Nutrient and mass allocation of South-east Asian seagrasses

Differences in ramet size (i.e. the mass of a shoot with its share of leaves, rhizome and roots) and allocation of mass and nutrients to different ramet components were quantified based on a comparative analysis of these properties in a large set of seagrass meadows under contrasting conditions of nutrient availability in the Philippines and Thailand. The ramet size differed by two orders of magnitude between the smallest species, Halophila ovalis (12 mg DW per ramet), and the largest, Enhalus acoroides (7.4 g DW per ramet). However, the pattern of mass allocation to different ramet components was similar among species. The vertical rhizome was the most variable ramet component. Compared to seagrasses in general, nitrogen concentrations in the leaves of these South-east Asian seagrasses were low (leaf N ≤ 2% DW), and the phosphorus concentrations high (leaf P > 0.2% DW). The amount of nutrients allocated to leaves was of the same magnitude as that to rhizomes and roots. Seagrass ramet mass and the percentage of mass allocated to roots were independent of total nitrogen or phosphorus in the sediment for most species. The nutrient concentrations of seagrass tissues differed among coexisting species which suggests that differences in the nutritional status among South-east Asian species are more dependent on species-specific differences in nutrient acquisition or requirements than on nutrient availability in the sediment.