Response Of Photosynthetic Activity Of Large Seaweed To Different Environmental Conditions

Large seaweed is an important primary producer in offshore ecosystems.It plays an important role in the material cycle and energy flow of offshore ecosystems and plays an important role in maintaining ecosystem stability.Large seaweeds can be divided into economics according to their target orientation.The main-oriented truss-type cultured large seaweed and the large-scale seaweed with natural ecologically oriented natural seaweed field.This study attempts to answer the response of large seaweed photosynthetic activity to different environmental conditions from the perspective of physiological ecology.It provides a theoretical basis for the development of high-efficiency breeding strategies for artificially cultured large seaweeds and the matching of algae in natural seaweed field restoration.In order to solve the influence of temperature and illumination on the growth process of kelp from the perspective of physiological ecology,the physiological response mechanism of kelp to temperature and light environment was explored.In this study,based on the determination of kelp growth parameters in cultured seas,kelp holding experiments with four water temperature gradients of 6°C,10°C,14°C and 18°C were set,and they were at 0,25,70,133,230,317,421,582,786?mol·photons/?m²·s?9 photochemical light gradients.The results show that?1?the kelp fluorescence parameters F_v/F_m and F_v/F₀ are the highest at 0.71 and 2.40respectively at 6?water temperature;the F_v/F_m and F_v/F₀ are the smallest at 18°C water temperature,respectively 0.65 And 1.85;?2?the photochemical quenching and non-photochemical quenching values of the kelp reached the maximum at 18°C water temperature,0.92 and 3.29respectively;?3?the light response curve of kelp increased with photosynthetically active radiation?PAR?The trend of increasing first and then decreasing;?4?the maximum leaf length growth rate,leaf width growth rate and dry weight growth rate of sea cultured kelp were 1.34 cm/d,0.33 cm/d and 1.01 g/d,respectively.The results show that the change of dry weight growth rate of kelp is consistent with the change of light response curve under different water temperature conditions.The high temperature inhibits the photosynthetic efficiency of kelp.When the ambient photosynthetic effective radiation is larger than the sample light saturation point?Em?,the relative electron transport rate of kelp decreases.Photosynthesis is inhibited.In order to explore the distribution of large seaweeds in natural seaweed fields on different water depth gradients and the physiological activities of large seaweeds on different water depth gradients,this study studied the large seaweeds in the natural seaweed field from July to September by means of submersible sampling.Qualitative sampling on the water depth gradient,the photosynthetic pigment content and chlorophyll fluorescence were measured on the collected samples,and the results showed that the daily variation of photosynthetically active radiation?PAR?was relatively stable.During the period from 8:00 to 15:00,the average was 724-1007?mol·photons/?m²·s?,the highest point of photosynthetically active radiation appears at 14 o'clock.The underwater photosynthetically active radiation during the tide period is significantly lower than 1 m below the small tide period,and is close to 0?mol·photons/?m²·s?at 3 m.The general distribution of 10 kinds of large seaweeds on the water depth gradient shows that the water depth is 1m and 2m,the algae species are rich,and the common algae species below 3.5m are less.The leaf-shaped seaweed represented by Dendrobium and Geophyte has more than 1m at low tide,can be exposed to sunlight and maintain its activity for a period of time after ebb,and there are fewer seaweeds at 3.5 m,mainly ponytail.Algae and copper algae.Photosynthetic pigment analysis of Dendrobium at different water depths Dendrobium at depths of 1 m,2 m and 3.5 m did not show significant differences in chlorophyll a,chlorophyll b and carotenoids.The content of photosynthetic pigments of nine large seaweeds collected from seaweed field was analyzed.The content of chlorophyll a in leaf content showed leaf-like>branch-like shape>cylindrical shape,and the photosynthetic pigment content of leaf-shaped seaweed,sea-shell and net algae The highest content of chlorophyll a?Chl a?was 1.59,1.26 and 1.78 mg/g,and the content of chlorophyll b?Chl b?was 0.57,0.48 and 0.63 mg/g,respectively.Carotenoid?Car?content was respectively It was 0.38,0.29 and 0.36 mg/g.The photosynthetic pigment content of coral algae was the lowest,and the three photosynthetic pigment contents were 0.48,0.16 and 0.11 mg/g,respectively.Among the three categories,the non-photochemical quenching index of the three algae of red algae was lower,and the non-photochemical quenching index of three algae of green algae and brown algae was equivalent.With the enhancement of photosynthetically active radiation,the relative electron transport rate of large seaweeds generally increased first and then decreased,while each large seaweed had different adaptability to light,and its semi-saturated light intensity and light saturation point were also different.The relative electron transfer rate shows the trend of Chlorophyta>Brown algae>Red algae gate as a whole.Among the nine large seaweeds,the light energy utilization efficiency of Sargasso,Cucumber,and Cladophora was the highest,0.34,0.35,and 0.32,respectively.The light energy utilization efficiency of coral algae and D.chinensis was the lowest,both were 0.15.The semi-saturated light intensity of coralline algae is the smallest?20?mol·photons/?m²·s??,and the semi-saturated light intensity of the leaf algae is the largest?122.56?mol·photons/?m²·s??.There is no obvious light saturation point between Cladophora and Melissa.From the largest to the smallest,the light saturation interval is Cladophora>M.sylvestris>D.sylvestris>Dendrobium>Copper algae>Sargasso>Coral algae>Net algae>P.The results show that the light adaptability of different algae species determines the location of their living space,and photosynthetically active radiation is the key factor for the distribution of large seaweed on the water depth gradient.