Negative and positive aspects of the presence of Canadian goldenrod in the environment

Anthropogenic transformations of the environment in the last few decades have resulted in ecological problems, including invasions of alien plant species. Invasive plant species are entering new territories in great numbers. Their presence is most often the result of conscious or accidental human transfer of diaspores [Tokarska-Guzik et al. 2012]. The greater the human activity and the related transformations of the natural environment are, the more invasive species appear in ecosystems [Chytry et al. 2009]. Successful invasions of plants depend not only on the plants’ biological features and their life strategies but also on the environmental characteristics of the invaded areas and the biological interactions with native organisms [Ehrenfeld 2010; Lanta, Norrdahl 2018]. Invasive plants are most often characterised by rapid growth and intensive reproduction. Their diaspores can be transported over long distances [Myers et al. 2004; Moravcová et al. 2010].

Invasive plants can strongly modify the properties of an ecosystem they inhabit [Eppinga, Molofsky 2013; Sardans et al. 2017]. The degree of ecosystem modification under the influence of invasive plants depends on the species and the place. The high competitive ability of many invasive species reduces the biodiversity of native phytocoenoses [Gioria, Osborne 2014]. Invasive plants can also contribute to soil degradation, which is greater in habitats with low nutrient abundance than in environments richer in nutrients [Sardens et al. 2017].

Numerous studies on the impact of invasive plant species focus on the negative impact of alien plants on native phytocoenoses [Tokarska-Guzik et al. 2012] (e.g. threatening biodiversity and functioning of ecosystems). Positive effects of the presence of invasive alien plants are rarely noted. This paper, based on the literature data and on our own research, discusses both the negative and positive aspects of the occurrence of Canadian goldenrod.

Canadian goldenrod, like the late goldenrod (Solidago gigantea Aiton) and the narrow-leaved goldenrod (Solidago graminifolia (L.) Elliott), is considered an invasive domestic species in Poland [Tokarka-Guzik et al. 2012]. These species represent the genus Solidago spp. (Asteraceae). Most species of goldenrod come from North America [Weber, Schmid 1998]. In the last century, species representing the genus Solidago have spread throughout almost all of Europe [Weber 2000] and Asia [Weber et al. 2008; Semple, Rao 2017]. They are also recorded in Africa [Cheek, Semple 2016] and Australia [Semple, Uesugi 2017; Semple et al. 2017]. They occupy increasingly larger areas in newly invaded habitats [Weber, Schmidt 1998; Tokarska-Guzik et al. 2012].

Among the species of goldenrod occurring in Poland, Canadian goldenrod Solidago canadensis, which was first noted in 1872 [Tokarska-Guzik et al. 2012], deserves special attention. S. canadensis is a perennial plant with a high reproductive ability. The species reproduces generatively and vegetatively [Weber 2000]. Individual shoots produce more than 10,000 seeds, which are easily blown by the wind over long distances. This facilitates the colonisation of new areas at distances far from the parent population [Gassman, Weber 2005]. In new habitats, Solidago usually reaches a greater biomass of the aboveground parts than native species [Zhang et al. 2009]. Goldenrod is a species that penetrates into not only natural [Tokarska-Guzik et al. 2012] and semi-natural (partially transformed) communities but also into plant communities growing in anthropogenic habitats. S. canadensis has a high seed germination rate; under favourable conditions, it reaches the value of 80% [Szymura 2012]. The species is also characterised by a great ability to spread its underground parts: roots and rhizomes. The roots extend to the base of the ramet and reach a minimum depth of 20 cm. Each rhizome can produce a single aboveground stem [Weber 2000]. Individual clones form dense clusters composed of many ramets, depending on the age of the clone. Therefore, in places of its occurrence, especially in anthropogenic habitats, Canadian goldenrod forms extensive and compact fields [Szymura, Wolski 2006]. S. canadensis is characterised by high tolerance to chemical changes in the substrate [Mei et al. 2006; Huang et al. 2007; Priede 2008], such as changes in soil pH, minerals and organic matter. It prefers moist habitats in river valleys, forests, shrubs and meadows [Dajdok, Pawlaczyk 2009]. It also grows massively in fields excluded from agricultural cultivation [Rola, Rola 2010]. It occurs on roadsides, on embankments [Dajdok, Pawlaczyk 2009] and in balks [Szymura, Wolski 2006]. It also overgrows green belts in cities [Guo, Fang 2003]. The species tolerates high levels of metals in the soil [Yang et al. 2008; Nowińska et al. 2012], as evidenced by the presence of the plant in sites near pollutants [Rostański 1997], industrial waste dumps [Rostański 2006], post-industrial wastelands [Antonijević et al. 2012; Nowińska et al. 2012; Patrzałek et al. 2012] and municipal waste landfills [Dyguś 2013]. According to Wang et al. (2021), an important factor in the success of S. canadensis invasion may be its larger height compared to native species, which can enable it to obtain greater competitiveness for sunlight acquisition.

A wide spectrum of habitat conditions, ease of reproduction and entering new areas, and the high competitive ability of S. canadensis lead to its domination in the structures of plant communities. This species has allelopathic effects on co-occurring species. It produces secondary metabolites that are released into the environment by roots and rhizomes and may be the reason for the success of the plant's invasion [Sun et al. 2006; Abhilasha et al. 2008; Yuan et al. 2013]. In places dominated by S. canadensis, reduction in plant species diversity can be as high as 60% [de Groot et al. 2007]. This is especially true of annual species and perennials [Bielecka et al. 2020]. The invasion of goldenrod as a species alien to the native flora is favoured by external factors, such as fragmentation of ecosystems and abandonment of arable land cultivation, as well as modification or degradation of habitats.

The presence of goldenrod, mainly before the flowering period, adversely affects the abundance of insect communities, including wild bees, hoverflies, moths and some ground beetles [de Groot et al. 2007; Moroń et al. 2009; Fenesi et al. 2015]. Insect species, which are narrow food specialists, are particularly exposed to the presence of invasive plant species such as goldenrod [de Groot et al. 2007]. Goldenrod reduces the size of the ant colonies but increases the range of foraging ants; in the goldenrod habitat, worker ants travel greater distances from their mother colony in search of food [Lenda et al. 2013]. In the habitats occupied by goldenrod, there is a decrease in the diversity of bird species and the number of breeding pairs associated with meadow habitats [Skórka et al. 2010]. These changes especially affect insectivorous birds [Tryjanowski et al. 2011].

Invasive plant species can also modify the C and N cycles in the soil [Ehrenfeld 2010]. The presence of goldenrod causes an increase in the organic carbon content in the soil, but it does not significantly affect the nitrogen content. As a result, it causes an increase in the soil's C/N ratio compared to the control sites [Vanderhoeven et al. 2006; Bielecka et al. 2020]; an increase in the C/N value in the soil is one of the symptoms of soil degradation [Baran, Turski 1996].

The presence of S. canadensis in the environment may contribute to the formation of new taxa; in Europe, the formation of the Solidago × Niederederi hybrid, which arises from the crossing of goldenrod S. canadensis with goldenrod S. virgaurea, has been reported. It occurs in anthropogenic habitats together with both parental species, and its presence attests to the invasive character of S. canadensis [Pliszko, Zalewska-Gałosz 2016].

S. canadensis is considered a species that is not easy to control chemically, as shown by its resistance to some herbicides (e.g., Glean 75 WG, Fernando 225EC, Aminopielik D 450 SL). The above-mentioned herbicides used during the growth of S. canadensis (12–14 leaf phase) caused a loss of several percent in the fresh weight of the aboveground parts of the plant. The use of Roundup Ultra 360 SL reduced the fresh mass of the plant by about 60% [Rzymowska et al. 2015]. Similar results were obtained in China, where plant regrowth was also observed after the application of herbicides containing glyphosate, bentazone and oxyfluorfen [Shen et al. 2005].

The high tolerance of S. canadensis to soil contaminated with heavy metals and the accumulation of selected metals in the aboveground and underground parts of the plant can be used in the phytoremediation of contaminated soils. In polluted soils, the plant shows a particular tendency to accumulate Pb [Yang et al. 2008; Xiang et al. 2010; Antonijević et al. 2012; Bielecka, Królak 2019a], Cd [Dąbrowska et al. 2017], Hg [Tomiyasu et al. 2005] and Cu [Antonijević et al. 2012; Bielecka, Królak 2019b] in its underground parts. Research carried out in the vicinity of Olkusz, Poland (a region particularly contaminated with Pb and Zn), showed that S. canadensis accumulates, on average, 520 g Pb/ha (maximum about 3,500 g Pb/ha) and about 450 g Zn/ha (max. 2,500 g/ha) in its underground parts [Bielecka, Królak 2019a]. Therefore, it can act as a phytostabiliser for these metals. It is predisposed to the task by an extensive system of underground organs (roots and rhizomes) [Bielecka, Królak 2019c]. In addition, an extensive system of roots and rhizomes allows for the stabilisation of the substrate and protects against erosion. This is especially important in the case of goldenrod presence in landfills abundant in fine-grained fractions rich in heavy metals.

The plant also has a tendency to transform some metals, such as Zn [Dąbrowska et al. 2017; Bielecka, Królak 2019a] and Mn [Antonijević et al. 2012; Bielecka, Królak 2019b], in its aboveground parts. For example, Canadian goldenrod in the Olkusz area accumulates, on average, about 470 g Zn/ha (max. about 3,300 g/ha) in its aboveground parts. For comparison, Zn accumulation in other plant species (Sorghum biocolor, Helianthus annuus, Brassica Juncewa, Medicago sativa, Zea mays) used in phytoremediation of soils contaminated with this metal is 410 g/ha (H. annuus) to 1,410 g/ha (S. biocolor) [Zhuang et al. 2009]. The plant's ability to accumulate selected metals in its aboveground parts (stems, leaves) can be used in phytoextraction processes in contaminated soils. Klimont (2004) and Klimont et al. (2013) indicate the usefulness of goldenrod in the recultivation of soil degraded by industry. For example, the presence of goldenrod with the addition of municipal sewage sludge in areas of sulphur exploitation improves the chemical properties of the substrate and accelerates the biological regeneration processes of degraded areas [Klimont et al. 2013].

The high biomass of the goldenrod's aboveground parts is also noteworthy. With a plant density of about 120 plants/m², it reaches a biomass of 15.9 tonnes of d.m./ha [Ciesielczuk et al. 2014]. The value is comparable to the biomass of other plant species used in phytoremediation, e.g., Miscantus x giganteus (miscanthus) or Sida hermaphrodita (mallow) [Kabała et al. 2010]. An important property of S. canadensis is its high calorific value, estimated at about 19.3 MJ/kg d.m. [Patrzałek et al. 2012]. The calorific value of S. canadensis is comparable to the calorific value of straw, estimated at 13.5—19.0 MJ/kg d.m. [Denisiuk 2009]. Due to the high biomass of the aboveground parts and the high calorific value of goldenrod, the possibility of using the plant for energy purposes is indicated [e.g., Biskupski et al. 2012; Patrzałek et al. 2012].

Studies conducted in the last decade showed that S. canadensis extracts can significantly inhibit the growth of cyanobacteria in surface waters [Huang et al. 2013, 2014]. The authors indicate the use of S. canadensis as an algicide to control Microcystis blooms. Their presence is noted in eutrophic and hypertrophic lakes [Błaszczyk et al. 2010].

The essential oils obtained from S. canadensis can be used to combat some common plant diseases caused by certain phytopathogenic fungi (e.g., Monilinia fructicola, Botrytis cinerea, Aspergillus niger and Penicillium expansum). They also show antibacterial activity against Bacillus megaterium, Clavibacter michiganensis (G+ve), Xanthomonas campestris, Pseudomonas fluorescens and Pseudomonas syringae pv. phaseolicola (G-ve) and therefore can be used in plant protection [Elshafie et al. 2016, 2019]. The essential oils obtained from the leaves of S. canadensis are also toxic to Culex quinquefasciatus and Spodoptera littoralis third-instar larvae and Musca domestica adult females [Benelli et al. 2019].

The goldenrod flowering period (late summer and early autumn) is valuable for some insects. During this period, predatory and parasitic organisms such as hoverflies but also other pollinators (e.g., the honey bee Apis mellifera [Hurej et al. 2012]) feed on S. canadensis pollen and nectar. Jachuła et al. (2019) report that during the flowering period of Solidago, as many as 80% of insects visiting plant inflorescences are the honey bee Apis mellifera. S. canadensis is considered to be one of the most important honey plants in Central Europe. It blooms in the period when the possibility of bees obtaining honey (nectar, pollen) from other species of honey plants is limited [Amtmann 2010]. The mass of S. canadensis inflorescences during the intensive flowering period is over 20% of the biomass of the aboveground parts of the plant [Bielecka and Królak 2019c]. Due to the formation of dense populations and the massive flower exposure, the plant produces large amounts of nectar. It is estimated that under favourable conditions, goldenrod inflorescences in an area of 1 ha can deliver up to 800 kg of honey [Jabłoński et al. 1992], and S. canadensis is characterised by the highest honey yield among plant species [Lipiński 2010]. Among the honeys available in the Polish market, goldenrod honey has the highest antibiotic activity [Kędzia et al. 2014] and the highest content of organic acids [Sowa et al. 2016], the presence of which extends the expiration of honey [Suarez-Luque et al. 2002]. Goldenrod honey has anti-inflammatory, diuretic and choleretic effects. It is used to treat urolithiasis, inflammation of the urinary system, hypertension, edema, disorders in urination and bile secretion [Różański et al. 2016].

Herba Solidaginis, the herb of goldenrod, containing leaves and inflorescences of the plant, has also been used in medicine. The composition of biologically active substances contained in the raw herbal material and the use of Solidago in modern phytotherapy have been described in Kołodziej et al. (2011), Šutovská et al. (2013) and Różański et al. (2016). The authors report that the substances contained in goldenrod help in the treatment of inflammations and infections of the urinary and sexual system, urolithiasis, inflammation and respiratory infections, hypertension, metabolic disorders, diabetes, rheumatic diseases, and metabolic skin diseases. The essential oil extracted from S. canadensis inflorescence contains active compounds with selective activity on gram-positive and gram-negative bacterial and yeast species and interferes with microbial adhesion [Marinas et al. 2020]. Therefore, goldenrod extracts are used in many medicines, and the raw material is a component of various herbal mixtures applied in phytotherapy. Różański et al. (2016) recommend to make infusions of Solidago flowers or leaves. The low accumulation of heavy metals, such as Pb and Zn in the inflorescences, compared to other morphological parts of S. canadensis is noteworthy [Bielecka et al. 2019a]. Metals particularly toxic to a human organism (Pb, Cd, Hg) mainly accumulate in the underground parts of the plant.

Like other invasive species, S. canadensis shows a rapid growth rate in new habitats, reaches a high biomass of its aboveground parts, degrades habitats and poses a threat to biodiversity. Methods ensuring the almost complete elimination of invasive species of goldenrod from the environment have been described by Kopeć and Michalska-Hejduk (2016).

The presence of S. canadensis in the environment should definitely be kept under control. The easiest way to reduce the infestation of goldenrod is by limiting the spread of its seeds. An effective solution may be cutting plants during the intensive flowering period, before the seeds are fully mature. Material obtained in this way can be used in various ways: as a herbal raw material, an energy raw material, a substrate for the extraction of valuable ingredients used in the fight against fungal and bacterial diseases of plants and in the fight against some algae bloom in water reservoirs.