Acid treatment combined with high light leads to increased removal efficiency of Ulva prolifera

Abstract

The attachment of Ulva prolifera to Pyropia rafts can cause severe economic losses during the cultivation of Pyropia because it can reduce the yield, harvest, and quality of the Pyropia. The existing methods for removing U. prolifera from the Pyropia raft have many limitations, such as low removal efficiency, Pyropia damage, and environmental pollution. In this study, we developed method that can effectively remove U. prolifera attached to the raft during Pyropia cultivation. After 3 h of citric acid (pH 4.0) and high light treatment (1200 μmol photons m2− s1−), followed by recovery in seawater for 24 h, the U. prolifera was completely dead, but the Pyropia was still active. We also studied the response mechanism of U. prolifera to acid and high light, and our results showed that under acidic and high light conditions, H+ may penetrate the interior of U. prolifera cells, causing obvious synergistic injury with high light to PSII in U. prolifera. The degradation of Cyt f in this process severely hindered electron transport and slightly reduced PSI activity. Acid also destroyed the U. prolifera photoprotective mechanism, as shown by the high non-photochemical quenching (NPQ) values and xanthophyll cycle pigment contents. This study provides a solid base for further research on optimizing the treatment of U. prolifera and improving its removal efficiency.