Phytoplankton Community Succession And Nutrition Absorption Response To Warming In Mesocosms

Shallow lakes are highly vulnerable to damages caused by human activities and warming trends.Over the past one hundred years temperature has increased about 0.5 °C,and nearly half of the heating effect occurred in the past 30 years.Some research confirmed that warming effect creatures through multiple factors,which can lead to irreversible ecological succession or extinction phenomenon and a trend of ecological deterioration increased year by year.At present,the study of warming usually aimed at the effect on terrestrial ecosystem.How could warming affect phytoplankton on characteristics of nutrients absorption and community structure remain unknown.In order to investigate the response of phytoplankton to warming interacts with environmental factors and phytoplankton nutrient uptake,we set up outdoor mesocosms in order to discuss the impact of climate warming and phosphorus availability on phytoplankton community structure and nitrogen uptake,and discuss the impact of climate warming and the bioturbation of carp on phytoplankton carbon and nitrogen uptake.The main results as follows:?1?Warming and phosphorus addition can significantly promote the phosphorus concentration and biomass of phytoplankton during autumn and winter increasing in water column.Phytoplankton recruitment results show that Bacillariophyta recruitment increased earlier in those treatments with elevated temperatures?T and TP?during the winter and spring.At the same time,warming increasing with phosphorus addition could significantly increase the recruitment rate of blue-green algae from sediment in the spring,which may result in blue-green algae formed competition superiority in water column.?2?Warming and phosphorus addition could significantly influence on phytoplankton community composition.Warming could significantly promote the Chlorophyta density increasing and Cryptophyta density decreasing.Therefore,synergistic effects of warming and eutrophication may promote blue-green dominance and persistence in water column.?3?By using ¹⁵N tracer techniques in study simulation system nitrogen absorption characteristics of phytoplankton,we found that phosphorus addition slightly promoted the phytoplankton nitrate uptake velocity?V and r?and relative preference index?RPI?but prolonged the nitrate uptake turnover time?TT?.Warming could increase the ammonium uptake velocity and the relative preference index of phytoplankton but dreasing the ammonium turnover time.Hence,warming and eutrophication increased the capacity of phytoplankton for ammonium uptake and their affinity at low substrate concentrations.The results of phytoplankton nitrogen uptake dynamics show that,compared with nitrate uptake,phytoplankton ammonium absorption dynamics showed higher maximum uptake rate?Vmax?and lower half-saturation constant?Ks?in those treatment of phosphorus addition and elevated temperature?P and TP?.?4?Bioturbation of young benthic fishes promoted the nitrogen and phosphorus nutrients and algae biomass increasing in water column under warming through disturbing sediment,feeding large zooplankton and excretion.Bioturbation of carp slightly increased the phytoplankton nitrate uptake velocity?V and r?in spring,and obviously increased the phytoplankton nitrate and ammonia uptake velocity?V and r?in summer.Nitrate uptake velocity increasing significantly higher than ammonia uptake velocity.Therefore,warming and the bioturbation of carp increased the capacity of phytoplankton nitrate uptake.In addition,the phytoplankton absorption characteristics of carbon showed that warming and benthic fishes disturbance could significantly promote phytoplankton absorption of bicarbonate during spring and summer.