Effects Of Allochthonous Dissolved Organic Carbon Subsidy On Biodiversity And Temporal Stability Of Freshwater Zooplankton Communities

Freshwater ecosystem is strongly facing the impacts of global climate change.One of the important issues is the large amount of allochthonous dissolved organic carbon(DOC)subsidy to the lake system that would cause the water become "browning".While,the impacts of this browning on biodiversity and ecosystem function of lake ecosystems are not well understood in the future scenario.In this study,we investigated the effects of increased input of allochthonous dissolved organic carbon on zooplankton diversity and community stability based on the mesocosm experiments.Meanwhile,we studied the response of zooplankton carbon source utilization to the increase of allochthonous dissolved organic carbon input via using the stable isotope analysis,thus try to explore the potential mechanism of zooplankton utilization of allochthonous organic carbon.The main results are as follows:1.The abundance of zooplankton showed significant difference among different allochthonous dissolved organic carbon concentration gradients(df = 5,P < 0.05).With the increase of carbon supplement concentration,the zooplankton abundance reached the peak earlier,and the peak of zooplankton abundance decreased The biomass of zooplankton showed significant difference among different allochthonous dissolved organic carbon concentration gradients(df = 5,P < 0.05).With the increase of carbon supplement concentration,the zooplankton biomass reached the peak earlier,and the peak of zooplankton biomass decreased.The biological diversity index(Shannon diversity,Taxa richness,Pielou evenness,Simpson diversity index)was not significantly affected by different concentrations of dissolved organic carbon(Shannon diversity:df = 5,P = 0.063;Taxa richness :df = 5,P = 0.104;Pielou evenness :df = 5,P = 0.069;Simpson index:df = 5,P = 0.267),but the biological diversity index(Simpson diversity,Shannon diversity,Taxa Richa)was significantly different with different time periods(Simpson index:df = 5,P < 0.05;Shannon diversity:df =5,P < 0.01;Taxa richness :df = 5,P < 0.01),and there was a downward trend with the sampling time.Results show that the zooplankton diversity decrease is due to the main dominant species in the process of experiment(Plalyias militaris,Copepod nauplii,Thermocyclops taihokuensis,Sinocalanus dorrii)of dominance,driven by the experiments,the experiment first sampling Copepod nauplii dominance accounted for45.34%,In the fifth sampling,the dominance ratio of Thermocyclops taihokuensis accounted for about 50%,and the changing dominance ratio led to the decrease of zooplankton biodiversity.2.No significant difference was observed in the effect of different concentrations of allochthonous dissolved organic carbon on the stability of zooplankton community(df = 5,P = 0.312),and the total stability index of zooplankton did not change significantly with time(df = 5,P = 0.134),but the overall stability index fluctuated continuously with time.At the same time,the zooplankton community was in a stable state under different concentrations of allochthonous dissolved organic carbon treatment.Therefore,we concluded that different allochthonous dissolved organic carbon had no significant effect on the stability of zooplankton community.3.With the increase of carbon supplemental concentration,the utilization of allochthonous carbon in zooplankton decreased significantly(df = 5,P < 0.01).Under the condition of 10 mg/L allochthonous carbon addition,the utilization rate of allochthonous carbon in zooplankton was the highest,ranging from 56.37 to 66.74%,with an average of 60.03%.Under the condition of 30mg/L allochthonous carbon addition,the utilization rate of allochthonous carbon in zooplankton was the lowest,ranging from 15.00 to 41.23%,with an average of 27.92%.