不同光强下长茎葡萄蕨藻(Caulerpa lentillifera)直立枝和匍匐枝的光生理特征及其对升温的响应

海洋绿藻长茎葡萄蕨藻(Caulerpa lentillifera, 又名海葡萄)因具有较高经济和生态价值而备受关注, 光照和温度变化均会改变长茎葡萄蕨藻生理代谢, 最终影响其经济价值和生态功能。文章比较研究不同生长光强下(40、80、120和160 µmol·photons·m^-2·s^-1)长茎葡萄蕨藻不同部位, 即直立枝和匍匐枝的生理和生化特征, 以及其对升温(+3℃、+6℃和+9℃)的响应。结果显示, 光强由40升至120µmol·photons·m^-2·s^-1时对长茎葡萄蕨藻相对生长率(RGR)的影响不显著, 但是光强升至160µmol·photons·m^-2·s^-1时可使RGR降低49%。弱光下(40µmol·photons·m^-2·s^-1)直立枝的叶绿素(Chl a)和类胡萝卜素(Car)含量为匍匐枝的1.52和1.49倍; 直立枝的Chl a和Car含量随生长光强升高而降低, 匍匐枝随光强升高而升高, 二者蛋白含量则均随光强升高而先升高后降低。弱光下直立枝的净光合放氧速率(P_n)和呼吸速率(R_d)分别为匍匐枝的2倍和70%, 但是二者的最大光化学效率(F_V/F_M)差异不显著。光强升高提高直立枝和匍匐枝的P_n和R_d, 但对二者F_V/F_M的影响不显著。同时, 弱光下直立枝的超氧化物歧化酶(SOD)活性比匍匐枝低20%, 二者过氧化氢酶(CAT)活性差异不显著; 光强升高提高直立枝和匍匐枝的SOD活性, 降低CAT活性。研究还发现, 直立枝和匍匐枝的P_n随温度升高而降低, 但前者的降低程度即光合速率随升温的变化率随光强升高而降低, 后者的则随光强升高而升高, 可见温度升高在弱光下对长茎葡萄蕨藻直立枝的负面影响更大, 在强光下则对匍匐枝的负面影响更大。

Photophysiological characteristics of the branch and stolon of macroalga Caulerpa lentillifera (Caulerpaceae,Caulerpa) under different growth light conditions,and their responses to temperature rise

Marine green macroalga Caulerpa lentillifera (Caulerpaceae, Caulerpa) has attracted significant attention because of its high economic and ecological values. Changes in light and temperature influence the algal physiological metabolism and consequently affect its economic value and ecological function. In this study, biochemical compositions and physiological characteristics of the branch and stolon of C. lentillifera were comparably explored under light intensities of 40, 80, 120 and 160 µmol·photons·m^-2·s^-1, as well as their photosynthetic responses to temperature rise (+3, +6 and +9 ℃) under each light level. The results showed that varying light intensities from 40 to 120 µmol·photons·m^-2·s^-1 had no significant effect on the relative growth rate i.e., RGR, (7.85 ± 0.26) %·d^-1], but the growth light of 160 µmol·photons·m^-2·s^-1 reduced the RGR by 49 %. Under 40 µmol·photons·m^-2·s^-1 light intensity, chlorophyll a (Chl a) and carotenoids (Car) concentrations of branch were (0.15 ± 0.04) and (0.093 ± 0.020) mg·g^-1, being about 1.52- and 1.49-fold of stolon; both Chl a and Car of branch increased with increasing light intensities, but that of stolon decreased. Protein contents of both branch and stolon increased from low to medium growth lights, then decreased to high light, with the maximum values of (1.03 ± 0.00) and (0.95 ± 0.06) mg·g^-1 under 120 µmol·photons·m^-2·s^-1, respectively. Under 40 µmol·photons·m^-2·s^-1 light intensity, the photosynthetic oxygen evolution rate (P_n), dark respiration rate (R_d) and photosynthetic efficiency (F_V/F_M) of branch were (3.10 ± 0.71), (2.14 ± 0.09) µmol·g^-1·h^-1 and (0.74 ± 0.04), wherein the P_n and R_d were 2-fold and 70 % of stolon, but no significant difference in the F_V/F_M between them. Both P_n and Rd increased with rising growth lights, but the F_V/F_M did not change. Superoxide dismutase (SOD) activity in branch (11.0 ± 1.32) U·g^-1] was about 20 % lower than that in stolon under 40 µmol·photons·m^-2·s^-1 growth light, while the catalase (CAT) activity (3.80 ± 0.21) U·g^-1] was similar. The SOD activity increased with increasing growth lights in both branch and stolon, but the CAT activity decreased. Particularly, our results demonstrated that the temperature rise reduced the P_n of both branch and stolon, with the reduction degree (i.e., the slope of P_n versus temperature) decreased with growth lights in branch, but increased in stolon, indicating the temperature rise maybe more harmful to branch in low light and to stolon in high light conditions.