[Wind-attenuation effect of Sonneratia apetala and Kandelia obovata plantations].

A field monitoring was conducted to examine the wind-attenuation effect of mangrove plantations at the Sanjiang Bay of Dongzhai Harbor, Hainan Province of South China. The wind speed and wind direction were measured at a site 50 m away from the offshore forest fringes of Sonneratia apetala and Kandelia obovata plantations and 2 m above the ground. Both the S. apetala and the K. obovata plantations had obvious effect in attenuating the speed of the wind from northerly to the shore, with the mean wind speed decreased by > 85% and the better effect of K. obovata plantation. With the increase of the wind speed, the wind-attenuation effect of the plantations presented a trend of decreasing first and remained stable then. At 50 m away from the offshore forest fringe of S. apetala plantation, the wind-attenuation rate was higher than 89.8% when the mean wind speed was lower than 5 m x s(-1), tended to be stable when the mean wind speed was 10 m x s(-1), and turned to be 58.9%-63.6% when the mean wind speed was higher than 15 m x s(-1). The S. apetala plantation had better wind attenuation effect in warmer season than in colder season. Under the extremely adverse weather like typhoon, the mean wind speed and extreme wind speed at 50 m away from the offshore forest fringe of S. apetala plantation were decreased by 59.4% and 53.2%, respectively.

Physiological responses of mangrove Sonneratia apetala Buch-Ham plant to wastewater nutrients and heavy metals.

Mangroves play an important role for removing nutrients, heavy metals, and other pollutants in wetland ecosystems. This study investigated the physiological responses of a mangrove plant (i.e., Sonneratia apetala Buch-Ham) to different wastewater pollution levels. Four different treatments, namely three concentration levels (i.e., normal, five-time-greater than normal, and ten-time-greater than normal) of wastewaters and one control (i.e., salted water), were used to grow the mangrove plants. Results showed that the height and biomass of the plant increased with wastewater pollution levels. No significant differences in root and catalase activities were observed among different treatments, whereas the increases in peroxidase and superoxide dismutase activities were attributed to the need for detoxification. In general, leaf chlorophyll content increased with wastewater pollution levels due to the increase in nutrient contents.

[Adaptability of mangrove Avicennia marina seedlings to simulated tide-inundated times].

A laboratory test on the effects of differents simulated tide-inundated times with 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 h x d(-1) on the growth of Avicennia marina seedlings was conducted. The ten growth information indices including chlorophyll, root vigor, growth, biomass and photosynthetic rate were mensurated. The principal components analysis was made combining the ten growth information indices. The 210 d experimental results showed that the chlorophyll, root vigor, growth and biomass would rise first and then fall as the extension of the inundate time; and they changed suddenly at the threshold inundate time 16 h x d(-1). The growth and biomass of Avicennia marina seedlings with more than 16 hours tide-inundated time per day were less than them with no more than 16 hours tide-inundated time per day. The maximum value of stem increment each month, leaf blade increment each month, dry weight of stem, dry weight of root and total biomass were under the 10 hours tide-inundated time per day. It concluded that Avicennia marina seedlings would grow adaptively with less than 16 hours tide-inundated time per day, 8-12 hours of tide-inundated time per day is the most suitable for the growth of Avicennia marina seedlings, while 16 h x d(-1) is a critical tide-inundated time when the plant responded to be obviously inadaptable.