Freshwater lichens on submerged stones and alder roots in the Polish lowland

The article presents the results of the studies of lichens in streams and spring areas of the escarpment zone of Wzniesienia Łódzkie Heights in Central Poland. The boulders, stones and roots of Alnus glutinosa, situated in 3 inundated zones in the streams: submerged zone, fluvial mesic zone and fluvial xeric zone, were examined in the streams. The studies have shown 23 species connected with these streams. Six species of freshwater lichens: Verrucaria aquatilis, V. hydrela, Hydropunctaria rheitrophila, V. margacea, V. praetermissa and V. madida, occupied stones in 3 different zones. Verrucaria aquatilis and Hydropunctaria rheitrophila colonized also secondary substrates – the bark of alder roots incrusted with sand grains and silt.


INTRODUCTION
In Europe studies of epilithic freshwater lichens and their ecology have been carried out for over a hundred years.A pioneering paper indicative of the zonal distribution of lichens by Santesson was published in 1939.The author was the first to notice that not only a substrate has an effect on the structure of aquatic lichen groups, but also the time of thallus flooding (Coste 2010, after Santesson 1939).
The best so far examined water habitats in England have shown that on all of the localities the lichen species are found in the form of series of overlapping streaks connected with the duration and altitude of flooding, which Gilbert (1996) called zones and distinguished 4 of them: 1 -submerged zone, 2 -fluvial mesic zone, 3 -fluvial xeric zone and 4 -fluvial terrestrial zone.At first, these zones were distinguished on the basis of studies of rivers flowing on cretaceous formations and limestones and later they were confirmed in rivers flowing on acid rocks (Gilbert, Giavarini 1997;Hawksworth 2000).Coste (2010), while he was examining freshwater lichens in France distinguished 3 zones: hyper-hydrophilic lichens, meso-hydrophilic lichens and sub-hydrophilic lichens.In Poland, mainly, montane and submontane streams and rivers were examined, however zonal distribution of lichens was rarely distinguished, e.g., the submerged zone and the splash zone (Krzewicka, Galas 2006;Krzewicka 2009).Kiszka (1998) while he was examining lichens in the Czarna Wisełka and Biała Wisełka catchments distinguished 2 zones: the zone of stream bed and the zone of stream banks.In these habitats he noted 73 epilithic taxa, including lichens directly connected with water habitat of streams and spring areas.
Rivers and streams in the lowland differ from montane streams in substrate of their bottom, built mainly of sand and gravel and their banks are most often overgrown by black alder (Alnus glutinosa) and willows (Salix spp.), which are the components of the streamside alder-ash forest.The alder roots growing directly over the river banks are washed by the flowing water, which deposits grains of sand mixed with silt on these tree roots.The bark of alder roots incrusted with grains of sand glued together with silt makes them similar to the rock substrate and, beside the granite stones, it also constitutes the substrate settled by epilithic freshwater lichens.
The paper presents freshwater lichens poorly known or overlooked in the Polish lowlands growing on the rock substrate and on the roots of trees immersed in water.It is an attempt by show their zonal distribution in freshwater habitats exemplified by the streamsides situated in the area of the escarpment zone of Wzniesienia Łódzkie Heights in Central Poland, which is as a whole under legal protection as Wzniesienia Łódzkie Landscape Park.

STUDY AREA
The habitats where freshwater lichens are found are present at the Wzniesienia Łódzkie Landscape Park.The objects of research were spring areas and rivers belonging to the Vistula's catchment area (Kondracki 2000).The studies were carried out in the spring part of the Bzura river and its tributaries: Mrożyca, Grzmiąca and Kamienna, and Moszczenica with a tributary -Młynówka (Fig. 1).These streams are similar in character to upland rivers.The maximum height difference reaches 100 metres in the upper catchment of Moszczenica stream (Moniewski 2004).
The substrate has an influence on these rivers water chemistry.The boulder clay, gravels and moraine sands make a large contribution to building the river beds.The river bed is often stony with numerous boulders.In relation to chemistry the waters were best examined in Młynówka stream (Ziułkiewicz 1999;Walisch 2007;Ziułkiewicz, Żelazna-Wieczorek 2007a, b).In relation to physicochemical properties they correspond to the values of hydrochemical setting of groundwaters.They are freshwaters, of middling hardness ranging from weakly acidic to slightly alkaline (pH 6.46 to 7.47); a reaction based on the contribution of diatoms indicates the alkalinity of water.The hydrochemical values of water are little unstable, they are mineralized to slight degree (0.1-0.5 g/dm 3 ).A certain changeability of the hydrochemical values results from seasonality and surroundings (forest and field springs).The large contribution of the diatoms demanding high saturation of oxygen in water was noted.
The waters of high quality (Ib class) predominate in the majority of the springs, although individual cases of II and III class can also be found (Moniewski 2004).

MATERIAL AND METHODS
The studied material was the lichens growing in freshwater habitats on siliceous boulders and stones lying in the river and stream beds and on the alder roots and bottoms of trunks growing on the streamsides.The studies were carried out from 2004 to 2008 and in 2011 using the point-based method taking 3 submersion zones into consideration (cf.Gilbert, Giavarini 1997;Hawksworth 2000): 1 -submerged zone (zone with stones and tree roots always submerged in water); 2 -fluvial mesic zone (zone often inundated, with stones and tree roots submerged during the rainfall season); 3 -fluvial xeric zone (zone sporadically inundated, with stones and tree roots submerged or splashed water sporadically, for example during long-lasting rainfall season) -see Figure 2.
Physicochemical measurements of Kamienna and Grzmiąca streams were made by Dr. Zbigniew Kaczkowski and the author in September 2011 (Tab.1).The studies were carried out using the float method (Bujakiewicz-Grabowska, Magnuszewski 2002) in the site of the collection of lichens samples.Temperature of water, pH, saturation and oxygen in water were also measured.

RESULTS AND DISCUSSION
The lichen biota in freshwater habitats is formed of 23 species; they are often accompanied by bryophytes and, sporadically, by red alga Hildenbrandia rivularis growing together with Hydropunctaria rheitrophila.The majority of lichens are epilithic species, but there is a significantly smaller participation of epiphytic lichens.The species of Verrucaria genus are particularly numerous in this habitat (Tab.2).
Freshwater lichens are mainly noted in the initial parts of rivers and streams (Fig. 1), which is probably a result of the increase in water pollution in further parts of the river.These waters are weakly-acidic to slightly alkaline (pH 6.46-7.7)and are well saturated with oxygen.(Tab.1; see also Ziułkiewicz, Żelazna-Wieczorek 2007a, b).
Freshwater lichens are very sensitive to changes in their habitats and therefore are considered to be the good biological indicators of water purity (cf.Gilbert, Giavarini 1997;Gilbert 2001;Krzewicka 2006).
In examined streams, rivers and spring areas aquatic and semiaquatic crustose lichens grow on 2 types of substrates -on siliceous granite boulders, stones and pebbles, and on the roots of Alnus glutinosa, often covered with sand grains or gravel and silt in the submerged zone, and on bark at the base of trees.
Verrucaria aquatilis, V. hydrela and Hydropunctaria rheitrophila (Fig. 3), 3 typical freshwater lichens colonize siliceous boulders and stones in submerged, fluvial mesic and fluvial xeric zones (Tab.2).This is frequently observed in the examined streams (Fig. 1).Among the freshwater lichens Verrucaria aquatilis and V. hydrela are treated as pioneer species, which are first to colonize new substrates; later they are accompanied by Hydropunctaria rheitrophila on the vertical surface of rocks (Keller 2005;Krzewicka, Galas 2006;Krzewicka, Hachułka 2008;Thüs, Schultz 2009).These species are tolerant to a wide range of exposure and moderate eutrophic conditions, and silting in fast running streams.Hydropunctaria rheitrophila is sensitive to silting.This one grows associated with red alga Hildenbrandia rivularis in Kamienna stream.In the investigated streams this red alga was earlier noted also by Żelazna-Wieczorek and Ziułkiewicz (2008).
Amphibious Verrucaria madida occurs in submerged zones only, on inundated granite stones in shaded situation of springs area of the Młynówka stream.V. madida from this locality (Fig. 1) was presented as a new species for Polish biota (Krzewicka, Hachułka 2008).
As for Verrucaria praetermissa (Fig. 5) -it grows on small boulders in periodically inundated zone 2., associated with V. funckii and on stones in sporadically inundated (rather by splash water) zone 3. together with Verrucaria aquatilis and Thelidium aquaticum.This species is sensitive to atmospheric conditions as well as to water acidification and restricted to watercourses with pH>5.It is tolerant to silting and eutrophication (Thüs, Schultz 2009).
Furthermore, Verrucaria funckii and V. dolosa (a terrestrial species but also amphibious of small streams) occur only in zone 2. Verrucaria funckii is a characteristic element of permanently submerged communities in clean springs and headwaters, and is sensitive to silting and acidification (Thüs, Schultz 2009).
Bacidina inundata -amphibious by the splash water in shaded places.The species is tolerant to moderate eutrophication but also sensitive to atmospheric acidification (Thüs, Schultz 2009).Porina chlorotica -a terrestrial species on siliceous stone of bridges in shaded and humid places by splash water.Thelidium aquaticum and Verrucaria sublobulata -amphibious in a streams on granite of bridge.According to Thüs and Schultz (2009) V. sublobulata can also rarely grow on roots of alders.
The results of the studies show that the obligatory freshwater crustose lichens reveal in the streams a tendency to move and colonize the secondary substrate, the roots of A. glutinosa growing on the stream banks, in the submerged and seasonally submerged zones.In both zones, the alder roots are occupied by Hydropunctaria rheitrophila (Fig. 4).In 2 nd zone the alder roots are also colonized by V. aquatilis (cf.Tab. 2).
In lowland Poland, freshwater epilithic lichens growing on the roots of trees are known only from the Białowieża National Park (NE Poland) − Verrucaria hydrela, on submerged roots of A. glutinosa in the Orłówka stream (Czyżewska et al. 2001) and from the Wzniesienia Łódzkie Landscape Park (Central Poland) − V. aquatilis in the Młynówka stream (Krzewicka, Hachułka 2008).
According to Thüs and Schultz (2009) vascular plants do not usually compete with lichens for space.Alder (Alnus glutinosa) and willows (Salix spp.) are occasionally colonized by crustose freshwater lichens.In areas where larger boulders are rare, this substrate can be the most important habitat for amphibious lichens (Motiejūnaitė 2003).
Epiphytic growth of freshwater lichens on the roots of vascular plants is more often observed in the Alps (Thüs, Schultz 2009) and in North-Eastern and Eastern Europe (Motiejūnaitė 2003(Motiejūnaitė , 2009;;Pykälä 2006;Motiejūnaitė, Czyżewska 2008) but is a rare phenomenon in most areas of Central Europe (Thüs, Schultz 2009).
Bacidina sulphurella growing on bark at the base of A. glutinosa is associated with Absconditella lignicola (only in 2 nd zone), Arthonia spadicea and Coenogonium pineti (Tab.2).According to Coppins and Aptroot (2009) this taxon is tolerant of urban conditions.

CONCLUSIONS
In springs and in initial parts of streams and rivers of the escarpment zone of Wzniesienia Łódzkie Heights 23 species of lichens were noted (cf.Tab. 2), 6 of them, closely connected with water, epilithic species are on the red list of threatened lichens of Poland (Cieśliński et al. 2006): VU category -Hydropunctaria rheitrophila, Verrucaria aquatilis and V. hydrela, NT category -V.praetermissa, and DD category -Thelidium aquaticum and V. sublobulata (Figs 1,3,4,5,6), which indicate the very poor extent of study of these habitats in lowland Poland.
The distribution of freshwater lichens in examined streams shows patent zonality.The least numerous, consisted of the epilithic, obligatory freshwater crustose lichens is the submerged zone (see Tab. 2).The most abounding in species is fluvial xeric zone, consisted mostly of facultative, epilithic and epiphytic lichens noted not only on the wet substrate.Similar links have also been observed in the rivers of Lithuania (Motiejūnaitė 2003).
The lichens growing in the investigated streams compete with bryophytes (mosses and liverworts) for substrate.Together on boulders in streams and on the stream banks 7 species of bryophytes were noted, the most of them in sporadically inundated zone 3 (see also Tab. 2).The zonal occupying of the substrates probably exists also among the bryophytes.