Abstract:

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.

Key words: photosynthetic characteristics, temperature rise, branch, stolon, Caulerpa lentillifera