The effects of four environmental stressors—Temperature, irradiance, desiccation, and salinity—On the photosynthesis of a cultivated green alga, Gayralia kuroshiensis (Ulvophyceae), from Fukushima, Japan

Cultivated green alga Gayralia kuroshiensis ( Hirohano-hitoegusa , formerly referred to as Monostroma latissimum in Japan) is ecologically and industrially important. However, the effects of key intertidal stressors on its physiology remain poorly understood, particularly with respect to desiccation and salinity. Photosynthetic responses of cultivated thalli to photosynthetically active radiation (PAR), temperature, desiccation, and salinity were quantified using pulse-amplitude modulation (PAM)-chlorophyll fluorometry and oxygenic photosynthesis measurements. No marked photoinhibition was detected even under high irradiance. Net photosynthetic rates ( NP max ) peaked at 24 °C, and saturation irradiance ( E k ) was lower at 6 and 15 °C. The effective quantum yield (Δ F / F m ′) was well maintained at 4–20 °C. In desiccation experiments, Δ F / F m ′ declined when relative water content (RWC) fell below 50%, but recovered to near-initial levels after rehydration when RWC remained above 10%. Δ F / F m ′ also remained stable across a wide range of salinities (5–60 psu). These results suggest that G. kuroshiensis possesses physiological traits adapted to fluctuating intertidal environments and provide fundamental information for optimizing cultivation conditions. • The photosynthetic response of Gayralia kuroshiensis (Ulvophyceae) was examined. • The results revealed its ability to adjust photosynthesis across seasons. • This alga exhibits strong desiccation tolerance and recovery capacity. • This alga exhibits high euryhalinity.