Response of periphyton fatty acids to experimental changes in aqueous phosphorus

Periphyton is an important basal food source for many aquatic consumers by directly or indirectly providing long-chain polyunsaturated fatty acids (LC-PUFA). Although periphyton LC-PUFA content is highly sensitive to aqueous nutrients, the majority of prior studies have been conducted in low-nutrient aquatic environments. Less is known about how periphyton LC-PUFA content may change in response to higher nutrient concentrations in rivers. We conducted a periphyton culturing experiment by manipulating a gradient of aqueous nutrient concentrations from 0.002 to 0.18 mg P/L to investigate how aqueous nutrients affected periphyton FA from oligotrophic to eutrophic waters. Our results showed a significant curvilinear relationship between aqueous water nutrients and periphyton FA. In oligotrophic conditions, periphyton LC-PUFA increased as aqueous nutrients increased, whereas in eutrophic waters, periphyton LC-PUFA decreased as aqueous nutrients increased. The change of taxonomic composition, especially the increase of diatom density, was a significant factor influencing periphyton LC-PUFA content. Additionally, periphyton biomass experienced a significant increase with elevated aqueous nutrients, which differed from periphyton LC-PUFA. Our study detected the response of periphyton FA to aqueous nutrients from oligotrophic to eutrophic conditions, and provided a reference for the protection of river ecosystems.