Study On Photosynthesis Of Seagrass Zostera Japonica In Fangcheng Of Guangxi

Seagrass are higher-level plants lived in the intertidal and subtidalzone, and they are a small but diverse group of mostly submersed marineangiosperms, which inhabit environments that characterized by periodiclight limitation and high salinity. Seagrass bed is one of the majornearshore habit types and plays a important role in marine ecosystems.The high productivity of seagrass beds places them among the mostproduction of all marine ecosystems. But the global change and humanactivity have led to the large scale loss of seagrass. For protection andrecovery of seagrass, we should study their photosynthetic ecophysiology.The objective of this study aims to reveal the photosynthesis of Zosterajaponica effected by factors such as light, temperature, inorganic carbon,salinity and water stress. This study combines the laboratory and the fieldexperiment to analyze the relationship between the photosynthesis ofZosterajaponica and environment factors. The net photosynthetic rate and respirating rate generally increasedin response to increasing temperature for photosynthesis within the range15-30℃and the observed trends suggested the optimum temperaturerange for photosynthesis was between 25-30℃, below the 20℃thephotosynthetic rate dropped sharply. Also with the increasing lightintensity the net photosynthetic rate increased and the optimum lightintensity is about 200001x. The compensation light intensity range wasbetween 100-4001x. According to examine the vertical distribution oflight intensities in the field, we estimated that Zosterajaponica was ableto live in the area with the water depth of 4m.The effects of pH changes on photosynthesis in Zostera japonicawere examined under laboratory condition. It showed a general increasein photosynthetic rate with pH, and obtained the peak photosynthetic rateat 7 and maintaining high photosynthetic rate up to 9. In addition, thephotosynthesis related with the increasing HCO₃^-concentration of water.The results showed that Zostera japonica mainly use HCO₃^- as theinorganic carbon source.Intertidal seagrass usually experiences periodical exposures to air atlow tide, which is the greatest environmental stress. Zostera japonicaexhibited a linear decline in Fv/Fm when the water loss exceeded 50%.Below the 50% water loss, this trend was not significant. The resultsindicated the Zostera japonica had a tolerance to slight water loss, but excessive water loss would lead to death.Zostera japonica was able to tolerate high salinity up to 45 psu, andtheir optimum salinity was between 25-35 psu. It obtained a higherphotosynthetic rate in high salinity than in low salinity and showed a lowsalinity threshold(0-10 psu). Its toleratce to high salinity associated withthe relatively high salinity condition.Zostera japonica had relative high photosynthetic rate in spring andautumn, but had lowest photosynthetic rate in summer. This seasonalchange depended on the interaction of light, temperature and tide.In conclusion, Zostera japonica was a species of great tolerace.Light availability and limited inorganic carbon source may havecontributed to the varivation of photosynthesis. Due to the significantinfluence of tide in light availability resulting in light restrictions andexposures to air at low tide for seagrass, tide should be take into accountwhen manageing coastal waters with the aim of allowing for thesuccessful growth of seagrass.