ABSTRACT
Microcystis aeruginosa is a common bloom-forming cyanobacterium, which generally coexists and competes with Chlorella pyrenoidosa in lakes. Sonication can be used for emergency management of algal blooms. Ultrasound influences algal growth and physiological parameters, as well as interspecific competition in algal community. To explore the effects of ultrasonic stress (35 kHz, 0.035 W·cm-3) on physiological characteristics and interspecific competition of algae, M. aeruginosa and C. pyrenoidosa were sonicated in mono- and co-cultures (1:1 mixture, according to cell concentration). Results showed that M. aeruginosa was more sensitive to ultrasonic stress. After the sonication for 600 s, both photosynthetic activity (Fv/Fm) and esterase activity of M. aeruginosa showed significant changes, with Fv/Fm values in mono- and co-cultures being decreased by 51.8% and 64.7%, respectively. In comparison, Fv/Fm values of C. pyrenoidosa changed slightly. M. aeruginosa released more chromophoric dissolved organic matter (CDOM, including tryptophan-, tyrosine-, and fulvic-like substances) than C. pyrenoidosa. The cell concentration of C. pyrenoidosa showed little changes regardless of sonication time, while the cell concentration of M. aeruginosa decreased at different degrees. The cell concentration of M. aeruginosa in co-cultures decreased by 42.6% after sonication for 600 s, which might be responsible for the dominance of C. pyrenoidosa during 8 days after sonication. M. aeruginosa inhibited C. pyrenoidosa in other treatments, but mutual inhibition appeared in the 600 s sonication treatment. After ultrasonic treatment, the activity of M. aeruginosa could recover gradually. The treatment should be conducted again within a week to improve the persistence of algal control.
Subject(s)
Chlorella , Cyanobacteria , Microcystis , Microcystis/physiology , Chlorella/physiology , Photosynthesis , LakesABSTRACT
Suspended particulate matter (SPM) and sediments are important sources of dissolved organic matter (DOM) in lake water. However, studies on what extent and how both sources affect DOM composition are lacking, which hampers DOM management. Herein, DOM, SPM-extracted particulate organic matter (POM), and sediment-extracted organic matter (SOM) were characterized and compared in terms of absorption spectral properties and chemical composition in Lake Taihu, a large cyanobacterial bloom-affected shallow lake. A statistical method was proposed to quantify the similarity of organic matter (OM) in the different states and to evaluate the potential effects of SPM and sediments on DOM. Results showed that POM and DOM were mainly composed of small-molecular-size and low-humified organic components (i.e., 27 %-38 % tryptophan-like and ~30 % protein-like substances), and most of them were derived from autochthonous sources. While tyrosine-like (57 %) and humic-like (27 %) substances were dominant in SOM. The OM similarity between POM and DOM was approximately 1.5 times higher than that between SOM and DOM, indicating the greater effect of SPM than sediments on DOM composition. High pH and low nitrogen (e.g., nitrate and ammonia) were positively correlated to the OM similarity between POM and DOM. Further, the findings indicated that nitrogen limitation enhanced the OM exchange between POM and DOM by promoting the production of extracellular polymeric substances (EPS) in cyanobacterial aggregates. The obtained findings highlighted the importance of SPM in shaping the DOM composition relative to sediments and facilitating the DOM management in bloom-affected lakes.
