Effect of solar UV‐B exclusion on the phytoplankton community in a sub‐tropical mountain reservoir: a mesocosm study

Abstract

A mesocosm experiment was conducted over a 4 week period to investigate the response of a phytoplankton community in a mountain freshwater reservoir to solar UV-B exclusion. The mesocosms were filled with water taken from the depth of 0.30 m in the reservoir, and exposed to near-ambient solar UV-B (+UV-B) and solar UV-B exclusion ()UV-B). The resulting chlorophyll-a (Chl-a), carotenoids, soluble sugars, algal composition and algal abundance were analysed. The study results indicated that carotenoids, carbohydrates and species distribution were affected under the )UV-B treatment. The carotenoid concentration was generally higher under the +UV-B treatment than under the )UV-B treatment. The sucrose and glucose concentrations were affected differently by the UV-B treatments, although both sugars strongly decreased under the +UV-B treatment by the end of the experiment. The sucrose and glucose concentrations exhibited similar distribution patterns to those of carotenoids for the +UV-B treatment, suggesting that these sugars could be directly involved in secondary metabolism. In contrast, the fructose content did not exhibit significant differences between UV-B treatments. The Chl-a concentration exhibited a progressive decrease during the experiment for both UV-B treatments. Although no significant impact of UV-B exclusion on the Chl-a concentration was observed in this study, a slightly higher concentration was observed for the )UV-B treatment. The total phytoplankton biovolume (BV) exhibited a pattern similar to that of the Chl-a concentration. Analysis of the phytoplankton composition revealed 52 species. However, because some species and classes were extremely difficult to identify, only 46 species from seven classes (Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae, Charophyceae, Dinophyceae, Xanthophyceae) were unambiguously identified and considered for the UV-B treatments. Chlorophyceae, Bacillariophyceae and Cyanophyceae comprised about 78% of the identified species. Aulacoseira granulata and Cyclotella meneghiniana, followed by Ceratium hirundinella, were the most abundant species. Principal component analysis, using sampling periods and algal densities (PCA-1), indicated a heterogeneous phytoplankton assemblage, whereas PCA-2, with algal densities and biochemical variables (soluble carbohydrates, Chl-a and carotenoids), indicated that biochemical parameters could provide qualitative information about La Angostura phytoplankton community responses to quality of the sunlight.

Photosynthesis of two moss crusts from the Tengger Desert with contrasting sensitivity to supplementary UV-B radiation

“…Loss of Chl is a negative effect of UV-B and may be an indication of ongoing senescence (Weichmann 2000). Many reports have shown that one of the most common symptoms of elevated UV-B exposure is a decrease in Chl concentration (Medina et al 2010, Zu et al 2011. Declines in Chl concentration in UV-B treated shoots have been related to the suppression of aminolevulinic acid synthesis or a reduction in protochlorophyllide (Choi and Roh 2003).…”

Phytoplankton primary production in freshwater environments of Argentina

“…These seasonal variations in k PAR following the annual succession of phytoplankton were also determined in the Lake Cacique Chiquichano (Chubut Province) in the Patagonian Plateau, where k PAR values varied between 0.44 and 12.5 m -1 (Gonçalves et al 2007. Finally, in studies carried out in the Peri-Pampean Sierras (i.e., Lake La Angostura) Helbling et al (2006) determined values of k PAR of 1.7 m -1 during the summer, however, Medina et al (2010) found relatively higher penetration of solar radiation at the same study site, with 83-86% (PAR) of incoming irradiances at 0.30 m. These differences are attributed to the fact that the former study was performed during the rainy season thus higher amounts of terrigenous material were transported to the lake.…”