DNA DAMAGE AND PHOTOSYNTHETIC PERFORMANCE IN THE ANTARCTIC TERRESTRIAL ALGA PRASIOLA CRISPA SSP. ANTARCTICA (CHLOROPHYTA) UNDER MANIPULATED UV-B RADIATION

The effect of reduced, natural ambient, and enhanced UV-B radiation (UVBR) on photosynthesis and DNA damage in the Antarctic terrestrial alga Prasiola crispa ssp. antarctica (Kützing) Knebel was investigated in two field experiments. Samples of P. crispa were collected underneath snow cover and exposed outside to reduced and natural UVBR in the austral spring. In a second experiment at the end of the austral summer, samples were exposed to ambient and enhanced UVBR. PSII efficiency, net photosynthetic rate (NP), dark respiration rate (DR), UV-absorbing pigments, and cyclobutyl pyrimidine dimer (CPD) formation were measured during the experiments. In October 1998, a spring midday maximum of 2.0 W·m ^{− 2} of UVBR did not significantly affect effective quantum yield (ΔF/F_m′), and a reduction in the ratio of variable to maximal fluorescence (F_v/F_m) in the late afternoon was transient. Exposure to natural ambient UVBR in October increased CPD values significantly. Midday maxima of UVBR during the experiments in October and January were comparable, but Setlow-DNA-weighted UVBR was more than 50% lower in January than in October. In January, 0.5 W·m ^{− 2} additional UVBR during 10 h did not have a negative effect on ΔF/F_m′. The reduction in F_v/F_m was not significant. NP and DR were not affected by supplementation of UVBR. Although photosynthetic activity remained largely unaffected by UVBR treatment, DNA damage was shown to be a sensitive parameter to monitor UVBR effects. Supplementation of additional UVBR did significantly enhance the amounts of CPD in exposed samples and repair took place overnight. It is concluded that PSII and whole-chain photosynthesis of P. crispa is well adapted to ambient and enhanced levels of UVBR but that CPD formation is more sensitive to UVBR than to photosynthesis.     

Consequences of depletion of stratospheric ozone for terrestrial Antarctic ecosystems: the response of Deschampsia antarctica to enhanced UV-B radiation in a controlled environment

Mini UV lamps were installed over antarctic plants at Léonie Island, Antarctic peninsula, and shoot length measurements of Deschampsia antarctica were performed during the austral summer January–February 1999.We studied the response of the antarctic hairgrass, Deschampsia antarctica to enhanced UV-B. In a climate room experiment we exposed tillers of Deschampsia antarctica, collected at Léonie Island, Antarctic peninsula, to ambient and enhanced levels of UV-B radiation. In this climate room experiment with 0, 2.5 and 5 kJ m^–2 day^–1 UV-B_BE treatments we observed that length growth of shoots at 2.5 and 5 kJ m^–2 day^–1 UV-B_BE was markedly reduced compared to 0 kJ m^–2 day^–1 UV-B_BE. In addition, there was an increased number of shoots and increased leaf thickness with enhanced UV-B. The Relative Growth Rate (RGR) was not affected by UV-B, possibly because reduced shoot length growth by enhanced UV-B was compensated by increased tillering. Light response curves of net leaf photosynthesis of plants exposed to 5 kJ m^–2 day^–1 UV-B_BE did not differ from those exposed to 0 kJ m^–2 day^–1 UV-B_BE. The content of UV-B absorbing compounds of plants exposed to increasing UV-B did not significantly change.Mini UV-B lamp systems were installed in the field, to expose the terrestrial antarctic vegetation at Léonie Island to enhanced solar UV-B. In that study, the increment of shoot length of tagged plants of Deschampsia antarctica during the January-February 1999 at Léonie Island, was recorded and compared to shoot length growth under controlled conditions.The consequences of enhanced UV-B radiation as a result of ozone depletion for the terrestrial antarctic ecosytems are discussed.     

The effects of altered levels of UV-B radiation on an Antarctic grass and lichen

We report a long-term experiment on the photosynthetic response of natural vegetation of Deschampsia antarctica (Poaceae) and Turgidosculum complicatulum (Lichenes) to altered UV-B levels on Léonie Island, Antarctica.UV-B above the vegetation was reduced by filter screens during two seasons. Half of the screens were transparent to UV-A and UV-B (ambient treatment) or absorbing UV-B and part of the UV-A (below-ambient treatment). Half of the wedge- shaped filters had side walls leading to an enhancement of the daily mean temperature in summer by 2–4 °C, simulating rising mean air temperature on the Antarctic Peninsula. The other half of the filters were without side walls resulting in close-to-ambient temperature underneath. Plots without filters served as controls.UV-B supplementation of an extra 1.3 kJ UV-B_BE was achieved using UV-mini-lamp systems during 15 days in the second season.We found no evidence that altered incident UV-B levels and temperature had an effect on maximum photosystem II efficiency (F _v/F _m) and effective photosystem II efficiency (F/F _m) in both species. UV-B reduction did not influence contents of chlorophyll, carotenoids and methanol-soluble UV absorbing compounds in D. antarctica.Flowering shoot length of D. antarctica was not affected by UV-B reduction. Temperature enhancement tended to result in longer inflorescence axes. Results of two austral summer seasons of UV- reduction in natural stands of D. antarctica and T. complicatulum suggest that current ambient levels of UV-B do not have a direct effect on the photosynthetic performance and pigment contents of these species. Cumulative effects on growth have not been recorded after two years but can not be excluded on a longer term.     

Effect of pH on Rhodomonas salina growth,biochemical composition,and taste,produced in semi-large scale under sunlight conditions

Journal of Applied Phycology - Rhodomonas salina is a microalgal species, belonging to the cryptophytes, and is widely used as aquaculture feed because of its high nutritional profile and...