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.

Keywords: 77 K chlorophyll fluorescence; Chlorophyll fluorescence; Optimal photochemical efficiency; Quenching coefficient; Yellow sea green tide.

Fig. 1

Mean optimal photochemical efficiency of photosynthesis (Fv/Fm) of U. prolifera and U. intestinalis, obtained from in situ and 7 days’ acclimation to each. Values are mean ± SD (n = 5). Different letters above bars indicate significantly different values (post hoc, p < 0.05)

Fig. 2

Mean relative electron transport rate (rETR) and fitted rapid light response curves (RLCs) of U. prolifera and U. intestinalis, obtained from in situ and 7 days’ acclimation to each. Values are mean ± SD (n = 5)

Fig. 3

Mean maximum relative electron transport rate (rETRmax) obtained from fitted rapid light response curves (RLCs) of U. prolifera and U. intestinalis, measured in situ and 7 days’ acclimation to each. Values are mean ± SD (n = 5). Different letters above bars indicate significantly different values (post hoc, p < 0.05)

Fig. 4

Mean photosynthetic rate in light-limited region of RLC (α) obtained from fitted rapid light response curves (RLCs) of U. prolifera and U. intestinalis, measured in situ and 7 days’ acclimation culture to each. Values are mean ± SD (n = 5). Different letters above bars indicate significantly different values (post hoc, p < 0.05)

Fig. 5

Mean minimum saturating irradiance Ek obtained from fitted rapid light response curves (RLCs) of U. prolifera and U. intestinalis, measured in situ and 7 days’ acclimation to each. Values are mean ± SD (n = 5). Different letters above bars indicate significantly different values (post hoc, p < 0.05)

Fig. 6

Quenching coefficient photochemical quenching (qP) as a function of increasing irradiances, obtained from in situ and 7 days’ acclimation culture to each. Values are mean ± SD (n = 5)

Fig. 7

Quenching coefficient non-photochemical quenching (NPQ) a function of increasing irradiances, obtained from in situ and 7 days’ acclimation culture to each. Values are mean ± SD (n = 5)

Fig. 8

77 K chlorophyll fluorescence emission spectra of thylakoid membranes obtained from in situ and 7 days’ acclimation culture to each. Each curve was the mean of five independent experiments. The excitation wavelength was 436 nm