Effects of Nitrogen and Phosphorus in Sediment on the Occurrence of <i>Cladophora</i> sp. (Cladophoraceae) in Aquaculture Ponds

To explore the impact of sedimentary nitrogen and phosphorus on <i>Cladophora</i> occurrence, we conducted a microecosystem experiment simulating different nitrogen and phosphorus content as well as nitrogen-to-phosphorus ratios in the sediment. Subsequently, to further explore the specific mechanism of influence that epiphytic algae have on <i>Cladophora</i>, we designed various microsystem culture experiments. These results revealed that an N/P ratio of 40:1 was relatively unfavorable for <i>Cladophora</i> growth. Additionally, there was an extremely significant negative correlation between the benthic cyanobacteria coverage on the sediment surface and the wet weight of <i>Cladophora</i> (<i>p</i> < 0.01), indicating that benthic cyanobacteria could inhibit the growth of <i>Cladophora</i>. Total nitrogen levels in the water column showed a significant positive correlation with phytoplankton biomass (<i>p</i> < 0.05), while benthic cyanobacteria coverage exhibited an extremely significant positive correlation with phytoplankton biomass through phosphorus absorption and nitrogen release (<i>p</i> < 0.01). Metabolite analysis of benthic cyanobacteria identified annotations for 313 metabolites; among them cis,cis-muconic acid (32.48‰), erucamide (9.52‰), phosphoric acid (6.97‰), fenpropidin (6.53‰), and propionic acid (5.16‰) accounted for proportions exceeding 5‰. However, none of these metabolites have been recognized as allelochemicals or toxins at present. This study provides novel insights into controlling <i>Cladophora</i> occurrence by considering sediment nutrients, including nitrogen and phosphorus, along with allelochemicals.