CO_2浓度对细基江蓠繁枝变型生长和光合特性的影响

Effect of CO_2 on growth and photosynthetic characteristics of Gracilaria tenuistipitata var. liui Zhang et Xia

比较了低CO_2浓度(充无CO_2空气,low CO_2,简称LC)、正常CO_2浓度(充正常空气,normal CO_2,简称NC)、高CO_2浓度(充正常空气+0.2%CO_2,high CO_2,简称HC)3种条件下细基江蓠繁枝变型(Gracilaria tenuistipitata var.liui Zhang et Xia)的特定生长率、光合色素含量、光合放氧速率和叶绿素荧光参数。结果表明:培养6 d后,与NC组相比,LC组细基江蓠繁枝变型特定生长率(SGR)、100μmol·(m^2·s)^(-1)光强净光合放氧速率及PSII最大光量子产率(Fv/Fm)均显著降低(P<0.05);类胡萝卜素含量显著增加(P<0.05);而藻红素、叶绿素a含量、PSII实际光量子产率(Fv/Fo)、快速光响应曲线初始斜率(α)、最大电子传递效率(ETR_(max))及半饱和光强(I_k)均无显著差异(P>0.05)。与NC组相比,HC组细基江蓠繁枝变型的SGR、Fv/Fm及α显著增加(P<0.05),藻红素含量显著下降(P<0.05),而叶绿素a、类胡萝卜素含量、600μmol·(m^2·s)^(-1)光强净光合放氧速率、Fv/Fo、α、ETR_(max)及I_k均无显著差异(P>0.05)。与LC组相比,HC组细基江蓠繁枝变型的100μmol·(m^2·s)^(-1)光强净光合放氧速率、SGR、Fv/Fm、Fv/Fo、α均显著增加(P<0.05),而藻红素、叶绿素a、类胡萝卜素含量却显著下降(P<0.05),600μmol·(m^2·s)^(-1)光强净光合放氧速率、ETR_(max)、I_k无显著变化(P>0.05)。对于细基江蓠繁枝变型,CO_2浓度升高降低了光合色素含量,同时提高了光系统光能转换效率,而对藻体饱和光强下净光合放氧速率的促进作用不显著。但是CO_2浓度升高却仍然可能通过降低无机碳利用的能量消耗及提高营养盐吸收利用而显著促进藻体的生长。比较不同CO_2浓度下细基江蓠繁枝变型生长和光合特性的差异,有助于初步揭示其对大气CO_2浓度变化的响应特征。

The increase of CO2 concentration in the atmosphere can lead to the increase of dissolved CO2 concentration in sea water accordingly. As the inorganic carbon source of photosynthesis for algae, the change of CO2 concentration has important influences on the photosynthesis and growth of algae. Gracilaria tenuistipitata var. liui Zhang et Xia, an economic marine macroalgae used as abalone feed and agar raw material, has been widely farmed in the southeastern coast of China. The special growth rate （SGR）, photosynthetic pigment content, photosynthetic rates and chlorophyll fluorescence parameters （the maximum quantum yield of PSII photochemistry （Fv/Fm）, the effective quantum yield of PSII photochemistry （Fv/ F0） ,the initial slope of the rapid light curves （α）, the maximum electron transport rate （ETR ） and the photosynthetic half saturation light density （Ik ） of Gracilaria tenuistipitata var. liui Zhang et Xia were measured and compared under different CO2 concentrations, to analyze the influence of different CO2 concentrations on the growth and photosynthesis of this alga. The materials, collected from aquaculture ponds in Qionghai were exposed to three CO2 concentration levels： low （pumping in CO2-removed air, LC ） , normal （ pumping in ambient air, NC） and high （ pumping in ambient air ＋ 0.2% CO2, HC）. Three parallels were set at each level. （ 1.00 ±0.01 ） g algal thallus was put in each beaker with 24 h aeration. The cultivation conditions were as follows： the salinity was 20, temperature （25 ± 1 ） ℃, light intensity 100 μmol·（m2·s）-1,the ratio of light period and dark period was 12L： 12D,the cultivation water was prepared with VSE nutrient solution sea water and was changed every two days. The cultivation lasted for 6 days. Then the algal thalli were taken out and dried by plotting paper. The fresh biomasses of the algae before and after the cultivation were weighed to calculate the specific growth rate. The algal thalli in the similar parts were used to determine the content of chlorophyll a, phycoerythrobilin and carotenoid. 0.08 g algal thalli was weighed, cut up into pieces to measure the oxygen evolution rate （i. e. photosynthetic rate）. Other algal thalli were used to measure the chlorophyll fluorescence parameters by Phyto-PAM. Results showed that： when thalli in LC were compared to those in NC, the special growth rate （SGR）, the net photosynthetic rate under 100 μmol·（m2·s）-1 and the maximum quantum yield of PSII photochemistry （Fv/Fm） decreased significantly （P 〈 0.05 ）, while the contents of carotenoid increased markedly （ P 〈 0.05 ）. In contrast, no difference was observed for chlorophyll a, phycoerythrobilin, the effective quantum yield of PSII photochemistry （Fv/F0） , the initial slope of the rapid light curves （α）, the maximum electron transport rate （ETRr, ax ） or the photosynthetic half saturation light density （ Ik ） （ P 〉 0.05 ）. When thalli in HC were compared to those in NC, SGR, Fv/Fm and a increased significantly （ P 〈 0.05 ）, the content of phycoerythrobilin decreased （ P 〈 0.05 ）, while chlorophyll a, carotenoid, the net photosynthetic rate under 600μmol·（m2·s）-1 had no difference （P 〉 0.05 ）. When thalli in HC were compared to LC, SGR, Fv/Fm, Fv/Fo and α increased significantly （P 〈 0. 05 ）, photosynthetic pigments decreased markedly photosynthetic rate under 600 μmol·（m2·s）-1, the maximum electron photosynthetic half saturation intensity showed no difference （P 〉 0. 05 tenuistipitata var. liui Zhang et Xia, high CO2 concentration can reduce the （P 〈 0. 05）, while the net transport rate （ ETRm~ ） or the ）. To sum up, for Gracilaria photosynthetic pigment contents and motivate the conversion efficiency of light energy of photosynthetic system. However, high CO2 concentration does not lead to a significant promotion on net photosynthetic rate under saturation light intensity. Even so, high CO2 concentration may realize the promotion of the growth of Gracilaria tenuistipitata var. liui Zhang et Xia by reducing the energy consumption of inorganic carbon utilization, as well as improving the nutrient utilization. In this study, investigating the growth and photosynthetic characteristics of Gracilaria tenuistipitata var. liui Zhang et Xia under different CO2 concentration levels can help understand the ecophysiological adaptive ability of this alga to potential CO2 concentration changes.