Comparisons Of Element Distribution Characteristics And Salt Tolerance Between True Mangroves And Mangrove Associates

Mangroves are halophytes, mainly tree species that grow in tidal saline wetlands along tropical and subtropical coasts. They are usually categorized as true mangrove plants and mangrove associates. Also there have some standards to distinguish these two kinds of plants, there are still great differences in the understanding of these standards. So there is still much controversy about some mangrove species. The distribution of K, Na, Cl, Ca, Mg in different organs of sixteen unanimously true mangrove plants, eight mangrove associates and eight controversial species were studied in this paper. The results indicated that salt distribution in true mangrove plants and mangrove associates was significantly different.1. The Na and Cl content in roots of different diameters was significantly higher in true mangrove plants than that in mangrove associates. And in true mangrove plants, the root Cl content increased but later decreased with the increase of diameters, the mangrove associates didn't.2. For most mangrove plants, salt content in underground organs was greater than that in overground organs; Furthermore, salt content in overground organs was significantly greater in true mangrove plants than that in mangrove associates, but mangrove associates Clerodendrum inerme and Hernandia nymphiifolia were an exception, they also had very high salt content in overground organs.3. There was no difference of K content in underground organs between true mangrove plants and mangrove associates, but K content in overground organs of mangrove associates was significantly higher than in true mangrove plants.4. The K:Na ratios in roots and overground organs (except trunk) of true mangrove plants were significantly lower than mangrove associates. The K:Na transport selectivity ratios were also higher in mangrove associates (C. inerme and H. nymphiifolia were excluded).5. There were some differences of element content among species in true mangrove plants; In mangrove associates the Ca, K content was higher than Na, Mg in different organs.From the characteristics of salt distribution, Acrostichum aureum, A. speciosum, Excoecaria agallocha, Heritiera littoralis are classified as mangrove associate, while Acanthus ilicifolius, A. ebracteatus, Xylocarpus granatum are classified as true mangrove plants.