Comparison of nutrient uptake characteristics and osmotic adjustment of two co-occurring morphotypes, Ulva prolifera and Ulva linza, in a range of concentrations of seawater

Abstract

The purpose of this study was to investigate the nutrient uptake characteristics, osmotic adjustment abilities, and photosynthetic efficiency of floating-type U. prolifera (UP-FL), fixed-type U. prolifera (UP-FIX), and U. linza (UL) under varying salinity conditions. Our results demonstrated that UP-FL exhibited the broadest salinity tolerance, with significantly higher relative growth rates (RGR), photosynthetic efficiency, and osmotic adjustment ability (OAA) compared to UP-FIX and UL. The increased concentrations of potassium ions (K⁺) and proline (PRO) in UP-FL under high salinity were identified as key factors contributing to its superior salt tolerance. In contrast, U. linza showed lower RGR, photosynthetic efficiency, and OAA, indicating reduced adaptability to high salinity environments. The study also revealed that both UP-FL and UL respond to salinity stress by accumulating organic solutes such as soluble sugars (SS) and free amino acids (FAAs), which are crucial for osmotic adjustment. These findings highlight the potential of UP-FL for sustainable cultivation in diverse marine environments. Future research should focus on applying these physiological insights to optimize U. linza cultivation strategies, thereby enhancing yield and quality in commercial settings.