| Mangrove plants are usually categorized as true mangroves and mangrove associates on the basis of their distribution in inter-tidal regions. However, the identification of some fringe mangrove species found mainly on the landward transitional zone is controversial. In this research, leaf traits including succulence (water content per unit leaf area), SLA (specific leaf area), mass-based and area-based leaf nitrogen concentration (Nmass and Narea) and elements accumulation (Ca, Mg, K, Na and Cl) in mature leaves were studied for 33 mangrove species, representing all but three of the mangroves in China. Our objective is to determine differences between the two groups and to classify the controversial species. Ultimately this will assist in the management, protection and utilization of mangrove forest. Meanwhile, leaf characteristics (leaf traits, element accumulation and osmotic potential) of Sonneratia caeseolaris grown at different salinities were measured to learn more about the mechanism by which it adapted to saline habitat.1. Leaf characteristics (leaf traits and element accumulation) were suggested as the assistant standard to identify true mangroves and mangrove associates for the first time, which made the standard only based on field investigation combined with the features of physiology and ecology of plants. And according to these standards, mangrove plants in China were classified again.2. 33 mangrove species in China were investigated for their leaf traits and element accumulation for the first time. And the results indicated:(1) There are significant differences (p-value <0.01) between true mangroves and mangrove associates in succulence, SLA, leaf K/Na, leaf Mg, Na, Cl, total elements contents based on the area and Na, Cl concentrations based on the tissue water. For example: True mangroves had Lower SLA and higher succulence than mangrove associates. Leaf Na, Cl, Mg, total elements contents and Na, Cl concentrations in true mangroves were higher than mangrove associates. Additionally, the former had K/Na ratios >1, but the latter had K/Na ratios <1 (except for Hernandia nymphiifolia). (2) There are significant differences (p-value <0.05) between the two groups in Nmass, Narea, leaf Ca, K content and Ca/Na ratios. Most of true mangroves had lower Nmass and higher Narea, and their leaf Ca, K contents were higher than mangrove assocaites. In addition, leaf Ca/Na ratios in the former are lower than those in the latter.(3) The differences in Ca, Mg and K concentrations between true mangroves and mangrove associates were not significant.(4) Leaf Cl content were positively related to succulence for all mangrove species (p-value <0.01). We agree with that it was Na and Cl that induced leaf succulence. And the present study suggested that the leading factor is Cl not Na.3. We didn't find out any significant changes in leaf traits of Sonneratia caeseolaris grown at different salinities. Leaf Na, Cl, Mg concentrations increased with the increasing of salinity, and K concentration decreased significantly associated with Na accumulation in leaves. However, Ca concentration showed little change. Furthermore, leaf osmotic potential decreased because of the increased osmolality and the contribution of inorganic ions to osmotic potential declined slightly as external salinity increased from 3.29‰to 12.89‰.4. According to field investigation of distribution combined with the significant differences in leaf characteristics between true mangroves and mangrove associates, 8 controversial mangrove species are identified as follows: Heritiera littoralis, Excoecaria agallocha, Acrostichum aureum and Acrostichum speciosum are classified as mangrove associates, while Xylocarpus granatum, Acanthus ilicifolius, Acanthus ebrecteatus and Pemphis acidula are classified as true mangroves.5.Clerodendrum inerme needs further research because of its great differences in leaf characteristics from other mangrove associates.
|
PDF Full Text Request