Jutao Liu’s research while affiliated with Jiangxi Academy of Sciences and other places

The frequent occurrence of cyanobacterial blooms poses severe threats to the global environment and to local human health. Therefore, it is vital to develop effective methods to control blooms. Phalaris arundinacea, a dominant hygrophyte in the Lake Poyang wetland, decomposes when submerged during high-water-level periods. Through indoor cultivation experiments, we examined the effects of crude aqueous, ethyl acetate, dichloromethane and petroleum ether extracts of P. arundinacea on the growth of typical harmful bloom-forming cyanobacteria (Microcystis aeruginosa and Dolichospermum flos-aquae). The results revealed that the crude aqueous extract of P. arundinacea significantly inhibited the growth of M. aeruginosa and D. flos-aquae, with average inhibition rates of 86.77 per cent and 80.08 per cent, respectively. The inhibitory effect generally increased with time and dose, with maximum inhibition rates of 99.15 per cent for M. aeruginosa and 97.27 per cent for D. flos-aquae. P. arundinacea crude extracts obtained with ethyl acetate, dichloromethane and petroleum ether reduced the cell density and chlorophyll a concentration of M. aeruginosa. Among the extracts, the petroleum ether extract had the strongest inhibitory effect. Generally, the inhibition rates of these three crude organic solvent extracts peaked on Day 8 or Day 12 of the experiment. The results confirmed that P. arundinacea, a dominant hygrophyte in Lake Poyang, has significant potential for controlling harmful cyanobacterial blooms through the release of allelochemicals and likely plays an important role in this process in summer. Therefore, this study offers novel insights and materials for the prevention and management of cyanobacterial blooms in the future.

Biodegradable plastics, as alternatives to conventional waste plastics, are increasingly applied across various fields. However, the ecological risks associated with the widespread use of biodegradable plastics remain unclear. Additionally, biodegradable plastics tend to age in the environment, leading to changes in their physicochemical properties. The ecological risks brought by the aging of microplastics have also been scarcely studied. In this study, we selected conventional microplastics (PE-MPs), biodegradable microplastics (PLA-MPs), and aged biodegradable microplastics (aging-PLA-MPs) to explore their effects on the rhizosphere soil environment of rice. The results showed that microplastics reduced the soil N and P content, with PE slightly increasing the DOC content, while PLA and aging-PLA significantly increased DOC by 21.13 and 24.04%, respectively. Microplastics also decreased soil enzyme activity, with aging-PLA having a somewhat stimulatory effect on enzyme activity compared to PLA. Furthermore, microplastics reduced the soil bacterial diversity index and altered the community structure of dominant bacterial species, with DOC content and FDA hydrolase being the main factors influencing the soil bacterial community. Bacteria were most sensitive to PLA, and the stability of the bacterial microbial network structure decreased, although aging reduced the negative impact of PLA on the bacterial community. This study contributes to our understanding of the ecological risks posed by biodegradable plastics and their aging processes on the environment.

Lake regime shift theory provides effective support for managing lake eutrophication. However, there are limited studies on identifying lake regime status using mathematical methods. Based on the similarities in characteristics and evolutionary patterns of lake ecosystems, and utilizing long-term lake water ecological monitoring data, this study introduces a method for evaluating lake regime status using total nitrogen (TN), total phosphorus (TP), and chlorophyll-a (Chl-a) as evaluation indices. Taking Poyang Lake as an example, the lake regime status was evaluated. The results showed that: The weights of total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl-a) in Poyang Lake were 0.207, 0.234 and 0.559, respectively, with Chl-a being the main controlling factor for evaluating the lake regime. The lake regime of Poyang Lake is in the Algae-Macrophytes Coexist state. The similarity assessment method has been proven effective for determining a lake regime using sparse water eco-environmental data.

Lake eutrophication has become a significant water environmental issue worldwide. In order to further explore the mechanism of hydrologic connectivity on lake eutrophication and effectively control it, this study selected Poyang Lake, Junshan Lake, Chi Lake, Taibo Lake, and Yao Lake with varying degrees of hydrological connectivity in the Poyang Lake region as research subjects. The study utilized the comprehensive Trophic Level Index (TLI) method to assess the eutrophication of lakes. It also examined the impact of hydrological connectivity on eutrophication evaluation indices and the eutrophication state on a spatiotemporal scale. The results showed that the change in the hydrological period has little effect on the eutrophication of lakes, whether they are connected or obstructed. Except for Yao Lake, which was in a moderately eutrophic state (60, 70], the other four lakes were in a mildly eutrophic state (50, 60], consistent with the Trophic State Index (TSI) evaluation results. The eutrophication evaluation indices of obstructed lakes were significantly different from those of river-connected lakes. The change in eutrophication evaluation index of obstructed lakes was more likely to be influenced by human factors, whereas that of rivers-connected lakes was closely associated with hydrological connectivity. At present, there is a risk of a cyanobacteria bloom outbreak in Poyang Lake and its surrounding lakes. Therefore, this study suggests that strict control of point and non-point source pollution in the lake region, along with the scientific and reasonable formulation of a cultivation model, will effectively prevent lake eutrophication and cyanobacteria bloom outbreaks. This study provides theoretical support for investigating the mechanisms of lake eutrophication.

Background Poyang Lake is the largest freshwater lake in China, and there are several studies on the composition and diversity of bacteria in Poyang Lake, while few quantitative studies were carried out on the response of the bacterial community to environmental factors during the extreme flood season in Poyang Lake. Methods The connected-lake heterogeneity of bacterial community composition (BCC) was investigated in Poyang Lake during the flood season in 2020. Illumina high-throughput sequencing technology was used in this study. Results The bacterial community structure in the water was different from that in the sediment of Poyang Lake during extreme flood seasons. The bacterial diversity in water was much lower than that in sediment. In the water column, the dominant phyla were Actinobacteriota, while the composition of bacteria in sediment was more complex than that in water, and the dominant phyla in sediment were Proteobacteria, Chloroflexi, Acidobacteriota, and Actinobacteriota. The bacterial diversity in the water of Poyang Lake showed seasonal dynamics, while no seasonal variation of bacterial communities in sediment was observed. The bacterial community structure in the sediment from the two bays and channel areas of Poyang Lake can be distinguished from each other. The microbial diversity in sediment gradually increased from the Sancha Bay to the Zhouxi Bay and then to the channel, but the total nitrogen (TN) concentration in sediment (STN) and the total phosphorus (TP) concentration in sediment (STP) showed opposite trends. This might be due to the anthropogenic disturbances from the extreme flood. The bacterial community structure in, water column was significantly correlated with WT, NH4-N, STP, SOM, Chl a, DO, TP, and Eh, while the bacterial community structure in sediment was significantly correlated with SOM and STP. Conclusion The bacterial community structure in water was greatly different from that in sediment in Poyang Lake during extreme flood seasons. The bacterial community structure in the water column was not only sensitive to the geochemical characteristics of the water but also affected by some nutrient concentrations in the sediment. During the wet seasons, bacterial diversity was only affected by SOM and STP.

Microcystis aeruginosa (M. aeruginosa) causes massive blooms in eutrophic freshwater and releases microcystin. Poyang Lake is the largest freshwater lake in China and has kept a mid-nutrient level in recent years. However, there is little research on microcystin production in Poyang Lake. In this study, water and sediment samples from ten sampling sites in Poyang Lake were collected from May to December in 2020, and from January to April in 2021 respectively. Microcystis genes (mcyA, mcyB, 16 s rDNA) were quantified by real-time fluorescence quantitative PCR analysis, and then the spatial and temporal variation of mcy genes, physicochemical factors, and bacterial population structure in the lake was analyzed. The relationship between the abundance of mcy genes and physicochemical factors in water column was also revealed. Results indicated that the microcystin-producing genes mcyA and mcyB showed significant differences in spatial and temporal levels as well, which is closely related to the physicochemical factors especially the water temperature (p < 0.05) and the nitrogen content (p < 0.05). The abundance of mcy genes in the sediment in December affected the abundance of mcy genes in the water column in the next year, while the toxic Microcystis would accumulate in the sediment. In addition to the toxic Microcystis, we also found a large number of non-toxic Microcystis in the water column and sediment, and the ratio of toxic to non-toxic species can also affect the toxicity production of M. aeruginosa. Overall, the results showed that M. aeruginosa toxin-producing genes in Poyang Lake distributed spatially and temporally which related to the physicochemical factors of Poyang Lake.

Microcystis aeruginosa causes massive blooms in eutrophic freshwater and releases microcystin. Poyang Lake is the largest freshwater lake in China and has kept at a mid-nutrient level in recent years. However, there is little research on microcystins production in Poyang Lake. In this study, water and sediment samples from ten sampling sites in Poyang Lake were collected from May to December in 2020, and from January to April in 2021 respectively. Microcystis genes ( mcyA,mcyB,16s rDNA ) were quantified by real-time fluorescence quantitative PCR analysis,and then the spatial and temporal variation of mcy genes, physicochemical factors and bacterial population structure in the lake was analyzed. The relationship between the abundance of mcy genes and physicochemical factors in water column were also revealed. Results indicated that the microcystin-producing genes mcyA and mcyB showed significant differences in spatial and temporal levels as well, which is closely related to the physicochemical factors especially the water temperature(p < 0.05) and the nitrogen content(p < 0.05). The abundance of mcy genes in the sediment in December affected the abundance of mcy genes in the water column in the next year, while the toxic Microcystis would accumulate in the sediment. In addition to the toxic Microcystis , we also found a large number of non-toxic Microcystis in the water column and sediment, the ratio of toxic to non-toxic species can also affect the toxicity production of Microcystis aeruginosa . Overall, the results showed that Microcystis aeruginosa toxin-producing genes in Poyang Lake distributed spatially and temporally which related to the physicochemical factors of Poyang Lake.

The interpretation of environmental effect on phytoplankton growth is not straightforward, especially in ecosystems with high variation in hydrological conditions due to confounding variables. Lake Poyang is characterized by high fluctuation of water level (WL) due to its free connection to the Yangtze River. High frequency (weekly) and long-term (2009–2018) samplings were conducted in Lake Poyang resulting in 170 samples. Our study aimed to illustrate that whether the key factors determining phytoplankton growth change with WL. Furthermore, the impact of WL on phytoplankton was also detected. Six periods were classified in our study, i.e., dry season, raising period (I and II), wet season, and falling period (I and II) based on WL variation. Environmental characteristics were significantly (P < 0.01) different among these periods with the exception of orthophosphate. Based on the whole data set, water temperature (WT) was the critical parameter affecting phytoplankton growth. However, according to time series analysis, the key factors varied in different periods. Underwater light condition, which was represented by Secchi depth (SD), was the most critical factor controlling phytoplankton growth, especially in the periods with relatively high WL and WT (i.e., raising period II, wet season, and falling period I). The role of water temperature on phytoplankton was more evident in falling periods. In dry season with the lowest WL, total phosphorus limited phytoplankton growth. Regarding WL, its impact on phytoplankton was mainly through change in environmental parameters, such as water flow velocity, water transparency, and nutrients. Furthermore, time series analysis well simulated phytoplankton chlorophyll a in Lake Poyang, with larger R²adj (except raising period II and falling period II) and lower model error in all 6 periods. Our results revealed that the critical factors controlling phytoplankton growth were various with WL. Additionally, time series analysis will benefit local water resource management.