Ecophysiological Responses Of Phytoplankton To Phosphorus In The Typical Region Of The Yellow Sea

Using bulk and single-cell alkaline phosphatase activity(APA) assay, phosphorus stress and ecophysiological responses of phytoplankton to phosphorus were studied in the typical waters of Yellow Sea during 2006 and 2007.At meantime, the physiological responses of two typical diatoms Skeletonema marinoi and Chaetoceros curvisetus in the Yellow Sea under low phosphorous concentration were also studied in batch culture.The main results were as following:1.APA was measured during two cruises in the Yellow Sea Cold Water Mass (YSCWM) in April and October in 2006,respectively.Phosphorus stress was declined during the cruise in April,2006,which was due to not significant stratifications of YSCWM,however,the stress was serious during the cruise in October,2006,which was becaue of significant stratifications of YSCWM,and thus prevent vertical mixing.On the spatial scale,there was the significant phosphorus stress of phytoplankton in the region between 34°N and 35°N in April,2006, while around 34°N and at the offshore waters ofsoutheasten Yellow Sea.2.For the temporal variations of phytoplankton phosphorus stress in the transects S1 and S3,during the four cruises in April and October,2006,March and August,2007, in the Yellow Sea,phytoplankton community suffered the severest phosphorus stress in August,2007,while the mildest in March,2007.Single-cell APA indicated that phytoplankton species suffered the severest phosphorus stress in August,2007,while the mildest in April,2006.For the comparison of phosphorus stress between diatoms and dinoflagellats,the latter was higher than the former.The characteristics of the specific species and their nutrient strategies might lead the different variations between community and individual cells when they suffered phosphorus stresses. Seasonal variability of YSCWM might also lead the variations of nutrient availablility(e.g.phosphorus) and phosphorus stress of phytoplankton. 3.Skeletonema and Thalassiosira were the dominant genera in the bloom waters, while Chaetoceros and Thalassiosira were the dominant genera in the non-bloom aera in the Yellow Sea in April,2007.Low percentage of labeling species was observed for dominant species.Bulk APA was lower in April,2007 than that in April, 2006.The results also showed that phosphorus stress ofphytoplankton at the middle and bottom of euphoric layer occured earlier than that at the surface.The stress became more and more serious with development of algal bloom.4.Both test species S.marinoi and C.curvisetus could utilize the different phosphorus pools from ambient under phosphorus stress.S.marinoi preferred to utilize soluble reactive phosphorus(SRP) while C.curvisetus liked to utilize internal phosphorus in cells.Due to different abilities and strategies of utilizing soluble reactive/nonreactive phosphorus(SNP),S.marinoi might be the more advantaged competitor in SRP-rich condition while C.curvisetus might be the more advantaged competitor in SRP-poor and SNP-rich condition.