Contrasting Photophysiological Characteristics of Phytoplankton Assemblages in the Northern South China Sea

• Published in: PloS one Vol. 11; no. 5; p. e0153555
• Main Authors: Jin, Peng, Gao, Guang, Liu, Xin, Li, Futian, Tong, Shanying, Ding, Jiancheng, Zhong, Zhihai, Liu, Nana, Gao, Kunshan
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 19.05.2016; Public Library of Science (PLoS)
• Subjects: Absorption; Absorption cross sections; Acclimation; Acclimatization; Acidification; Biology and Life Sciences; Calibration; Carbon; Carbon budget; China; Chlorophyll; Chlorophyll - physiology; Chlorophyll A; Climate; Darkness; Earth Sciences; Ecology and Environmental Sciences; Efficiency; Electrons; Environmental changes; Environmental conditions; Environmental science; Fluorometers; Fluorometry; Freshwater; Genotype; Geography; Hydrologic cycle; Laboratories; Oceans and Seas; Photochemical Processes; Photochemicals; Photosynthesis; Photosystem; Photosystem II; Photosystem II Protein Complex - physiology; Physical Sciences; Physiological aspects; Physiology; Phytoplankton; Phytoplankton - physiology; Plankton; Productivity; Properties; Regional climates; River plumes; Rivers; Stations; Water depth; China; South China Sea; ISEW, South China Sea
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0153555

The growth of phytoplankton and thus marine primary productivity depend on photophysiological performance of phytoplankton cells that respond to changing environmental conditions. The South China Sea (SCS) is the largest marginal sea of the western Pacific and plays important roles in modulating regional climate and carbon budget. However, little has been documented on photophysiological characteristics of phytoplankton in the SCS. For the first time, we investigated photophysiological characteristics of phytoplankton assemblages in the northern South China Sea (NSCS) using a real-time in-situ active chlorophyll a fluorometry, covering 4.0 × 105 km2. The functional absorption cross section of photosystem II (PSII) in darkness (σPSII) or under ambient light (σPSII') (A2 quanta-1) increased from the surface to deeper waters at all the stations during the survey period (29 July to 23 August 2012). While the maximum (Fv/Fm, measured in darkness) or effective (Fq'/Fm', measured under ambient light) photochemical efficiency of PSII appeared to increase with increasing depth at most stations, it showed inverse relationship with depth in river plume areas. The functional absorption cross section of PSII changes could be attributed to light-adapted genotypic feature due to niche-partition and the alteration of photochemical efficiency of PSII could be attributed to photo-acclimation. The chlorophyll a fluorometry can be taken as an analog to estimate primary productivity, since areas of higher photochemical efficiency of PSII coincided with those of higher primary productivity reported previously in the NSCS.