We conducted a seasonal survey on phytoplankton and environmental factors in Yilong Lake from summer, 2020 to spring,2021 to uncover the seasonal pattern of phytoplankton community structure and biomass, and further identify the driving forces of bottom-up and zooplankton’s top-down effect in mediating phytoplankton variations through multivariate analysis. The results showed that the phytoplankton’s biomass in Yilong Lake ranged from 7.12mg/L to 66.07mg/L, with the highest value in September and the lowest value in December. The phytoplankton community was dominated by Cyanophyta, which contributed to 42.91% to 95.67% of total phytoplankton biomass. Raphidiopsis raciborskii, absolutely predominated during the investigation period(23.43%~84.30%), reflecting its strong competitive advantages. The ANOSIM and Kruskal-Wallis analyses indicated that there existed significant temporal fluctuation in phytoplankton community structure and biomass(P<0.05). The Spearman’s correlation analysis revealed that the biomass of phytoplankton, Cyanophyta and R. raciborskii were all positively related to total phosphorus(P<0.05), total nitrogen and water temperature and negatively related to transparency and ammonia nitrogen(P<0.05), but had no significant correlation with zooplankton biomass(P>0.05). The RDA results showed that total phosphorus, total nitrogen, silicate, water temperature and water depth were among the significant factors in driving phytoplankton community in Yilong Lake. The results of variation partitioning further revealed that the bottom-up effect (water temperature, nutrients and water depth) and top-down effect (zooplankton community) accounted for 20.30% and 0.20% of the total variance independently with a shared portion of 5.80%. Therefore, the bottom-up effect had a greater impact on variations in phytoplankton community than the top-down effect by zooplankton in Yilong Lake. This may be because zooplankton in Yilong Lake had small mean body length (ZB/ZA:0.0019±0.0018) and relatively low biomass (0.56±0.39mg/L), and thus resulting in the weak grazing pressure on algae (ZB/PB:0.0303±0.0271). Our results will provide scientific data for the ecological assessment and integrated watershed management of Yilong Lake.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |