| Responses of marine primary and secondary produce processes to ocean global changes are of general importance in order to understand how marine biological production,carbon sinking proecesses and manne ecosystem services will change under multiple anthropogenic drivers.Therefore,it is essential to investigate responses of primary and secondary producers to ocean acidification(OA),warming,and enhanced ultraviolet radiation(UVR).In this study,biochemistry,physiological,and ecological responses of planktonic organisms to the environmental changes were examined by indoor controlled experiment,outdoor microcosm experiments,field mesocosm tests,and research cruise ship-board tests.The main results are as follows:1.Coastal diatoms showed interspecific diferential responses to OA,with the growth of Ditylum brightwellii being negatively affected by high pCO2 and lower pH treatment,that of Thalassiosira rotula unaffected but the growth of Chaetoceros debilis was stimulated by the treatment.Nevertheless,Thalassiosira rotula showed a competitive advantage in interspecific competition and this advantage was unaltered by OA.2.OA acclimation affects the thermal reaction norm of the diatom D.brightwellii,decreasing its optimal growth temperature and maximal growth rate under the elevated pCO2(1000 ?atm)condition after 20 generations.The effective quantum yield and maximum electron transfer rate of PSII decreased with increased temperature,with a further decrease being found under the high pCO2.3.The copepod Acartia pacifica up-regulates its grazing and respiration rates under the condition of OA and warming.Solar UVB have no effects on grazing rate,while its grazing and respiration increased under the high pCO2(1000 ?atm),warming(+4?)and decreased food quality(decreased POC/PON in the algal cells).And,A.pacifica has the ability to sense pH change and this ability was deactivated by high levels of UVR exposures.4.Coastal primary and secondary production processes showed relatively less sensitivity to environmental changes.During the microcosm and mesocosm experiments performed under natural fluctuating conditions,OA and UVR appeared to influence little the growth and productivity of coastal phytoplankton,but temperature changes significantly affect it.Phytoplankton fatty acid(FA)content and composition of phytoplankton assemblages were unaltered by OA,though they differed in different growth phases.Mesozooplankton,mainly copepod,can maintain their ingestion of nutritional FAs by regulating their grrazing rates5.Daily primary productlivity(PP)of surface seawater phytoplankton asse1blages in the South China Sea was stimulated,unaffected or inhibited by UVR depending on weather conditions and seawater chemistry.OA treatment decreased PP in oligotrophic waters.Solar UVR increased primary production(PP)in surface water of Pearl River estuary with decreased UVR intensity.Low levels of UVA stimulated PP while UVB decreased it.Future OA impact on surface PP in South China Sea is significantly correlated with nutrients availability,being stimulating in estuary plume,upwelling system and coastal waters but inhibiting in oligotrophic waters due to reduced nutrients availability.Our results demonstrate that marine diatoms showed interspecific difference in responses to OA;primary and secondary production process responses to OA are modulated by temperature,nutrients availability and UVR.The key findings are:1)OA altered thermal reaction norm of diatoms;2)OA,warming and decreased food quality increased mesozooplankton grazing and respiration;3)OA showed limited effects on microalgal fatty acids.However,these eco-physiological responses of phytoplankton and zooplankton to marine environmental changes can differ in different regions and under different climate conditions.Future study on effects of ocean climate changes on plankton productivity should focus more on multiple stressors to explore the uncertainties and to explain controversial findings. |
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