| The global climate is getting warmer and warmer,but at present,many studies on the impact of temperature on the lake phytoplankton are confined to take daily average temperature as the unique indicator.Research indicates that the minimum temperature increases far more quickly than the maximum temperature in most parts of the Northern Hemisphere,that is to say,the trend of increasing temperature is asymmetric.Studies have shown that asymmetric change of temperature has a significant impact on terrestrial ecosystems,particularly agro-ecological system,but the impact of asymmetric warming on lake ecosystem has been neglected to some extent.The paper firstly uses history data to analyze the impact of daily minimum temperature on the change of phytoplankton community in Lake Taihu and Lake Pyh?j?rvi,combined with inner-laboratory experiment,trying to explore the impact of daily minimum temperature on the growth,photosynthesis and respiration of Microcystis aeruginosa,one of the dominant species in Lake Taihu.The main conclusions are as follows:1?Microcystis sp.is the most dominant species in the summer of 1992-2012 in Lake Taihu and the richness of phytoplankton reduces.The most significant factor that affect the summer phytoplankton cummunity is conductivity and the second significant factor is daily minimum temperature,which means that meteorological factors have produced relatively large impact on the change of phytoplankton community in the summer of 1992-2012 in Lake Taihu.Among the meteorological factors,daily minimum temperature is the most significant.2?The dominant species changes in the summer of 1960s-2012 in Lake Pyh?j?rvi and also the total amount of biomass increases.The most significant factor that affect the summer phytoplankton community is daily minimum temperature,followed by the concentration of total nitrogen,wind speed and daily average temperature.Changes of phytoplankton community are mainly affected by the meteorological factors and daily minimum temperature is the most significant factor among them.3?Fv/Fm?ETRmax and ? firstly increase and then decrease in the course of the whole experiment and have high fluctuation in log phase.The maximal value of the three indexes appear in the daytime warming group,followed by the combined warming group and the nighttime warming group.The difference of photosynthesis indexes are not significant in the three experiment groups.Nighttime warming can significantly accelerate cell division and increase the speed of proliferation of Microcystis aeruginosa in log phase and also can increase the total number of the cells and the number of cells in division.The effect of 1 °C nighttime warming have a certain degree of delay when compared with 2 °C nighttime warming.4?The respiratory rate of Microcystis aeruginosa increases with the temperature set from 16 °C to 30 °C.The respiration rate increases when the ambient temperature is much closer to the optimum temperature and respiration rate of Microcystis aeruginosa per unit chlorophyll a is in the magnitude of 10-2-10-1 molO2 / h.?gchla. |
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