhiza, Acanthus ilicifolius and Acrostichum aureum, whereas the other five species showed a decreasing trend of leaf soluble protein contents with the decline in light intensity.(2)The activities of superoxide dismutase(SOD)and ascorbate peroxidase(APX)in the leaves of Bruguiera gymnorhiza, Acanthus ilicifolius and Acrostichum aureum under 10% of natural light intensity treatment had no significant differences compared with the control, while the other five mangrove species showed a decreasing trend of all the five antioxidant enzyme activities. In conclusion, the results indicate that Bruguiera gymnorhiza, Acanthus ilicifolius and Acrostichum aureum are suitable to be planted under the forest with high canopy density, while Sonneratia apetala, Kandelia obovata, Aegiceras corniculatum, Heritiera littoralis, Hibiscus tiliaceus are suitable to be planted under the forest with lower canopy density or planted as middle and upper layer tree species in mangrove. The results of this study provide theoretical guidance for the optimal allocation of artificial mangrove communities. [ABSTRACT FROM AUTHOR]

Mangrove associates are a category of plants that can grow and reproduce on both intertidal coastal zones and land. As subtropical coastal zones are characterized by high sun light and temperature, how mangrove associates adapt to such an environment is an important issue. Some researches show that mangrove associates are similar to land plant as well as thalassophyte in certain morphological structures and biochemical characteristics. However, there are few studies focusing on plant physiological characteristics of mangrove associates, especially in leaf gas exchange characteristics. Hibiscus tiliaceus(Malvaceae)is a pantropical mangrove associate that usually occurs in coastal zones. It is widely used for the conservation of sea banks, architecture and medicine. In order to disentangle the photosynthetic physiological mechanims underlying its habitat adaptation to high light and temperature under south subtropical climate, leaf gas exchange characteristics of H. tiliaceus were measured using LI-6400 portable photosynthesis system(Li-Cor Inc, USA)at Mangrove Natural Reserve of Qi'ao Island of Zhuhai City, Guangdong Province during July and August of 2013. The nature reserve(22°23'40'' N, 113°36'40'' E)is characterized by a typical south subtropical monsoon climate. The diurnal changes in photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2 concentration(Ci)and transpiration rate(E)in H. tiliaceus all exhibited a mono-peak modal, and the peak value of Pn occurring at noon was around 26.8 μmol CO2 · m-2 · s-1 without obvious photoinhibition during the daytime. The high photosynthetic rate in H. tiliaceus was associated with high stomatal conductance, which was probably related to anatomical features of leaves, such as high stomatal density and dense trichomes in the lower leaf epidermis. Analysis of light response curves revealed that its light saturation point was 800 μmol photons·m-2 ·s-1 and its light compensation point was 26 μmol photons·m-2 ·s-1. The net photosynthesis at saturating irradiances was high at 27.8 μmol CO2 · m-2 · s-1. These photosynthesis parameters, along with high daily mean photosynthetic rate(19.6 μmol CO2 · m-2 · s-1)in H. tiliaceus suggested that this mangrove associate was characterized as a typical sun plant species. The results showed that the fast growth of H. tiliaceus might be attributed to its high and stable photosynthetic capacity, thus providing basic data for further revealing the eco-physiological mechanism underlying habitat adaptation of H. tiliaceus and other mangrove associates to coastal environment with high temperature and high light in summer. These results can also provide theoretical supports for its planting and reforestation practices. [ABSTRACT FROM AUTHOR]