Impact of rising CO 2 on freshwater phytoplankton

Transcription

1 Impact of rising CO 2 on freshwater phytoplankton from cell to bloom dynamics CO 2 CO 2 HCO 3 - CO 2 HCO 3 - CO 2 (CH 2 O) n Jolanda Verspagen

2 Dissolved Inorganic Carbon and phytoplankton atmosphere water CO 2 CO2 H2O H HCO 3 - HCO 3 = bicarbonate 2- CO 3 = carbonate DIC CO 2 HCO 3 CO 2 3 CO 2 2H 3 Most species can use both CO 2 and HCO 3 - The affinity and preference for CO 2 and HCO 3- differs between species

3 Sandrini et al. 2014, The ISME Journal; Huisman et al., in prep. Cyanobacterial Carbon Concentrating Mechanisms Outer membrane Plasma membrane Cyanobacteria can induce CCMs that allow them to take up CO 2 and HCO 3 - more efficiently CO 2 ATP NADPH HCO - 3 CA HCO - 3 CO 2 HCO 3 - Na + RuBisCO β-carboxysome CO 2 uptake HCO 3- uptake NDH-I 3 NDH-I 4 BCT1 SbtA BicA Thylakoid membrane Affinity Flux rate high low low high high low high low low high

4 Chemostat experiments at low and high pco 2 Inflow: dissolved nutrients (HCO 3-, NO 3-, PO 4 3-, etc.) Outflow: remaining nutrients + phytoplankton Microcystis air + CO 2(g) Monitoring: population density, light, ph, DIC, Alk, C:N, DW,

5 Modeling carbon uptake and growth resources phytoplankton cell population [CO 2 ], [HCO 3- ], light uptake storage C growth Carbon uptake rate increases with increasing [CO 2 ], [HCO 3- ] and light availability Growth rate increases with increasing carbon storage

6 Model differential equations Population dynamics dxi dt growth mortality i = 1,, n Cellular carbon storage dq i dt uptake of C respiration growth dilution Carbon chemistry d DIC dt diffusion dilution phytoplankton uptake phytoplankton respiration dalk dt dilution NO uptake PO uptake 2 uptake 3 4 SO4 Actual [CO 2 ], [HCO 3- ] and [CO 3 2- ] depend on ph and alkalinity

7 Measurement of CO 2 and HCO 3- uptake kinetics CO 2 and HCO 3- uptake of the cyanobacterium Microcystis (100 ppm) (2000 ppm) Microcystis relies largely on HCO 3- uptake Ji et al., in prep

8 Dynamics of bloom development Low pco 2 (200 ppm) High pco 2 (1200 ppm) Low pco 2 : - Low [CO 2 ] - High ph High pco 2 : - High biomass - Low light availability Verspagen et al. 2014, PloS one

9 Impact of rising pco 2 on phytoplankton and resources Increasing pco 2 increases phytoplankton population density At low pco 2, CO 2 availability limits phytoplankton growth At high pco 2, light availability limits phytoplankton growth Verspagen et al. Plos One, 2014

10 How will rising CO 2 concentrations affect blooms in eutrophic lakes?

11 Extrapolation to natural eutrophic waters [DIC] IN I IN d upscaling from chemostat to lakes pco 2 I IN = 400 mmol photons m -2 s -1 Lower CO 2 exchange rate Lower dilution rate Microcystis 5 m Additional mortality rate 95% of dead phytoplankton is remineralized, 5% is buried permanently

12 Model predictions Increase in pco 2 expected in this century Prediction: Rising pco 2 will intensify phytoplankton blooms in eutrophic waters Verspagen et al. 2014, PloS One

13 Sandrini et al. 2014, The ISME Journal; Huisman et al., in prep. Microcystis strains can differ in their CCM genotype Carbon uptake systems CO 2 uptake HCO 3- uptake NDH-I 3 NDH-I 4 BCT1 SbtA BicA Affinity Flux rate high low low high high low high low low high SbtA strain CCM genotypes in Microcystis BicA strain BicA + SbtA strain

14 Changes in bloom composition with increasing pco 2 Chemostat experiments Lake Kennemermeer Low pco 2 (100 ppm) High pco 2 (2000 ppm) In mixtures of Microcystis, strains with the high-flux bica transporter become stronger competitors at high CO 2 concentrations Increasing CO 2 Sandrini et al., 2016, PNAS

15 How does a dense phytoplankton bloom influence the atmospheric CO 2 flux in a shallow hypertrophic lake? CO 2

16 Study site: Amstelveense Poel

17 Data collection Mid May to mid November 2016 High-frequency data (15-30 min interval): Dissolved CO 2, dissolved O 2 Temperature, ph, Chlorophyll a fluorescence CO 2 flux (ECS), meteo data Weekly data: Chlorophyll a Phytoplankton species composition Nutrients (inorganic, organic, total N&P) DIC, alkalinity

18 Lake trophic state and CO 2 saturation Paul Peter Paul: oligotrophic supersaturated Peter: mesotrophic Wilkinson et al 2016, Geophysical Research Letters Amstelveense Poel Amstelveense Poel: hypertrophic Day of Year Verspagen et al., in prep undersaturated

19 Lake trophic state and CO 2 flux Paul Peter Paul: oligotrophic CO 2 source Wilkinson et al 2016, Geophysical Research Letters Amstelveense Poel Amstelveense Poel: hypertrophic Day of Year Verspagen et al., in prep CO 2 sink

20 Ecosystem productivity Based on changes in: dissolved inorganic carbon (DIC) dissolved oxygen (DO) Respiration (R) Increase in DIC at night Decrease in DO at night R NEP Net ecosystem production (NEP) Decrease in DIC during day Increase in DO during day NEP DIC = - NEP DO

21 CO 2 flux versus NEP DIC Expectation: when productivity is high (high NEP), the lake is a CO 2 sink Respiration > productivity CO 2 source Productivity > respiration CO 2 sink Lake Amstelveense Poel remains a CO 2 sink when respiration > productivity in fall Verspagen et al., in prep

22 Conclusions Rising CO 2 concentrations are expected to intensify cyanobacterial blooms and change bloom composition in eutrophic lakes Dense phytoplankton blooms can turn a lake into a CO 2 sink

23 Thanks to: Bas van Beusekom Ramon den Boer Jef Huisman Jason Ji Maria Meijer Giovanni Sandrini Arie Vonk Dedmer van de Waal Josh Dean Han Dolman Ko van Huissteden Ron Lootens Hoogheemraadschap van Rijnland Gemeente Amstelveen and many others Amsterdamse Bos