Iris Ann Borlongan

Light and temperature effects on photosynthetic activity of E ucheuma denticulatum and K appaphycus alvarezii (brown and green color morphotypes) from Sulawesi Utara, Indonesia

Knowledge concerning the effects of several abiotic factors on the physiology of carrageenophytes is essential both in ecological and economic standpoints, to ensure their sufficient supply for the sustainability of seaweed‐based industries. This paper presents the photosynthetic characteristics of farmed carrageenophytes, E ucheuma denticulatum and K appaphycus alvarezii [brown (BRN) and green (GRN) color morphotypes] from Sulawesi Utara (Sulawesi Island), Indonesia, as determined by examining their photosynthetic response across different temperatures and irradiances using dissolved oxygen measurements and pulse‐amplitude modulated fluorometer. Net photosynthesis–irradiance ( P – E ) curves at 26°C revealed that net photosynthetic rates of the three seaweeds gradually increased until the estimated saturation irradiances ( E k ) of 58 μmol photons m− 2 s−1 (49–68 μmol photons m− 2 s−1, 95% Bayesian prediction intervals; BPI) for E . denticulatum, and 158 and 143 μmol photons m− 2 s−1 (134–185 and 99–203 μmol photons m− 2 s−1, 95% BPI) for BRN and GRN K . alvarezii, respectively; and that no photoinhibition was observed at the highest irradiance of 1000 μmol photons m− 2 s−1. All seaweed samples exhibited photosynthetic tolerance to high PAR as shown by their recovery in maximum quantum yields (Fv / Fm ) following chronic exposures; as well as tolerance over a broad range of temperature, which is from 19 to 33°C for E . denticulatum, 20–29°C for BRN K . alvarezii, and 17–32°C for GRN K . alvarezii. Temperature responses of these carrageenophytes indicated that they were well‐adapted to the annual seawater temperatures in the cultivation site; however, they are also likely close to threshold levels for thermal inhibition, given the decline in Fv / Fm above 30°C.

Effects of temperature and PAR on the photosynthesis of Kappaphycus sp. (Solieriaceae, Rhodophyta) from Okinawa, Japan, at the northern limit of native Kappaphycus distribution in the western Pacific

Abstract: The successful cultivation of the Japanese Kappaphycus sp. (K. striatus auctorum japonicorum) in Okinawa, Japan, requires the detailed understanding of its physiological response to environmental factors. The photosynthetic performance of this native red alga was investigated under a variety of temperature and photosynthetic active radiation (PAR) conditions by employing methods based on pulse amplitude modulation–chlorophyll fluorometry and dissolved oxygen sensors. The net photosynthesis–irradiance (P–E) curve at 24°C revealed that the compensation (Ec) and saturation (Ek) irradiances were 26 [95% Bayesian prediction interval (BPI), 11–29 μmol photons m−2 s−1] and 140 (95% BPI, 98–192) μmol photons m−2 s−1, respectively. No inhibition in oxygenic evolution and quantum yield was observed at the highest PAR of 1000 μmol photons m−2 s−1. However, the ability of the seaweed to recover from photoinhibition was complicated following long-term PAR exposures at 18°C but not at 28°C. The Japanese Kappaphycus sp. showed photosynthetic optima at 17.4–29.1°C, derived from the Fv/Fm and gross photosynthesis–temperature models, respectively. These characteristic results were closely related to the depth of its habitat and its northern limit of distribution in Okinawa as influenced primarily by seawater temperature. Findings of this study should be useful to the development of culture systems adapted for subtropical waters, whether for commercial purpose or for conservation of natural communities.

Photosynthetic activity of two life history stages of Costaria costata (Laminariales, Phaeophyceae) in response to PAR and temperature gradient

Abstract: Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were investigated in the macroscopic sporophyte (SPO) and microscopic gametophyte (GAM) stages of the brown alga Costaria costata from Hokkaido, Japan. Measurements of net photosynthesis, respiration rates and photochemical efficiency were carried out using dissolved oxygen sensors and a pulse amplitude–modulated fluorometer. Net photosynthesis–irradiance curves of the two life history stages revealed a similarity in their light-saturated photosynthesis rates but a difference in initial slopes, with lower efficiency in oxygenic evolution for SPO than for GAM. Consequently, compensation PAR (Ec = 9 μmol photons m−2 s−1) and saturation PAR (Ek = 243 μmol photons m−2 s−1) of the sporophyte were higher than for the gametophyte (Ec = 1 μmol photons m−2 s−1; Ek = 44 μmol photons m−2 s−1). This reflects the low-PAR adaptation of the microscope stage that is commonly found on the underside of rocks or in crevices where light exposure is limited. Continuous exposures to low (6 h, 100 μmol photons m−2 s−1) and high PAR (1000 μmol photons m−2 s−1) induced photoinhibition of photosynthesis, with larger declines in gametophyte effective quantum yields (ΦPSII). Gametophyte maximum quantum yields (Fv/Fm) also did not fully recover even after 12 h of dark acclimation, indicating photodamage. As for the temperature response in C. costata, gross photosynthesis and Fv/Fm characteristics were similar for both developmental stages, with temperature optima ranging from 14°C to 22°C. Their Fv/Fm and oxygenic net photosynthesis were relatively insensitive to low temperatures but declined above 24°C. This may explain the disappearance of C. costata sporophytes from their habitat during summer as well as their southern distributional limit in the western Pacific.

Photosynthetic responses to photosynthetically active radiation and temperature including chilling-light stress on the heteromorphic life history stages of a brown alga, Cladosiphon okamuranus (Chordariaceae) from Ryukyu Islands, Japan: Photosynthesis of Cladosiphon okamuranus

Photosynthetic responses to temperature and photosynthetically active radiation (PAR) were investigated on the heteromorphic life history stages (macroscopic and microscopic stages) of an edible Japanese brown alga, Cladosiphon okamuranus from the Ryukyu Islands. Measurements were carried out by using optical dissolved oxygen sensors and a pulse‐amplitude modulated fluorometer. Maximum net photosynthetic rates and other parameters of the Photosynthesis – PAR curves at 28°C were somewhat similar in both life history stages, without characteristic photoinhibition at 1000 μmol photons m−2 s−1. Results of oxygenic gross photosynthesis and dark respiration experiments over a temperature range of 8–40°C revealed similar temperature optima for both stages (29.7°C, macroscopic stage; 30.3°C, microscopic stage), which support their observed occurrences in the habitat during summer. Maximum quantum yields of photosystem II (PSII) (F v/F m) were relatively stable at low temperatures with the highest at 15.1°C for the macroscopic stage and at 16.5°C for the microscopic stage; but dropped at higher temperatures especially above 28°C. Continuous exposures (6 h) to 200 and 1000 μmol photons m−2 s−1 at 8, 16, and 28°C revealed greater depressions in effective quantum yields of PSII (Φ PSII) of the microscopic stage at 8°C, as well as its F v/F m that barely increased after 6 h of dark acclimation. Whereas post‐dark acclimation F v/F m of both stages exposed to low PAR fairly recovered at 28°C, suggesting their photosynthetic tolerance to such high temperature. Under natural conditions, both heteromorphic stages of C. okamuranus may persist throughout the year in this region. Beyond its northern limit of distribution, the microscopic stage of this species may suffer from photodamage, as enhanced by low winter temperatures; hence, its restricted occurrence.

Assessment of photosynthetic performance in the two life history stages of Alaria crassifolia (Laminariales, Phaeophyceae): Photosynthesis of Alaria crassifolia

Understanding of the physiological responses of kelp to environmental parameters is crucial, especially in the context of environmental change that may have contributed to the decline of kelp forests all over the world. The current study presents the photosynthetic characteristics of the macroscopic sporophyte and microscopic gametophyte stages of the brown alga Alaria crassifolia from Hokkaido, Japan, as determined by examining their photosynthetic responses over a range of temperature and irradiance using dissolved oxygen and chlorophyll fluorescence measurements. Net photosynthetic rates of the sporophyte were consistently higher than those of gametophyte across temperature gradients and irradiance levels. Photosynthesis–irradiance curves at 8°C, 16°C, and 20°C revealed similar initial slopes (α = 0.4–0.9) on the two life history stages, but higher compensation (E c = 4–7 μmol photons m−2 s−1) and saturation irradiances (E k = 53–103 μmol photons m−2 s−1) for the sporophyte than for the gametophyte (E c = 0–7 μmol photons m−2 s−1; E k = 7–10 μmol photons m−2 s−1). Both stages exhibited chronic photoinhibition, as shown by the failure of recovery in their maximum quantum yields (F v/F m) following high irradiance stress, with greater possibility of photodamage at low temperature. Gametophytes were less sensitive to low temperatures than sporophytes, given their relatively stable F v/F m response. Nevertheless, temperature optima for photosynthesis of both stages coincide with each other at 20–23°C, which correspond to the growth and maturation periods of A. crassifolia in Japan. This species is also likely to suffer from thermal inhibition as both GP rates and F v/F m decreased above 24°C.