The interactive effects of elevated temperature and nutrient concentrations on the physiological responses of Ulva linza Linnaeus (Ulvales, Chlorophyta)

Abstract

We tested the interactive effects of increased temperature and nutrient (ammonium, NH4+) levels on physiological properties such as photosynthetic rates, NH4+ uptake rates, relative growth rates, chlorophyll fluorescence, and tissue nutrient contents in Ulva linza Linnaeus. The experiments were conducted at four temperatures (LT, low temperature (15 °C); MT, medium temperature (20 °C); CT, control temperature (25 °C); and HT, high temperature (30 °C)) and three NH4+ concentrations (LN, low nutrient (4 μM); MN, medium nutrient (60 μM); and HN, high nutrient (120 μM)). The interaction between temperature and NH4+ levels influenced the photosynthetic rates, NH4+ uptake rates, relative growth rates, photosynthetic efficiency, tissue nitrogen contents, and C:N ratios in algal tissues. Temperature strongly affected the photosynthetic rates, NH4+ uptake rates, and photosynthetic efficiency. Nutrient enrichment increased the photosynthetic rates, nutrient uptake rates, relative growth rates, photosynthetic efficiency, tissue nitrogen contents, and tissue C:N ratios. Our study results could help understand the physiological responses of U. linza under future ocean environmental conditions such as ocean warming and eutrophication.