Does the genetic variability of Phragmites australis (Cav.) Trin. ex Steud determine the spatial distribution of the species?

The common reed is a well-known, common and usually dominant species in numerous aquatic and wet ecosystems. It is also a taxon whose representatives live in considerably different habitats. The common reed is capable of adapting to unfavorable habitat conditions. Various ecotypes of the species are characterized by genetic differences, which have enabled the development of mechanisms of resistance to drought, salinity or low temperatures (Chen et al. 2006; Curn et al. 2007; Liu et al. 2012; Rocha et al. 2014). Both the morphology and growth characteristics of the common reed (Phragmites australis (Cav.) Trin. ex Steud) have been studied many times and have provided a great deal of information published in scientific papers (Antonielli et al. 2002; Dykyjová, Hradecká 1976; Engloner 2004; Engloner 2009). The authors of the studies on common reed plants compiled a detailed list of morphological features that should be investigated (Dykyjová et al. 1973). They also presented results proving the negative correlation between the density and the length of shoots (Björk 1967) and the positive correlation between the shoot base diameter and the shoot height as well as between the shoot height and the number of internodes (Ksenofontova 1988; Ostendorp 1991). However, Coops et al. (1996) did not observe a correlation between the common reed shoot base diameter and the shoot length. The most intensive growth of the plant was observed between April and May. After that period, the growth rate gradually decreased until October (Hardej, Ozimek 2002).

The vascular system of plants is responsible for the transport of water as well as dissolved mineral salts, carbohydrates and other nutrients (Chen et al. 2006). So far, researchers have investigated a wide range of characteristics of the vascular structure in plants, e.g. changes in the cell wall architecture, the ionic composition, protein expression and changes in the phloem/wood ratio. According to researchers, all these characteristics contribute to the development of plants’ resistance to stress induced by environmental factors (Child et al. 2003; Equiza, Tognetti 2002; Zwieniecki et al. 2003). Experiments have shown that salinity affects tissue lignification patterns, peroxidase activity and changes in cell wall composition (Wang et al. 1997). Kawashima et al. (2005) observed that plants develop adequate enzymatic properties and gene expression patters in response to environmental changes.

Cell walls have a significant impact on the growth, development and response of plants to environmental factors. They are also responsible for interactions with pathogens and provide signaling molecules that are necessary for self-recognition (Brownlee 2002; Kaczkowski 2003). Differences in the cell wall structure can be the basis for research on plant growth regulation and adaptation to changing environmental conditions (Enstone et al. 2003; Sabba, Lulai 2002). Available studies have shown that modifications of cell wall polymers (lignins, suberins), pectins and proteins in plants growing under stress conditions may result in the formation of barriers to water, gases and pathogens (Hartmann et al. 2002; Hose et al. 2001).

Apart from the common reed morphology and growth characteristics, the influence of environmental factors on the growth of these plants was also researched. Detailed studies on the effect of nutrient availability and soil fertility (Engloner 2009; Hardej, Ozimek 2002; Romero et al. 1999), as well as organic matter decomposition (Van der Putten et al. 1997) and salinity (Lissner et al. 1999) were carried out.

Studies to date have shown that different reed ecotypes growing in different habitats exhibit some regular variability in morphological, physiological and genetic traits in response to salinity and drought (Zhu et al. 2003). So far, the genetic variability of reed clones has been researched using allozyme and molecular marker polymorphism (Clevering, Lissner 1999). The authors of the studies published so far observed the occurrence of large numbers of common reed clones, which could be caused by environmental and genetic factors. Studies have shown that the development of resistance to variable climate, humidity and salinity in P. australis plants is of the genetic nature (Clevering, Lissner 1999).

The main objective of our study was to assess the relationships between the morphology of aerial parts of P. australis plants, the chemical composition of soil or bottom sediments and genetic variability represented by selected markers. We have also tried to identify groups of plants homogeneous in terms of habitat requirements and genetic similarity. Our objective was also to answer the question whether habitat conditions can affect the morphological characteristics of plants and the content of chlorophyll in leaves.

Twenty seven samples gave positive products. Primer URP 2 did not discriminate between the isolates. The two other primers discriminated between the DNA of the isolates. This resulted in 15 polymorphisms in total. There were 3–7 polymorphic markers per primer. The largest number of polymorphic markers resulted from the reaction with primer URP 17R. On average, one primer generated six polymorphic bands. Samples 7, 8, 9, 19, 21 and 1; 4, 5 and 11; and 14 and 17 generated identical band patterns in all the primers. One representative was selected from each group and subjected to phylogenetic analysis, which revealed genetic variability. Samples 32, 28, 26 and 20 became isolated into a separate system (Fig. 2).

Figure 2

The research showed that the highest chlorophyll concentration in P. australis leaves was observed in plant tissues collected in urban areas (Table 1). Specimens from urban areas were taller and had larger laminae.

The comparison in Table 2 shows that the concentrations of all analyzed elements contained in the soil collected in urban areas were lower compared to samples collected in rural areas and open landscape. Only the Ca concentration was higher in the soil from urban areas. The higher concentrations of nutrients in soil samples collected in rural areas and open landscape may have been caused by intensive mineral and organic fertilization. When comparing the results in Table 2 with the data on morphological parameters of P. australis, it can be concluded that common reed plants prefer habitats with calcium-rich soil and slightly alkaline pH. The species may be resistant to deficits or low concentrations of the main nutrients, i.e. N-NO₃ and K.

The research has shown that plants collected from dry areas were smaller. They were shorter, the diameters of their shoots were smaller, and their laminae were shorter and narrower. As evidenced by the standard deviation values, specimens collected from dry areas were characterized by the narrowest amplitude of variation in all morphological parameters (Table 3). The highest chlorophyll content was found in leaves of specimens growing on soils with the highest moisture content.

The content of Ca, Na and NaCl in the soil of wet areas, where the largest specimens were found, was higher compared to the soil at other sites. The soil pH at all the sites was similar. The lowest content of potassium was found in wet soils (Table 4).

The model in Fig. 3 shows the relationships between the morphological parameters of reed plants, chemical parameters of soil, the sites where samples were collected and P. australis specimens. The research has shown that larger specimens occur on soils with higher Ca content and soils more contaminated with NaCl compared to other sites (Table 5). The CVA model shows that P. australis plants growing on wet soils were much taller and had wider leaves. We can assume that wetlands in urban areas with moderately NaCl-contaminated soils are optimal habitats for P. australis plants.

Figure 3

The comparison of the data in the CVA model (Fig. 3) and the results of molecular analysis led to the identification of three groups (G1, G2 and G3) of specimens with homogenous genetic codes and habitat requirements. Group 1 consisted of two specimens only – 14 and 24. They preferred a wet habitat located in the urban area, with a higher content of NaCl in soil (Tables 2 and 4). Groups G2 and G3 consisted of specimens preferring rather dry habitats located in rural or open landscape areas, where soils have a high N-NO₃ content.

The research on the growth and development of common reed revealed differences in the morphological structure of plants growing in waters of different depths. However, the results of experiments were often contradictory (Engloner 2004). Some studies have shown that there was no correlation between the height of shoots, the shoot base diameter and the depth of water in which the plants grew (Coops, Van der Velde 1996; Paucã-Comãnescu et al. 1999; Squires, Van der Valk 1992). Dinka (1986) showed statistically significant differences in the stem height between reeds collected in July at depths of 20–50 cm and those collected at depths of 120–150 cm. However, most of these differences became statistically insignificant at the end of the growing season. White& Ganf (2002) found a positive correlation between the shoot length and the depth of standing water ranging from 5 to 65 cm. They also found a negative correlation at sites with variable water level. As evidenced by our study, there is a correlation between the morphological parameters of common reed plants (the height of plants, the width of the lamina) and their ecosystems. Our study has shown the statistically significant correlation between the height of plants and wet or moist soils in urbanized areas. This means that the height of plants depends on the type of their habitat. However, there are no studies on the impact of habitat conditions (urban, industrial or agricultural areas) on morphological parameters and plant growth.

Wilson et al. (2017) studied the effect of Fe and Mg fertilization and their combinations on the growth of P. australis subsp. americanus. A significant effect of Fe fertilizers on the growth of plants and chlorophyll content in their leaves was found. The same effect was not found in the case of Mg fertilization. Referring these results to those presented in our work, we can conclude that analogously we did not find a significant impact of Mg on the growth of P. australis (CVA model) – the angle of inclination between Mg and plant height. Many authors provide information on the content of minerals in soil in relation to the degree of urbanization. Šorša et al. (2018) and Lollar (2005) strongly indicate the alkaline reaction and higher content of Ca and Mg in soils with a high degree of urbanization (soils of urban and industrial areas) compared to agricultural soils. The above correlation is also confirmed by our research, which was presented in the CVA model.

Salinity is a well-known stress factor for P. australis plants as it reduces their growth rate (Rocha et al. 2014). According to available data, there are considerable fluctuations in the tolerance of reeds to salinity. Different tolerance limits in various ecotypes may depend on plants’ adaptive capacity or genetic factors (Brix 1999; Gorai et al. 2007; Rocha et al. 2014). Our research conducted in central Poland confirmed the resistance of P. australis to salinity. Furthermore, the research showed that specimens growing soils with higher NaCl content were larger (the height of plants, the width of the lamina).

Many researchers reported that reed populations growing in wet and moist areas were characterized by lesser genetic variability than those growing in dry areas (Güsewell, Klötzli 2000; Koppitz 1999; Zeidler et al. 1994). Our study confirmed high genetic variability in different ecosystems and resulted in the identification of genetically similar plants growing both in wet and dry areas. There are two hypotheses accounting for the differences in genetic variability between the locations: 1) the superiority of vegetative reproduction in locations where a population may develop from one or a few rhizomes, or 2) high genetic variability at the initial stage of the population development decreases over time due to natural selection and competition (Curn et al. 2007; Neuhaus et al. 1993). There were four common reed ecotypes found in research conducted in China: swamp reed (SR), low-salt meadow reed (LSMR), high-salt meadow reed (HSMR) and dune reed (DR). The research proved that the ecotypes retained changes in their morphological, physiological and genetic features, which they developed in response to drought and salinity (Chen et al. 2006). According to the Chinese scientists, the genes involved in photosynthesis may increase the photosynthetic capacity of leaves exposed to water stress but this is not directly related to the adaptive capacity of plants exposed to water deficit (Wang et al. 1998). Our study confirmed that there was a significantly higher content of chlorophyll b in the leaves of plants collected in urban areas with water deficit caused by high salinity levels compared to the leaves of plants collected in open landscape rural ecosystems.

Our research and analysis confirm the hypothesis to a certain extent. During the study, we identified three groups of plants homogeneous in terms of habitat and genetic factors (CVA model), which constitute 20% of all examined plants. In our opinion, further research is required on a larger population of P. australis in a wider area.