Physiological Responses Of Gracilariopsis Lemaneiformis To Multiple Environmental Factors Under Nutrient Limitation

Macroalgae live in marine all the year round.Their growth and development depend on the suitable ecological environment,and inevitably to respond to the stress of various environmental physicochemical factors.The current atmospheric elevated CO₂ concentration produces the greenhouse effect and leads to an increase CO₂ absorption by the world’s oceans,which promotes the acidification of the surface seawater and causes ocean acidification.In the future,this phenomenon may be further exacerbated,and potentially coupled with or accompanied by other environmental factors change.In particular,with the continuous improvement of marine environment comprehensive management level in China,the decline in the input of terrestrial nutrients in the offshore area,the high-density seaweed cultivation and the uncoordinated absorption ratio of N and P nutrients in the thalli,the phenomenon of nutrient deficiency in some coastal areas is becoming more and more serious.Variations in multiple environmental factors such as elevated CO₂ concentration,warming,N or P nutrient limitation and low salinity stress,may potentially affect macroalgal growth and photophysiology performance.Until now,most research regarding on the effect of nutrient limitation on macroalgae have focused on indoor or outdoor single-factor experiment.Relatively little is know about how algae respond to the combined effects of multiple environmental factors under the dual background of nutrient limitation and elevated CO₂ concentration.In this study,the economically important red algae Gracilariopsis lemaneiformis was used as the material,and multiple environmental factors such as temperature,CO₂ concentration and salinity were selected under outdoor natural light,which explored its physiological responses to multiple environmental factors under nutrient limitation.It was expected provide theoretical data support for the seedling field and selective breeding of G.lemaneiformis when the climate and environmental changes in the future.The details are as follows:1.Four nutrient gradients(HNHP:103.1μmol L^-1 N,10.1μmol L^-1 P;HNLP:103.1μmol L^-1N,0.1μmol L^-1 P;LNHP:3.1μmol L^-1 N,10.1μmol L^-1 P;LNLP:3.1μmol L^-1 N,0.1μmol L^-1P)and two CO₂ concentration levels（HC:1000μatm;LC:400μatm）were set up to study the coupling effects of N and P nutrient limitation and elevated-CO₂ on the growth and photophysiology of G.lemaneiformis.The results showed that P limitation had a significant effect on growth rate of G.lemaneiformis（P<0.05）.HC treatment had no significant effect on G.lemaneiformis growth under HP（P>0.05）but significantly reduced under LP（P<0.05）.Especially under LNLP the elevated CO₂ had the most significant negative impact on the growth of G.lemaneiformis（P<0.01）.LP decreased the net photosynthetic rate and r ETR of G.lemaneiformis（P<0.05）.Under LNLP the contents of photosynthetic pigment,SP and SC of G.lemaneiformis was significantly decreased（P<0.05）.The results suggested that P was the main nutrient limited factor on the growth of G.lemaneiformis.Nutrient limitation and ocean acidification synergically inhibited the growth and photophysiology performance of G.lemaneiformis.2.Two P nutrient gradients(HP:10.1μmol L^-1;LP:0.1μmol L^-1),two temperature gradients（HT:24℃;LT:20℃）and two CO₂ concentration levels（HC:1000μatm;LC:400μatm）were set up to study the effects of P nutrient limitation,warming and elevated-CO₂ on the growth and photophysiology of G.lemaneiformis.The results showed that the growth rate of G.lemaneiformis was significantly increased as temperature increment under HP（P<0.05）.HC significantly inhibited its growth（P<0.05）,while HT alleviated the inhibition effect of ocean acidification under LP.LP significantly decreased the net photosynthetic rate and r ETR of G.lemaneiformis（P<0.05）.Under HCLT,LP increased Chla content of G.lemaneiformis（P<0.05）.Under LCHT,LP increased the content of PE and PC but decreased the content of SC of G.lemaneiformis（P<0.05）.The results suggested that ocean acidification significantly inhibited G.lemaneiformis growth,but high temperature alleviated the inhibition effect of ocean acidification under P limitation.Under P nutrient sufficiency,the growth significantly increased with temperature increased.3.Two P nutrient gradients(HP:10.1μmol L^-1;LP:0.1μmol L^-1),two salinity gradients（HS:34;LS:25）and two CO₂ concentration levels（HC:1000μatm;LC:400μatm）were set up to study the effects of low salinity,low P nutrient and elevated-CO₂ on the growth and photophysiology of G.lemaneiformis.The results showed that HC had no significant effect on the growth of G.lemaneiformis under HP（P>0.05）,but significantly reduced its growth under LP（P<0.05）.Under LCHP,LS significantly promoted G.lemaneiformis growth.LP decreased the net photosynthetic rate and r ETR under LC（P<0.05）.Under HCLS,LP significantly decreased the content of photosynthetic pigments of G.lemaneiformis（P<0.05）.Under HCHS,LP significantly decreased the contents of SP and SC of G.lemaneiformis（P<0.05）.The results suggested that the interaction of low P nutrient and ocean acidification had negative effects on the growth and photophysiology of G.lemaneiformis.Under LC,the inhibition effect of P limitation on growth under HS was higher than that under LS.However,the inhibition effect was reversed under the ocean acidification condition,that is,the inhibition effect of P limitation on growth under LS was higher than that under HS.