Responses Of Physiological Function To Increased NH₄⁺Concentrations Of Seawater Under Different Environmental Conditions Inmarine Macroalgae

The marine environment is changedasGlobal warmingwhileseawater eutrophicationresulted in NH4+increased. This study is targeted to investigate correlations between growthand photosynthesis function of three kinds marine macroalgaes like Gracilaria lemaneiformis,Ulva lactuca.L and Porphyra haitanensis. To simulating the greenhouse effect on seaweed，different CO（2atmosphere and700μL/L）and NH4+level was set. FW, RGR, Chla, Car, PE andPI data were collected to analyze seaweed growth effects and physiological functions ineutrophic coastal water. Results were as follows:1.At20℃, different seawater NH4+levels were set to cultivate Ulva and Gracilarialemaneiformis. Result showed a low NH4+leve（l0－480μmol/L）couldsignificantly promoteGracilaria lemaneiformis growth and RGR has the maximum （1.5%d-1）at480μmol/L.When above480μmol/LGracilaria growth was restrained and NH4+was negative correlatedwith Chla, Car, RGR (p<0.05), respectively. In the same treatment, Gracilaria wasprofromed more survivability than Ulva for NH4+.UlvaChla, Car,RGRvaluesweresignificantly higher than Gracilariain the sametreatment, physiological and biochemicalindications of Ulvaappropriate NH4+concentration has a wider range than Gracilaria: Chla,Car, RGR in Ulva was significantly higher than those in Gracilaria. In all treatments, α forUlva was negatively correlated withcultivating time. This phenomenon indicates that the highconcentration NH4+has inhibitory effect on macroalgae and this inhibitory accumulated astime goes by.2. This study investigated the correlatons of different CO2and NH4+concentrations inseawater on the growth and photosynthesis of Porphyra haitanensis (Rhodophyta). The algaewere cultured for7days in natural seawater supplied with5different NH4+concentrationsand aerated with atmospheric air and elevated CO2(700μL/L). Results showed the highestgrowth of P. haitanensiswas observed at120μmol/L NH4+level, where the algaeoccurredhigher valueof pigments, maximal photochemical yield (Fv/Fm) and maximumrelative electron transport rates (rETRm) compared to other levels of NH4+in culture.Elevated CO2has enhanced the growth and photosynthetic performances of the algae.NH4+concentrations was negative correlated with the growth, photosynthetic pigments value, Fv/Fm, and rETRm (p<0.05), respectly. That was suggesting high levels of NH4+resulted inphysiological stress on P. haitanensis. However, reduction of RGR, Fv/Fm, and rETRmresulted from high NH4+levels were much slower when aerated with elevated CO2in culture.It can be induced that, increasing atmospheric CO2would alleviate the physiological tressresulted by high NH4+levels in P. haitanensis.3.To study correlations between temperature and NH4+concentration on growth,physiological effects of seaweeds, treatments were set as follows:（1）18℃+0μmol/LNH4+,（2）18℃+400μmol/LNH4+,（3）18℃+2000μmol/LNH4+,（4）18℃+4000μmol/LNH4+,（5）27℃+0μmol/LNH4+,（6）27℃+400μmol/LNH4+,（7）27℃+2000μmol/L NH4+,（8）27℃+4000μmol/L NH4+. Results showed: Haitanensis at18℃, NH4+concentration was negatively correlated with Chla, Car, PE, Fv/Fm, α and qN; At27℃, maximums were showed at400μmol/L NH4+level with PE（3.458mg/g）, rETRm（24.66）, qN （0.2183）while Chla, Car, Fv/Fmand α was negatively correlated with NH4+concentration, respectly. This phenomenon reveals that high temperatures could restainhaitanensis growth and strengthened as NH4+concentration increased.4. Ulva was cultured as follows:（1）10℃+0μmol/LNH4+,（2）10℃+400μmol/LNH4+,（3）10℃+4000μmol/LNH4+,（4）20℃+0μmol/LNH4+,（5）20℃+400μmol/LNH++4,（6）20℃+4000μmol/LNH4,（7）30℃+0μmol/LNH4+,（8）30℃+400μmol/L NH4+,（9）30℃+4000μmol/L NH4+. Positive correlations werefound between biomass and NH4+concentration, except30℃+4000μmol/L NH4+treatmentshows a negative correlation. At the same NH4+level, Chla has a maximum at20℃; and at20℃Chla was negative correlated with temperature. Negative correlations were foundbetween temperature and Car. At the same temperature, Chla、Car was negative correlatedwith NH4+concentration. At10℃and20℃, no correlation was found between Fv/Fm,andNH4+concentration; at30℃,NH4+concentration was negative correlated with Fv/FmandqN, respectly. Negative correlation was found between Ekand NH4+concentration except30℃＋400μmol/L NH4+and0μmol/L NH4+points. There was no significant differenceforRdunder different treatment.To sum up, result showed that seaweeds had different reactionsonNH4+levels. Among3kinds of seaweeds, Gracilaria was the most vulnerable on a high NH4+level and haitanensis was the second. Effects on different CO2level or temperature for seaweeds growth andphotosynthesis was differentiated. A low NH4+level could simulate seaweed growth, but ahigh level would lead to a decreasingalgae electron transfer rate and restrainingphotosynthesis. Increasing CO2concentration could ease restraint from high level NH4+toseaweeds.Over low temperatureorhigh temperature willrise the intimidationfroma highconcentrationNH4+on marine macroalgaes.