Zengling Ma

Differential responses of Nostoc sphaeroides and Arthrospira platensis to solar ultraviolet radiation exposure

During October to December 2003 we carried out experiments to assess the impact of high solar radiation levels (as normally occurring in a tropical region of Southern China) on the cyanobacteria Nostoc sphaeroides and Arthrospira (Spirulina) platensis. Two types of experiments were done: a) Short-term (i.e., 20 min) oxygen production of samples exposed to two radiation treatments (i.e., PAR+UVR—280–700 nm, and PAR only—400–700 nm, PAB and P treatments, respectively), and b) Long-term (i.e., 12 days) evaluation of photosynthetic quantum yield (Y) of samples exposed to three radiation treatments (i.e., PAB; PA (PAR+UV-A, 320–700 nm) and P treatments, respectively). N. sphaeroides was resistant to UVR, with no significant differences (P>0.05) in oxygen production within 20 min of exposure, but with a slight inhibition of Y within hours. A fast recovery of Y was observed after one day even in samples exposed to full solar radiation. A. platensis, on the other hand, was very sensitive to solar radiation (mainly to UV-B), as determined by oxygen production and Y measurements. A. platensis had a circadian rhythm of photosynthetic inhibition, and during the first six days of exposure to solar radiation, it varied between 80 and 100% at local noon, but cells recovered significantly during afternoon hours. There was a significant decrease in photosynthetic inhibition after the first week of exposure with values less than 50% at local noon in samples receiving full solar radiation. Samples exposed to PA and P treatments recovered much faster (within 2–3 days), and there were no significant differences in Y between the three radiation treatments when irradiance was low (late afternoon to early morning). Long-term acclimation seems to be important in A. platensis to cope with high UVR levels however, it is not attained through the synthesis of UV-absorbing compounds but it seems to be mostly related to adaptive morphological changes.

Effects of solar ultraviolet radiation on biomass production and pigment contents of Spirulina platensis in commercial operations under sunny and cloudy weather conditions

Shantou Univ, Marine Biol Inst, Shantou 515063, Guangdong, Peoples R China; Chinese Acad Sci, Inst Hydrobiol, Wuhan 430072, Hubei, Peoples R China; Hainan DIC Microalgae Co Ltd, Haikou Int Commercial Ctr, Haikou 570102, Hainan, Peoples R China

Impacts of solar UV radiation on grazing, lipids oxidation and survival of Acartia pacifica Steuer (Copepod)

UV radiation is known to affect aquatic primary producers and their grazers. However, little has been documented on its effects on zooplankton grazing. In this study, the authors investigated the effects of photosynthetically active radiation (PAR, 400–700 nm), ultraviolet-A (UV-A, 320–400 nm) and ultraviolet-B (UV-B, 280–320 nm) radiation on grazing, mortality and lipids oxidation of the copepod Acartia pacifica collected from the Xiamen Bay. After 30 min of the exposures, the copepod was fed in darkness with the diatom Phaeodactylum tricornutum at two cell concentrations (2.5×104 and 2.5×105 cells/ml). At the low cell concentration, the individuals pre-exposed to PAR (218.0 W/m2)+UV-A (48.2 W/m2) or PAR+UV-A+UV-B (2.1 W/m2) showed suppressed clearance and grazing activities compared with those receiving PAR alone, by 22.7% and 17.1% for clearance and by 22.6% and 5.5% for grazing rates, respectively. However, the suppression on clearance and grazing became indistinctive at the high food concentration. Exposures to UV-A and UV-B led to increased lipid oxidation and higher mortality, furthermore, the mortality linearly increased with enhanced oxidation of lipid.

Carbon limitation enhances CO2 concentrating mechanism but reduces trichome size in Arthrospira platensis (cyanobacterium)

Arthrospira species grow well under highly enriched inorganic carbon concentrations, but little is known on the effects of inorganic carbon (Ci) limitation on its physiological performance. When Arthrospira platensis D-0083 was grown in a modified medium without NaHCO3 under ambient air of 380 ppm CO2, its trichomes became disassembled while the growth and photosynthetic rates were severely reduced. Phycocyanin and allophycocyanin contents decreased but the carotenoid content increased under the Ci limitation. Compared with the cells grown in Zarrouk medium, the trichomes grown under the Ci limitation increased their photosynthetic apparent affinity for Ci by about 14 times but photochemical quenching capacity was reduced. It appeared that A. platensis increased its CO2 concentrating mechanism by inducing HCO3− transporters and reducing the trichome size which increased filamentous surface to volume ratio.

Behavioral responses of zooplankton to solar radiation changes: in situ evidence

It is known that copepods can sense solar UV and avoid it vertically or horizontally, but no in situ studies have been documented to monitor their responses to diurnal solar radiation changes. Here, we provided in situ evidence that zooplankton sense changes in solar radiation during a diurnal solar cycle. By comparing the abundance of the zooplankton in a shaded water column with that in the non-shaded adjacent area, we found that, on a cloudy day with low solar radiation levels, the ratios of zooplankton biomass in the shaded areas to those in nearby non-shaded water ranged from 0.90 to 1.49. However, on sunny days with high solar radiation levels, the ratios ranged from 0.83 to 2.88, with the amount of zooplankton in the shaded water being higher than that in the non-shaded area and higher during the periods of higher irradiance levels. These results indicated that the horizontal migration of zooplankton may be a protective strategy against stressful solar radiation.