Effects of water depth on clonal characteristics and biomass allocation of Halophila ovalis (Hydrocharitaceae)

Halophila ovalis is a dioecious seagrass with a wide geographical and water depth range.The objective of this study was to understand its plasticity in clonal characteristics and biomass and also its allocation between above-and belowground in seagrass beds at different water depths.Methods Four monospecific H.ovalis beds,Shabei,Xialongwei,Beimu and Yingluo,which have different water depths at maximum tide level(MTL)but otherwise similar environmental conditions,were studied.We measured main clonal characteristics,i.e.horizontal internodal length,branching angle,shoot height,leaf length and width,and rhizome diameter.Above-and belowground biomasses of H.ovalis were also estimated using a harvest method.Important Findings We found no significant differences in coverage,leaf pair density or number of stem nodes per square meter between the four study sites.However,horizontal internodal length,leaf length,width,rhizome diameter and shoot height all increased significantly with the increases in water depth from 2-to 9-m MTL and decreased when the water depths were greater than 9-m MTL.No significant difference in above-or belowground biomass between the seagrass beds was found.However,the ratio of above-to belowground biomass was significantly higher in the shallowest site compared to the other three seagrass beds,indicating that more biomass was stored belowground in deeper water.The results demonstrated plastic responses in clonal characteristics and biomass allocation in H.ovalis across the water depth gradient.

Isolation and Characterization of Phosphate-Solubilizing Bacteria from Seagrass Rhizosphere Soil

Phosphate-solubilizing bacterial strains(6 Nos.) were isolated from the rhizosphere soils of two seagrasses(Halophila ovalis(R.Br.) Hook and Halodule pinifolia(Miki) Hartog) in the Vellar estuary.Experimental studies found that the strain PSSG6 was effective in phosphate solubilization with Phosphate Solubilization efficiency index E = 375 ± 8.54,followed by the strain PSSG5 with Phosphate Solubilization efficiency index E = 275 ± 27.3.Of the 6 strains isolated,the strains PSSG4 and PSSG5 be-longed to the genus Bacillus,and PSSG1,PSSG2 and PSSG3 were identified as Citrobacter sp.,Shigella sp.,and Klebsiella sp.,respectively,by conventional method,and PSSG6 was identified as Bacillus circulans using conventional and molecular methods.