Zygnematophyceae

Poniewozik, Małgorzata, Duangjan, Kritsana, Pekkoh, Jeeraporn & Wołowski, Konrad, 2020, Algae of bromeliad phytotelmata in the Queen Sirikit Botanical Garden, Chiang Mai, Thailand, Phytotaxa 432 (1), pp. 17-37 : 28

Zygnematophyceae

The interesting group of algae that is represented the most often in bromeliad tanks are desmids ( Zygnematophyceae, Streptophyta). Desmids are typical of shallow, nutrient-poor, acidic or slightly acidic environments ( Coesel 1982, Willén 1992, Reynolds et al. 2002). However, it should be mentioned that there were also many desmid species, e.g., Closterium acutum var. variabile , Closterium moniliferum or Cosmarium granatum typical of alkaline and hard water habitats and known particularly from eutrophic waters where occasionally they may cause a bloom ( Gough 1977, Coesel 2007). Generally, they are very good bioindicators of swamps and bogs, not only with respect to their preference for environmental conditions but also with respect to the current ecological condition and stability of the given ecosystem ( Coesel 2001). In our study, the genera Cosmarium , Mougeotia and Staurastrum were present most frequently ( Table 2). It also means that they were a constant component of the studied tanks, especially at the beginning of our study. The taxa found were represented mainly by well known, widespread organisms. These taxa represented well known genera from lakes, ponds, bogs and bromeliad tanks ( Ramos et al. 2011, 2018). Occurrence of desmids associated with tanks of bromeliads was observed in several studies before ( Sophia et al. 2004; Brouard et al. 2011; Carrias et al. 2014; Ramos et al. 2017). Lush growth of desmids was observed by Ramos et al. (2011) in Alcantarea nahoumii (Leme) J.R.Grant plants, with Cosmarium especially species rich. Water pH is reported to be the main factor influencing the growth of desmids in bromeliad habitats ( Sophia et al. 2004). Many desmids prefer acidic or slightly acidic pH, and our results were consistent with the previous reports with desmids present in bromeliads with water pH 5.45 to 6.40 ( Table 1). There were only two cases with pH above 7. In November 2017, a very lush growth of filamentous Mougeotia parvula was observed in all sample sites excluding Neoregelia compacta tanks. Mougeotia species are known to create blooms in acidic waters in Europe and North America ( Schindler et al. 1985, Webster et al. 1992). Based on field observations, some species of Mougeotia can occur in alkaline pH conditions, but under acidic conditions they become conspicuously abundant ( Schindler et al. 1985, Turner et al. 1987, Kinross et al. 1993). In acidified waters, Mougeotia apparently reaches its maximum abundance around pH 5.2–5.3 ( Webster et al. 1992, Fairchild & Sherman 1993). In our study it occurred in a high abundance in acidic or slightly acidic conditions (pH below 7.0). According to Reynolds et al. (2002) Mougeotia species can tolerate light deficiency and are very sensitive to nutrient deficiency (functional group T), the conditions that were found in our bromeliad tanks. Bromeliads are unique plants that can regulate the pH level itself. In the studies by Lopez et al. (2009) pond water poured into purified and washed tanks became acidic after five to six weeks, since it seems to be a perfect habitat for organisms preferring acidic pH. Acidic reaction of water in bromeliad reservoirs may also favour desmids to settling inside due to their adaptation to use free CO 2 as a source of inorganic carbon ( Sophia et al. 2004). For example, some studies suggest the importance of microorganisms in sustaining high carbon dioxide and low oxygen levels in the water, as affected by the photosynthetic activity of algae ( Laessle, 1961).