Research On Limiting Effect Of Nutrients To Phytoplankton Growth And Simultaneous Carbon Cycling

Phytoplankton growth is the key factor controlling the concentration of nutrient and carbon cycling in the surface sea water. The limiting effect of nutrient to phytoplankton growth has been an important research field in marine ecology. When phytoplankton grows carbon element will be transported in different supporter such as sea water and particulate matter (PM). At the same time the form which carbon presence will changed among dissolved inorganic carbon(DIC), dissolved organic carbon(DOC) and particulate organic carbon(POC).So it is significative to study the carbon element record and the character of stable carbon isotope for carbon cycling research in surface sea water even the whole world.The nutrient enrichment experiments were carried out in Pacific, Atlantic, Indian ocean and South China Sea(SCS).Comparing the concentration of nutrient and Chl-a in the incubating water we know the limiting nutrient in different sea area. In Pacific N is the most important limiting nutrient, the effect of P to phytoplankton growth is not obvious, and Si adding has little influence. In Atlantic the limiting effect of these three kinds of nutrient is similar to that in Pacific. In Indian Ocean the co-limiting of N and P has most obvious effect to phytoplankton growth. In SCS N and P co-limit the growth of phytoplankton growth. The variety of temperature, concentration of Chl-a and phytoplankton grow rate(R) show that the community has small sensitivity to temperature. In addition, the ratio of N to P in sea water cann't dominates the limiting nutrient in it.During the second experiment in Indian Ocean the concentration of DIC, DOC and POC were analyzed. At the same time theδ¹³C value were investigated. These parameters provide evidences for carbon cycling as phytoplankton grows.The concentration of DIC is not sensitive to the variety of temperature and phytoplankton blooming. It shows that photosynthesis and temperature are not major factors influencing the concentration of DIC. In the course of phytoplankton bloom the DIC in sea water will be utilized and represented as DOC which will result in the increase of the concentration of POC. At the same time the phytoplankton exudation will increase the concentration of DOC in sea water. Under the action of bacteria died phytoplankton will be decomposed which will increase the concentration of DIC and DOC. The increased DOC whether produced by phytoplankton exudation or its decomposition will benefit the growth of bacteria and increase the concentration of POC. The data of biochemical composition in PM shows that PM is mainly composed by plankton. Lipid is the most important biochemical composition and the content of amino acid and carbohydrate in PM is smaller.Analyzing the value ofδ¹³C_DIC,δ¹³C_DOC,R and the concentration of Chl-a we suggest that the effect of phytoplankton bloom to carbon isotope fractionation is not obvious. Theδ¹³C_DIC value become much lighter after phytoplankton bloom which was resulted from the remineralization of PM. The character ofδ¹³C_POC is mainly in touch with bacteria growth. In addition, the average value ofδ¹³C_{è„‚è´¨} is smaller than that ofδ¹³C_{氨基酸} andδ¹³C_{ç³–ç±»} and it keeps steady in the course of experiment. Theδ¹³C value of these biochemical compositions and their concentration have close relationship with theδ¹³C_POC value.