Effect Of Light Intensity And Inoculation Proportion On The Population Growth Of Botryococcus Braunii

In order to understand the regulation of inoculation proportions on the population growth of microalgae,this research studied on B.braunii 764 and 765 strains,which were considered as potiential resource of biofuel.This paper contained four main experiments:(1) Photosynthetic characters and growth under 7 light intensities(2,6,14,40,80,120μmol·m^-2.s^-1).(2) Growth and nutrient uptake under 2 light intensities and 7 levels of single N,P stresses(N:0,140,350, 700,1050,1400,3500μg·L^-1;P:12,30,60,90,120,300,600μg·L^-1).(3) Growth under 7 inoculation proportions(10A:0B,1A:9B,3A:7B,5A:5B,7A:3B,9A:1B,0A:10B) at 2 light intensities and 2 medium concentrations.(4) Effect of filtrate on themselves and another B.braunii strain were determined with fresh nutients and without fresh nutrients.The results showed:(1) The biomass of B.braunii and light intensities was positive correlated,while, the light suitability and photosynthetic character of B.braunii strains were different.The biomass of B.braunii 764 and 765 under highest light intensity(120μmol·m^-2·s^-1) were 0.70 and 0.63 g·L^-1,which were 6.1 and 4.6 folds compared with that under lowest light intensity(2μmol·m^-2·s^-1).The photosynthetic light saturation points of B.braunii 764 and 765 were 102 and 80μmol·m^-2·s^-1,while the maximum photosynthetic O₂ evolution rate were 233.93 and 201.54 nmol O₂·mg^-1 Chl a·h^-1.(2) Light intensities and N,P nutrients indicated interactive effect on growth of B.braunii.Moreover,the tolerance of B.braunii strains under N,P stresses were different.Under higher light intensity(110μmol·m^-2·s^-1),B.braunii 764 was sensitive to P stress, however,B.braunii 765 was sensitive to N stress.Increase of light intensity had positive influence on the growth of B.braunii under N stress,however,it had passive influence on the growth of B.braunii 764 under P stress.At high light intensity,the average growth rate of B. braunii 764 was much higher than that of B.braunii 765 under N concentration(＞700μg·L^-1), however,the average growth rate of B.braunii 765 was much higher than that of B.braunii 764 under P concentration(＞116.25μg·L^-1).At low light intensity,The average growth rate of B. braunii 765 was much higher than that of B.braunii 764 under N concentration(3500μg·L^-1). (3) Growth of B.braunii under mixed culture could promote the population growth under certain culture condition.Under Chu10 and 110μmol·m^-2·s^-1,OD₆₈₀ of 9A:1B increased 22% and 20%compared with monoculture,while biomass increased 37%and 38%,3A:7B, 5A:5B,7A:3B also had notable stimulative effect.Under 1.5×Chu10 and 60μmol·m^-2·s^-1, OD₆₈₀ of 7A:3B increased 15%and 10%compared with monoculture,while biomass increased 27%and 33%;Under 110μmol·m^-2·s^-1,OD₆₈₀ of 1A:9B increased 23%and 13% compared with monoculture,while biomass increased 40%and 28%,7A:3B also had distinctive stimulative effect.(4) The allelopathic effect was detected between B.braunii strains, growth of receptor was enhanced even at low concentration of filtrate.The stimulative effect of filtrate was evident at early stage,growth of B.braunii 764 was promoted by filtrate of B. braunii 765 at 4%and 8%treatments remarkably.The growth,biomass and N uptake rate under 100%treatment indicated positive effect significantly.Growth under certain inoculation proportions could increase population growth,that is,B.braunii 764 dominanted and cooccurance of B.braunii 765(7A:3B,9A:1B)at suitable culture conditions.