The Dynamics In Biomass And Caloric Value In Zostera Japonica Seagrass

Seagrass bed is one kind of the representative marine ecosystems like mangrove, coral reefs and so on. Being a category of Monocotyledons in the shallow water, they are adapted well to the marine habitats. My research was designed to study: (1) the year-round dynamics in the biomass and caloric value of Zostera japonica seagrass meadow in Zhenzhu Bay, Fangchenggang city, Guangxi province; (2) The caloric values of Zostera japonica in the different development stages; And (3) comparison of the caloric values in four species of seagrass in Southern China. The goal of this study was to provide with scientific data for the protection, restoration and sustainable utilization of seagrass in China.The results are as follow:1. The average year-round biomass of aboveground organs in Zostera japonica was 21.97 g.DW.m^-2, and that in the underground organs was 24.53 g. DW. m^-2. It seemed that the biomass changed evenly through the whole year, it was however higher in April and lower in August. The ratios of the aboveground biomass to the underground were higher than 1 in March, April, July and August, while those were lower than 1 in other months. The biomass of Zostera japonica increased significantly with the increasing distance off the shore.2. In the aboveground part of Zostera japonica, the average year-round gross caloric value was 13.43kJ/g, the average ash free caloric value 16.22 kJ/g and the average ash content 17.03%. And in the underground part, the average year-round gross caloric value was 12.33 kJ/g, the average ash free caloric value 15.76 kJ/g and the average ash content 21.72%.3. The gross caloric values in Zostera japonica and Cymodocea rotundata (two species in family Potamogetonaceae) were higher than those in Enhalus acoroides and Thalassia hemperichii (two species in family Hydrocharitaceae). The ash contents varied among these four species, with the lowest recorded in Zostera japonica. The decreasing order in the ash-free caloric values was Cymodocea rotundata, Thalassia hemperichii, Zostera japonica and Enhalus acoroides.4. The gross caloric values in mature leaf and stem were higher than those in young leaf and stem in Zostera japonica. Along with the aging process, the ash content in leaf increased, while those in stem decreased. The maximum of ash free caloric value occurred in the mature leaf, 16.57kJ/g, and the minimum in old stem, 14.19kJ/g.5. The N/P ratios in leaf of Zostera japonica were 16 in autumn and winter, 10.2 in spring. The N/P ratios in stem were highest in autumn, 11.8, and lowest in spring, 4.9. In contrast to other plants, the contents of N and P in these four species of seagrass were higher. The N contents in leaves were always higher than those in stems, but the P contents did not obey the same rule as the N contents. Both the N and P contents increased along with the aging process.