Study On Physioecological Characteristics And Tissue Culture Of The Brown Alga Sargassum Thunbergii

One-year investigation on physioecological characteristics of the brown algaSargassum thunbergii collected from the intertidal zone along the coast of Taipingjiao,Qingdao, is carried out. Simultaneously, exploitation of rapid propagation techniqueof S. thunbergii is also attempted. Seasonal changes in morphological characteristicsof S. thunbergii and their link with environmental sea water temperature are firstlyrecorded; and seasonal changes in nitrogen uptake by S. thunbergii are examinedunder different temperature levels and nitrogen concentration levels; the effect oftemperature and nitrogen on growth and maturation of S. thunbergii are nextexamined by culture experiments; and finally, exploitation of rapid propagationtechnique of S. thunbergii seedlings is attempted using adventitious buds regeneratedfrom explants of rhizoid.1. Seasonal changes in morphological characteristics of S. thunbergii and theirlink with environmental sea water temperature.The average length of primary branches maintained about3cm from November2010to March2011and almost no seasonal changes were found with decrease of seawater temperature from14℃to3℃. From March to July2011, the average length ofprimary branches increased rapidly with increase of sea water temperature from3℃to20.5℃. Moreover, the formation of pneumathode, lateral branch and receptaclewere observed successively in March, May, and July. The average length of primarybranches （26.62±13.45cm）, the average number of lateral branches in a primarybranch （33.18±24.53individual）, the percentage of primary branches withpneumathodes （69.47±29.24%）, and the percentage of primary branches withreceptacles （70.38±27.90%） reached their maximum values in July. With furtherincrease of sea water temperature from20.5℃in July to24℃in September, the average length of primary branches and the percentage of primary branches withreceptacles decreased to3.35±0.73cm and8.72±0.36%, respectively, and the lateralbranches and pneumathodes disappeared. Based on these results, the annual life cycleof S. thunbergii along the coast of Taipingjiao, Qingdao, can be divided into4stages:slow growth stage （November-March）, rapid growth and pre-maturation stage（May-July）, late-maturation and shedding stage （July-September）, and germinatingstage （September-November）.2. Seasonal changes in nitrogen uptake of S.thunbergiiSeasonal changes in uptake rates of NO₃^--N and NH₄⁺-N by S.thunbergii weremainly examined at different temperature and nitrogen concentration levels. Uptakeexperiments were conducted at5-6temperature levels （10,15,20,24,30,35℃） and5nitrogen concentration levels （1/4PESI,1/8PESI,1/16PESI,1/32PESI, FSW） usingadult and young S.thunbergii sporophytes. Significant differences in NO₃^--N uptakeby adult S.thunbergii were found among seasons and temperatures. The uptake rate ofNO₃^--N was less than20μg/g·w/h in November, followed by an increase to20-60μg/g·w/h from January to May, and then down to less than20μg/g·w/h in Julyand down to less than5μg/g·w/h in September. However, no seasonal changes werefound in NH₄⁺-N uptake rates. Although NO₃^--N and NH₄⁺-N were absorbed at10-30℃, the temperature at which the maximum NO₃^--N and NH₄⁺-N uptake rateswere observed ranged from20℃-24℃from May to July to20℃in otherexperimental seasons. NO₃^--N uptake rates were significantly higher than NH₄⁺-Nuptakes rates from January to May.Significant differences in NO₃^--N uptake by adult S.thunbergii were also foundamong seasons and nitrogen concentrations. The uptake rate of NO₃^--N saturated at1692-3110μg/L from November to January with the maximum rate remaining lessthan35μg/g·w/h. The uptake rate of NO₃^--N did not saturate even at3582-4500μg/Lfrom March to May with the maximum rate up to60-70μg/g·w/h. The uptake rate ofNO₃^--N saturated at851-1419μg/L with the maximum rate down to less than35μg/g·w/h. The uptake rate of NH₄⁺-N did not saturated throughout the year, but the maximum rate remained less than20μg/g·w/h. The uptake rate of NO₃^--N was higherthan that of NH₄⁺-N with the increase of nitrogen concentration from May to July.Significant differences in NO₃^--N and NH₄⁺-N uptake by young sporophytes ofS.thunbergii were found among temperatures and nitrogen concentrations. NO₃^--Nand NH₄⁺-N uptake rate decreased significantly at35℃, although no differences werefound among10-30℃. The maximum rate of NO₃^--N and NH₄⁺-N were observed at15℃and20℃, respectively. The uptake rate of NH₄⁺-N and NO₃^--N saturated at365μg/L and1377μg/L, respectively.3. Effect of temperature and nitrogen on growth of S. thunbergiiThe growth experiments were carried out at5temperature levels （5levels wereselected from5、10、15、20、24、30℃according to the sea water temperature in situin the current month） and2mediums （N-enriched1/4PESI and N-removed ASS₂）using the adult and young sporophytes of S. thunbergii. Seasonal changes in SGRwere observed for both algal fresh wet and algal length. The SGR of algal fresh wetremained less than4%/d from November2010to January2011, increased to3-12%/dfrom March to July, and then decreased to less than4%/d in September. The SGR ofalgal length remained less than7%/d from November2010to January2011, increasedto2-13%/d from March to May, and then decreased to less than4%/d from July toSeptember. Significant differences in SGR were found among temperatures andnitrogen supplies. Positive growth of adult sporophytes in both mediums could beobserved at5-30℃in any month. However, the optimal growth temperatures inN-enriched1/4PESI medium was5-10℃higher than those in N-removed ASS₂medium from May to September, suggesting that nitrogen can promote adultsporophytes against high temperature. The SGRs of algal fresh wet and algal length inN-enriched1/4PESI medium were significantly higher than those in N-removed ASS₂medium from March to July and from March to May, respectively.Significant differences in SGR of young saprophytes were also found amongtemperatures and nitrogen supplies. The SGRs of algal fresh wet and algal length decreased significantly at35℃although they have no differences among15-30℃.The SGRs of algal fresh wet and algal length in N-enriched1/4PESI medium weresignificantly higher than those in N-removed ASS₂medium at any temperature except20℃.4. Rapid propagation technique of S.thunbergii seedlings by tissue cultureThe adventitious buds regenerated from the explants of rhizoids of S. thunbergiiwere obtained as seedlings, and the pr℃ess of growth and development from anadventitious bud to a new plant with receptacles was recorded. Effect of3temperaturelevels （15、20、24℃） and3mediums （PESI, N-removed ASS₂, and FSW） onformation of adventitious buds were compared. FSW was the best, in which thepercentage of explants with adventitious buds was60-80%and the number ofadventitious buds per explants was3-6individuals. Next is N-removed ASS₂, inwhich the percentage of explants with adventitious buds was60-75%and the numberof adventitious buds per explants was2-5individuals. The optimal temperature foradventitious buds formation was20℃. The adventitious buds grew up and developedinto a new plant with receptacles through In vitro culture.