Effects Of Environmental Changes On Photosynthetic Activity Of Macroalgae In Different Phyla And Life Stages

Macroalgae are an important contributor to the ocean’s blue carbon sink,and their photosynthesis also provides 90 percent of the energy for life on Earth.However,growing in the sensitive intertidal zone,the photosynthetic activity of macroalgae is affected by various environments.Macroalgae have three classes and several life stages.Complex environmental changes have different effects on the photosynthetic activity of macroalgae in different classes or life stages.In this study,all research angles of the measurement of photosynthetic activity of macroalgae were integrated,and representative parameters from each Angle were selected as the indicators for the analysis of photosynthetic activity,so as to conduct a more scientific,complete and credible analysis of the results of photosynthetic activity.(1)In order to explore the different effects of environmental changes on the photosynthetic activity of macroalgae of different categories,this study selected the typical species of the three categories of macroalgae,Ulva lactuca(Chlorophyta),Sargassum horueri(Phaeophyta),and Hypnea boergesenii(Rhodophyta).The main environmental factors,temperature and light intensity,were selected as variables,and the indoor culture of macroalgae was carried out through the orthogonal design of two factors and three levels.Various photosynthetic activity parameters were determined.Main results: The effects of temperature and light intensity on the photosynthetic activity of different species of macroalgae were different.For macroalgae growing in shallow water layer,temperature change has a greater effect on growth and pigment content.The pigment content of macroalgae in deep water layer is more likely to be affected by the change of light intensity,and its energy transfer and conversion efficiency is more likely to be affected by the change of temperature.Seaweed has low light adaptability.Reducing light intensity is not conducive to promoting growth,but conducive to pigment accumulation and promoting more energy allocation for photosynthesis.The increase of temperature can promote the energy transfer and transformation of seaweed in deep water.(2)In order to explore the influence of complex coupling effects of environmental factors on the photosynthetic activity of macroalgae,this study selected Sargassum horueri,a typical algae species,and selected the main environmental factors light intensity,inorganic nitrogen and inorganic phosphorus elements as variables.Through the orthogonal design of three factors and three levels,indoor culture of macroalgae was carried out,and a variety of photosynthetic activity parameters were determined.Main results: Both light and nutrients had significant effects on the growth and photosynthetic activity of Sargassum horueri from different sides,and the effect of light intensity was more obvious than that of nitrogen and phosphorus nutrients.With the increase of inorganic nitrogen concentration,the growth rate and maximum potential relative electron transport rate of Sargassum horueri firstly increased and then decreased,and the growth rate and photosynthetic activity of Sargassum horueri were the highest under the medium nitrogen(N2)level.Medium phosphorus(P2)is conducive to the accumulation of photosynthetic pigments.The enhancement of light can inhibit the growth of Sargassum horueri and the energy transfer and transformation in the photosystem.Therefore,on the basis of site environmental conditions,reducing light intensity is not conducive to the growth of macroalgae,but will promote photosynthesis.Increasing temperature was more conducive to photosynthesis of algae in deep water layer.Moderate reduction of light intensity and increase of nitrogen and phosphorus nutrient concentration were beneficial to promote the growth and photosynthetic activity of Sargassum horueri.(3)In order to explore the comparison of the effects of environmental coupling on the photosynthetic activity of macroalgae at different life stages,this study selected Sargassum horueri,a typical algae species,and selected the main environmental factors temperature and light intensity as variables.Through the orthogonal design of two factors and three levels,the indoor culture of macroalgae was carried out,and a variety of photosynthetic activity parameters were determined.Main results: The sensitivity of photosynthetic activity to temperature and light intensity was different in the two key growth stages: seedling stage and algal stage.The growth of seedling stage was more sensitive to temperature change,the growth of algal stage was more sensitive to light intensity change,and the situation of pigment content was opposite to growth.Therefore,the growth rate of Sargassum horueri can be controlled by changing the temperature during the seedling stage.During the algal stage,the growth rate is controlled by changing the light intensity.For Sargassum horueri at key growth stages,the light intensity can be reduced appropriately to promote growth,photosynthetic pigment accumulation and low light utilization,and improve photosynthetic activity.Appropriately increasing temperature promoted low light utilization and photosynthetic activity of Sargassum horueri.A more stable culture environment is needed to maintain normal growth and photosynthesis of Sargassum horueri in the seedling stage.In summary,this paper conducted indoor culture of macroalgae through orthogonal design to compare the effects of environmental changes on photosynthetic activity of macroalgae of different phyla.The effects of complex coupled environment on photosynthetic activity of Sargassum horueri and the comparison of environmental changes on photosynthetic activity of Sargassum horueri at different life stages were investigated.This study provides scientific basis for the physiological and ecological research on the stress response of environmental factors and photosynthetic activity of macroalgae.Clarifying these influencing factors and their joint action will be of great significance for the selection of algae species for ecological restoration in seaweed field,the cultivation technology of macroalgae artificial culture and the evaluation of the effect of algae carbon sequestration.