-->Special Subject: Mangrove and Mangrove Associate

Root biomass and its spatial distribution of Bruguiera gymnorrhiza in the mangrove of Shenzhen Bay, South China

2016/5/4 16:06:55

The native species Bruguiera gymnorrhiza in the Futian Mangrove of Shenzhen Bay, was selected to study the spatial distribution of root biomass. The hierarchical sampling method is adopted. The results showed that root biomass of the B. gymnorrhiza was about 61.23 t·hm^-2; among which, living root biomass accounted for 86.42%, dead root biomass accounted for 13.58%. For the living root biomass, the thick root(>10 mm in diameter)had the highest proportion(84.57%), followed by fine root(2-5 mm, 5.84%), very fine root(<2 mm, 4.94%), and the medium root(5-10 mm, 4.66%). From the tree base to the edge of the canopy, the horizontal distribution of root biomass presented decreasing trend, and the decrement was slowing down, with the root biomass of 77.54 t·hm^-2(the base), 22.88 t·hm^-2(the middle)and 16.15 t·hm^-2(the edge), respectively. In the tree base, > 10 mm in diameter of living root biomass was more than 4 times higher than living root biomass in the middle and the edge. The proportions of < 2 mm living root biomass to the living root biomass increased from the tree base to the canopy edge. Vertical distribution of root biomass was mainly in the lower layer(20-60 cm), with root biomass accounted for 80.89%(the base), 73.41%(the middle)and 71.76%(the edge)for the total root biomass, respectively. The spatial distribution of total root biomass was mainly influenced by the horizontal distance from the tree base(P<0.01), with no significant impact from sediment depth(P > 0.05). In sediments, the value of water content, bulk density, pH and electrical conductivity was(30.66±0.88)%-(35.86±7.59)%,(1.23±0.07)-(1.40±0.00)g·cm^-3,(5.75±1.49)-(7.01±0.50)S·m^-1 and(0.22±0.02)-(0.37±0.12)S·m^-1, respectively. There was no significant relationships between root biomass and sediment properties, such as pH, water content and electrical conductivity(P>0.05). While, significant negative correlations were detected between bulk density and different levels of root biomass, including total root, total live root, total dead root, >10 mm live root and ≥10 mm dead root. It showed that bulk density was one of mean environmental factors influencing the root biomass and its spatial distribution. Biomass is an important basis to evaluate the capacity of carbon sink, this research can provide a basic reference for the further study of underground carbon distribution, reserves and turnover rate in the Futian Mangrove.

Comparison of ionic equilibrium and photosynthesis in introduced Laguncularia racemosa and two native mangrove species in China

2016/5/4 16:06:55

To compare the salt resistance difference of the introduced mangrove and the native mangrove, dynamic variation of accumulation of Na⁺, Cl^–, K⁺, Ca²⁺ and Mg²⁺ in different tissues and photosynthesis were examined in 3-month-old seedlings of the introduced mangrove Laguncularia racemosa and two native species Bruguiera gymnorrhiza and Kandelia obovata under different treatments of NaCl(100, 200, 300 and 400 mmol·L^-1). The results were as follows:(1)The increase in Na⁺ concentration in Kandelia obovata and Bruguiera gymnorrhiza roots was greater than Laguncularia racemosa, while the concentration of Cl^– in Kandelia obovata was higher than that of the other two species in leaves and roots. Thus, Laguncularia racemosa could restrict root absorption of Na⁺, Cl^– and reduce transportation to aerial parts under salt stress of 400 mmol·L^-1.(2)K⁺ concentration in roots and leaves increased in seedlings of all the three mangrove species under high salt stress except that K⁺ concentration in Bruguiera gymnorrhiza leaves non-significantly reduced. The results showed that all the three mangrove species could absorb K⁺ to restrict the damage from Na⁺. The Ca²⁺ concentration decreased in all the three mangrove species under high salt stress, but the decrease in Ca²⁺ concentration in Laguncularia racemosa leave was less than that in Kandelia obovata and Bruguiera gymnorrhiza, indicating that Laguncularia racemosa had stronger ability to prevent the loss of Ca²⁺.(3) Laguncularia racemosa had a greater ability in maintaining Na⁺/K⁺ as well as Na⁺/Ca²⁺ than Kandelia obovata and Bruguiera gymnorrhiza.(4)The net photosynthetic rates of Kandelia obovata and Bruguiera gymnorrhiza under high salt stress reduced while that of the Laguncularia racemosa increased by 54.1%. Taken together, Laguncularia racemosa could restrict root absorption of NaCl, maintain effective Na⁺/K⁺, Na⁺/Ca²⁺, maintaining high net photosynthetic rate. The results indicated that Laguncularia racemosa had higher salt tolerance than Kandelia obovata and Bruguiera gymnorrhiza.

Gas exchange characteristics in the mangrove associate Hibiscus tiliaceus

2016/5/4 16:06:55

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.

Knowledge and existing status of medicinal ethnobotany of mangrove among Jing People in Guangxi

2016/5/4 16:06:55

Jing people is the only national marine fisheries of China. Under the long-term situation surrounded by mangrove plant, they have accumulated a wealth of knowledge and experience on how to use mangrove plants. However, these knowledges and experiences are still being kept under wraps. The aim of this work was to investigate the mangrove medicinal plants from classical mangrove knowledge of Jing ethnic group in Beibu Gulf, South China. We conducted a series of surveys regarding medicinal species composition and their application, and experience for sustainability via ethnobotanical and taxonmical methods. The results showed that a total 15 plant species were recorded belonging to 10 families, these species could provide 49 medicinal services, among which 20 medicinal services had been previously documented, and 29 medical purposes still had not been reported from previous research. The investigation on the level of awareness and dependence on mangrove medicinal ethnobotany showed that the situation of Jing people's dependence on Jing medical practitioner and mangrove medicinal plants were disappearing. In addition, the ecological knowledge with respects to how to harvest mangrove medicinal plants was also analyzed. These findings from this work can broaden our knowledge regarding mangrove medicinal plants from minorities in remote districts, and present a new perspective for the management and sustainable in utilization of mangrove plant resources.