title: A comparative study of the photosynthetic capacity in two green tide macroalgae using chlorophyll fluorescence.
abstract: Green tides have occurred in the Yellow Sea, China, every year from 2007 to 2015. The free-floating Ulva prolifera (Müller) J. Agardh was the causative macroalgal species. The co-occurring, attached U. intestinalis was also observed. Photosynthetic capacities were determined using chlorophyll fluorescence in situ and after 7 days lab acclimation, and a significant differences were noted. Pigment composition showed no obvious differences, but concentrations varied significantly, especially chlorophyll b in U. prolifera two times increase was observed after acclimation. The optimal photochemical efficiency of PS II (Fv/Fm) was significantly higher in U. prolifera. Photosynthetic rate (α), maximum relative electron transport rate (rETRmax), and minimum saturating irradiance (Ek), obtained from rapid light response curves (RLCs), showed almost the same photosynthetic physiological status as Fv/Fm. Quenching coefficients and low temperature (77 K) chlorophyll fluorescence emission spectra of thylakoid membranes analysis showed U. prolifera has a better recovery activity and plasticity of PSII than U. intestinalis. Furthermore, energy dissipation via non-photochemical quenching (NPQ) and state transitions showed efficacious photoprotection solution especially in U. prolifera suffered from the severe stresses. Results in the present study suggested that U. prolifera's higher photosynthetic capacity would contribute to its free-floating proliferation, and efficacious photoprotection in addition to favorable oceanographic conditions and high nutrient levels support its growth and aggregation.
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Tongfei
authors.initials: T
authors.lastname: Qu
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Xianghai
authors.initials: X
authors.lastname: Tang
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Hui
authors.initials: H
authors.lastname: Xiao
authors.affiliation: Department of Marine Ecology, College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
authors.forename: Xuexi
authors.initials: X
authors.lastname: Tang
keywords: 77 K chlorophyll fluorescence; Chlorophyll fluorescence; Optimal photochemical efficiency; Quenching coefficient; Yellow sea green tide