Differences In Carbon Metabolism Between Gametophyte And Sporophyte Of Pyropia Haitanensis And Responses To Light And Ocean Acidification

Pyropia haitanensis is an important economic seaweed in China,which is cultivated in Fujian,Zhejiang,Guangdong and other coastal areas in China.Pyropia absorbed a large amount of inorganic carbon from seawater by carbon concentration mechanism(CCM)and synthesized organic carbon by photosynthesis.Most of the organic carbon were become the main chemical component of algal tissue carbon(algal tissue C).Other organic carbon were released into seawater in the form of particulate organic carbon(POC)and dissolved organic carbon(DOC).In this way,the large-scale cultivation of Pyropia participates in the offshore carbon cycle through carbon metabolism,which has important ecological significance.The sporophytic generation(filamentous conchocelis)and its gametophytic generation(leafy thallus)of Pyropia have great differences in morphology and living habits,and the generational differences in carbon metabolism(CCM and organic carbon release,etc.)have not been thoroughly studied.Moreover climate change leads to changes in the light intensity and pH of seawater,which have significant effects on the growth and metabolism of algae.Therefore,it is necessary to study the effects of light intensity and ocean acidification(OA)on the carbon metabolism and generation differences of P.haitanensis.The results of this study are as follows:(1)Study the generational differences in the CCM and photosynthesis of conchocelis and thalli in response to light intensity.Pyropia were cultured for two days and seven days under three different light intensities(10,50,500 μmol m-2 s-1).In this study,we found that there were differences in the light response between the conchocelis and thalli in terms of photosynthesis.At the high light intensity(500 μmol m-2 s-1),the maximum quantum yield of PS II(Fv/Fm),net photosynthetic oxygen release rate and the specific growth rate(μ)of thalli were 1.86 times,5.48 times and 38.9 times of conchocelis,respectively.The results showed that compared with the conchocelis,the thalli are better adapted to high light and can withstand strong light stress better.In addition,the study found that light intensity can affect the CCM of Pyropia.At the 500μmol m-2 s-1,the maximum photosynthetic rate(Vmax),extracellular carbonic anhydrase(eCA)and total carbonic anhydrase(total CA)of the thalli increased to 5.7 times,2.6 times and 2.4 times at the 10 μmol m-2 s-1,respectively,the strong light increases the affinity of the Pyropia to inorganic carbon.The generation differences in photosynthesis and inorganic carbon utilization are helpful to further understand the life cycle and regulation of Pyropia.This study found that although light did not directly affect the CCM of Pyropia,it could stimulate the absorption and transport of inorganic carbon by increasing photosynthesis.(2)The generation differences of organic carbon release by Pyropia and the responses to light intensities(10,50,500 μmol m-2·s-1)and pH(7.5,8.1)were studied and analyzed.The results showed that,at pH 8.1,the specific growth rate,algal tissue C/N,algal tissue C-Prod.,and DOC-Prod.of thalli were significantly higher than conchocelis.Algal tissue nitrogen(algal tissue N)contents and algal tissue N/P of conchocelis were significantly higher than thalli.It can be seen that there are significant generational differences in carbon budget and growth of Pyropia,and generational differences in the demand for element N.This study showed that light intensity would affect the carbon budget of Pyropia.For conchocelis grown at normal pH,the increase of light significantly inhibited the μ,and increased the DOC-Prod.and POC-Prod.by 78%and 416%,respectively.Besides,for thalli at normal pH,the increase of light significantly increased the μ,algal tissue C content,tissue C/N,tissue C/P,algal tissue carbon-Prod.and DOC-Prod.by 140%,8.3%,39.1%,82%,99%and 33%,respectively.The high light reduced the algal tissue carbon-Prod.of conchocelis by 92.5%.The high light significantly reduced the algal tissue N content of thalli by 22.4%.Another important environmental factor,OA,significantly increased the algal tissue phosphorus(algal tissue P)content of conchocelis.OA significantly increased the algal tissue C-Prod.of thalli.OA significantly reduced the tissue C/N of thalli.OA significantly reduced the algal tissue C content,tissue C/P,tissue N/P,algal tissue C-Prod.and POC-Prod.of the conchocelis.Moreover,OA interacted with light intensity and affect the algal tissue C-Prod.of thalli and algal tissues N contents of conchocelis.Therefore,as important environmental factors,light intensity and OA may affect the ecological environmental effects of large-scale cultivated Pyropia.From the perspective of carbon metabolism,this study comprehensively analyzed the generation differences between conchocelis and thalli,and the correspondence to light intensity and OA.In combination with the previous results of our team,it shows that there are significant generational differences in inorganic carbon absorption,photosynthetic carbon sequestration and organic carbon release between the conchocelis and thalli.The light intensity and OA had significant effects on the carbon metabolism of Pyropia.Because DOC-Prod.was pretty faster than POC-Prod.of Pyropia,thalli biomass was far higher than that of conchocelis,and increase the light intensity significantly improved DOC-Prod.of thalli,but the OA did not shown significant effect on DOC-Prod.of thalli,we propose that the increase of surface light intensity caused by climate change will greatly improve DOC-Prod.of Pyropia,its ecological environment effect needs further research.This study is helpful to understanding of the differences of carbon metabolism in different generations of Pyropia,and it can be used as a basis for evaluating the effects of OA and light intensity on Pyropia cultivation and cultivation ecology.