Influence Of Nitrogen Nutrients And Iron To The Growth Of Phytoplankton In Mesocosm Experiments

Nitrogen is one of the key elements that control the structure, function, compositions and bio-diversities of marine ecosystem. Iron is the key element which plays important role in the process of chlorophyl bio-synthesizing and nutrition absorbing. Phosphate, silicate, iron or nitrate can be limiting factor in the process of phytoplankton growing. In this essay method of controlled eco-system is used, mesocosm experiment in which iron and different species of nitrogen added in different bags were carried out in the Yellow Sea and South China Sea, the affection of DIN and DON to marine ecosystem is discussed. The results are as follows.1. Phytoplankton specific growth rate:NO₃-N,NH₄-N and CO(NH₂)₂ have promotions on phytoplankton growth,and the promtions were different in different sea area.2. Chlorophyll a size froction:In March 2005 Yeollow Sea cruise,mesocosm experiment showed that microphytoplankton and nanophytoplankton were dominant species in the phytoplankton growing process while in May picophytoplankton seemed to be dominant. In May 2005 South China Sea cruise, mesocosm experiment showed that obvious species substitution occured in the strcture of phytoplankton. This phenomenon could be explained by different respond time of phytoplankton from different areas, nutrients adding changed size-fractionated structure of phytoplankton in a certain extent.3.The affection of nutrients on phytoplankton growth:(1)When concentrate of nutrient comes to a certain degree, nutrients adding has little promotions on phytoplankton growth;(2)The absorbing sequence of phytoplankton to nutrients is CO(NH₂)₂ ,NH₄-N>NO₃-N>NO₂-N; (3)The promotions to diatom varies according to difference species of nitrogen: Nitrate has greate promotion while NH4-N and CO(NH₂)₂ have less; (4)The N/P ratio of phytoplankton...