Relationship between sediment conditions and mangrove Rhizophora apiculataseedling growth and nutrient status

The growth rate and nutritional status of Rhizophora apiculata seedlings we re analyzed across mangrove stands with different sediment composition in T he Philippines and Southern Thailand. Plant growth differed 10-fold and the production of new leaves, roots and branches varied between 50- and 100-fo ld across sites. Most (>60%) of the variance in mangrove growth rate across systems could be accounted for by differences in the nutrient concentratio n of the leaves, which was in turn related to the interstitial nutrient con centration and the silt plus clay content of the sediments. Nutrient-poor c oarse sediments were characteristic of mangroves located in the mouths of r ivers draining small watersheds, while sediments at the mouths of large riv ers had high silt, clay, and nutrient contents, thus allowing the developme nt of nutrient-sufficient, fast-growing R. apiculata seedlings. The growth of R. apiculata seedlings increased significantly when the plants grew adja cent to rivers draining areas >10 km(2). The results provide evidence that growth of R. apiculata seedlings at the edge of the progressing mangrove fo rests is often nutrient limited, and that the extent of nutrient. Limitatio n depends on the delivery of silt and nutrients from the rivers. The coasta l zones adjacent to small (<10 km(2)) drainage areas seem unsuitable to sup port adequate growth of R. apiculata seedlings, and afforestation programme s should, therefore, target mud flats adjacent to large rivers instead.