In aquatic ecosystems, the dynamics of ecological parameters play an important role in community organizations. To understand the seasonal variation in the phytoplankton community in Lake Wuchang, Anhui Province, water samples were collected in three different hydrological periods (dry season, normal season, and wet season) from December 2019 to August 2020. The dominance value (Y), niche width (B_i), niche overlap (O_ij), variance ratio method (VR), chi-squared test (χ²), and association coefficients were used to analyze the niche and interspecific association with respect to the dominant phytoplankton species in different hydrological periods, while the redundancy analysis method (RDA) was used to distinguish the key driving environmental factors for the dominant phytoplankton species. The results showed that 308 species belonging to 8 phyla were identified, of which 13 species from 4 phyla were the dominant species. From the dry season to wet season, the dominant species changed from Bacillariophyta to Cyanophyta, while Synedra acus was the dominant species throughout the hydrological periods. The niche width of the dominant species varied from 1.77 to 6.65, and the niche width of Dinobryon was the lowest, while that of Synedra acus was the highest. The niche overlap showed temporal and spatial differences, of which 30 dominant species pairs were greater than 0.600, indicating that they occupied the environmental resources in a highly similar way. The interspecific association results showed that there was a significant positive correlation between the dominant species, especially in normal and wet seasons. Only 10 of the 48 dominant species pairs had significant associations based on the χ² test, and two pairs had negative associations in the wet season, which might be related to the hydrological condition in the wet season. According to redundancy analysis, NO₃⁻-N, NH₄⁺-N, PO₄^3--P, water depth (WD), and water temperature (WT) were the key environmental factors affecting the phytoplankton community variation in Lake Wuchang. This paper provides a new perspective for the study of the early warnings regarding the cyanobacteria bloom outbreak, and the management and protection of the water ecological environment in shallow lakes in the middle and lower reaches of the Yangtze River.

Numerous studies have shown that thermal tolerance and intestinal heat resistance are strongly associated with temperature acclimation. However, few reports have successfully conducted similar research on fishes from the Qinghai–Tibetan Plateau, an area that is facing the threat of climate warming. Therefore, the present study determined the growth, thermal tolerance, and intestinal heat stress (exposure to 30°C) responses in juveniles of a Tibetan fish, Oxygymnocypris stewarti, acclimated to three temperature levels (10°C, 15°C, and 20°C, named as T10, T15, and T20, respectively) for 30 days. The fastest growth was recorded in the T15 group. At 1°C/30 min heating rate, the critical thermal maximum (CT_Max) ranged from 31.3°C to 32.3°C, and the lethal thermal maximum (LT_Max) ranged from 31.8°C to 32.6°C among the three acclimation temperatures. According to the results of thermal tolerance tests, the heat stress temperature was set to 30°C. When the water temperature reached 30°C, the expression of the intestinal heat shock protein 70 (HSP70) gene as well as the intestinal microbiome and histology of experimental fish were monitored at 0, 2, 6, and 12 h. The expression of HSP70 reached the highest level at 2 h in all three temperature treatments. The histological analysis showed damage to intestinal cells, including diffuse infiltration of lymphocytes, villi epithelial cell swelling, decrease of intestinal villi length, and cytoplasmic light staining at 2 h in all three temperature treatments. In terms of the intestinal microbiome, phyla Proteobacteria and Firmicutes dominated the treatments at each monitored time in the T10 and T15 groups and at 0 h in T20 group, while phyla Fusobacteria, Proteobacteria, and Cyanobacteria were dominant in treatments at 2, 6, and 12 h in the T20 group. The overall results indicated that acclimation temperature could affect the growth, thermal tolerance, and intestinal heat stress response of O. stewarti juveniles. As the first report on intestinal heat stress response associated with temperature acclimation in a Tibetan fish, this study will help to understand the potential effects of climate change on highland fishes.

This study focused on monitoring the dynamics of bacterial communities and assessment of the influences of physicochemical parameters during a culture cycle in black carp polyculture ponds. Our results showed high variation in microbial diversity and microbial composition in the water column during the culture period. Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant phyla, while the abundances of the phyla Cyanobacteria, Firmicutes, and Bacteroidetes changed in different months. Moreover, 13 abundant genera with significant difference were found between different months. Thus, samples in different months were divided into three groups according to principal coordinate analysis (PCoA) and unweighted pair-group method (UPGMA) clustering results. RDA showed that total nitrogen (TN), total phosphorus (TP), phosphate (PO₄³⁻-P), nitrate (NO₃⁻-N), temperature (T), dissolved oxygen (DO), and pH significantly shaped the microbial community composition in different months. While Pearson correlation coefficient showed that T, SD, and pH were strongly correlated to the dominant genera. Considering some genera are potential pathogenic bacteria, we could manage the black carp pond by quickly monitoring the water temperature and SD in the future.

Lake phytoplankton communities are affected by environmental and spatial factors. We studied the relative importance of environmental and spatial factors on the phytoplankton community assembly in Lake Wuchang across three hydrological seasons, which were divided into dry (December to March), normal (April to June, October to November) and wet seasons (July to September) based on the water level and depth. Spatial and temporal patterns of environmental factors and phytoplankton community composition and diversity were studied using Kruskal–Wallis test, Wilcoxon test and NMDS. CCA, Mantel and partial Mantel tests, and PLS-PM were used to investigate the effects of environmental and spatial factors on phytoplankton community characteristics. Results showed that phytoplankton assemblages at the eight study sites were composed of totally 244 species belonging to 9 phyla, which changed from Bacillariophyta and Chlorophyta to Cyanophyta across the whole hydrological period. There was significantly higher abundance and biomass in the normal and wet seasons than that in the dry season. Phytoplankton alpha diversity exhibited uniform temporal distribution patterns with higher values in the dry season than in the normal and wet seasons. The Mantel and partial Mantel tests revealed that environmental (physicochemical conditions of lake water) and spatial factors (geographic distances among sites) jointly affected the phytoplankton community structure and beta diversity across the hydrological seasons, while spatial factors were more important in the wet season. Partial least squares path models showed that spatial factors exhibited a significant positive correlation with the phytoplankton diversity with the path coefficients of 0.53 and 0.71 in the normal and wet seasons, respectively. Phytoplankton composition had significant correlation with on phytoplankton diversity with the path coefficient of −0.75 and 0.61 in the normal and wet seasons, respectively. Our findings revealed that both environmental and spatial factors affected the phytoplankton community assembly in Lake Wuchang. Environmental factors played a more important role in the dry season, while spatial factors were more important in the wet season. With the exception of the abiotic factors (environmental and spatial), the impacts of biotic factors on phytoplankton community cannot be ignored. Therefore, it is also necessary to strengthen further research on the top-down control over phytoplankton communities in Lake Wuchang.