Light absorption and impacts of low salinities on photosynthetic behaviour in the epiphytic alga Neosiphonia savatieri (Rhodomelaceae, Rhodophyta)

Abstract

Filamentous epiphyte outbreaks, a serious problem in the commercial cultivation of Kappaphycus/Eucheuma, are often triggered by large changes in abiotic factors. However, the physiological characteristics of epiphytes are poorly understood. In this study, the main pigment contents of Neosiphonia savatieri and its healthy host strains, including green thalli of Kappaphycus striatum (G-KS), brown and green thalli of Kappaphycus alvarezii (B-KA, G-KA), were quantified. The light absorption capacities of lipid- and water-soluble pigments of these seaweeds were also measured. Photosynthetic parameters, including pigment content and fast chlorophyll a fluorescence kinetics, were further studied in N. savatieri exposed to different salinities (16–34 psu) for 10 h in an outdoor experiment. The phycobiliprotein (PBP), Chl-a, and carotenoid contents of N. savatieri were comparatively higher than the hosts, with the values of 2.50, 0.29, and 0.12 mg g−1 (fw), respectively. The mean extinction coefficients of lipid- and water-soluble pigments in N. savatieri were both higher than G-KS, B-KA, and G-KA in the 400–700 nm bands. Salinity of 28 psu increased the pigment contents of the epiphyte, and 16–22 psu did not have a negative impact. Polyphasic fluorescence transients revealed that salinities at 22–28 psu were beneficial to photosynthetic electron transport, mainly attributed to the enhancement of energy absorption per active PSII reaction centre. Given these observations, N. savatieri has a higher light-harvesting capacity and better tolerance to low salinities. These two physiological properties made N. savatieri well suited to the low light and hypo-saline conditions that are frequently triggered by fluctuations in abiotic factors.