Competition Between Native Antarctic Vascular Plants and Invasive Poa Annua Changes with Temperature and Soil Nitrogen Availability

Biol Invasions (2018) 20:1597–1610 https://doi.org/10.1007/s10530-017-1650-7 ORIGINAL PAPER Competition between native Antarctic vascular plants and invasive Poa annua changes with temperature and soil nitrogen availability Lohengrin A. Cavieres . Ana Karen Sanhueza . Gustavo Torres-Mellado . Ange´lica Casanova-Katny Received: 25 April 2017 / Accepted: 10 December 2017 / Published online: 16 December 2017 Ó Springer International Publishing AG, part of Springer Nature 2017 Abstract Over the last decades human have intro- Individual mats of the study species were collected duced non-native organisms to Antarctica, including in King George Island, and then transported to the grass species Poa annua. This non-native grass Concepcion where we conducted competition exper- under constant growth temperatures has been shown iments. In the first experiment we used soil similar to negatively affect the growth of the only two native that of Antarctica and plants in competition were Antarctic vascular plants, Deschampsia antarctica grown at two temperatures: 5°/2° and 11°/5 °C (day/ and Colobanthus quitensis, under constant growth night temperature). In a second experiment plants temperatures. However, whether there are changes in were grown in these two temperature regimes, but we the interaction between these species under warmer varied nitrogen (N) availability by irrigating plants conditions is an important question. In cold ecosys- with Hoagland solutions that contained 8000 or tems, soil nutrient status directly affects plant 300 lM of N. Overall, Poa exerted a competitive responses to increases in temperature and Antarctic effect on Deschampsia but only at the higher temper- soils are highly variable in nutrient supply. Thus, in ature and higher N availability. At 5°/11 °C the this study we experimentally assessed the interaction competitive response of Deschampsia to Poa was of between the non-native Poa with the two native similar magnitude to the competitive effect of P. Antarctic vascular plant species at two different Deschampsia, and the competitive effect was greater temperatures and levels of nutrient availability. with at low N. The competitive effect of Poa was similar to the competitive response of Colobanthus to Poa at both temperatures and N levels. Thus, at low L. A. Cavieres (&) Á A. K. Sanhueza Á temperatures and N soil content the native Antarctic G. Torres-Mellado species might withstand Poa invasion, but this might Departamento de Botańica, Facultad de Ciencias Naturales y Oceanogra´ficas, Universidad de Concepcioń, change with climate warming. Concepcioń, Chile e-mail: [email protected] Keywords Antarctica Á Plant invasion Á Warming Á Competition Á Poa annua Á Deschampsia antarctica Á L. A. Cavieres Á A. K. Sanhueza Instituto de Ecologıá y Biodiversidad (IEB), Santiago, Colobanthus quitensis Chile A. Casanova-Katny Nućleo de Estudios Ambientales (NEA), Facultad de Recursos Naturales, Universidad Cato´lica de Temuco, Temuco, Chile 123 1598 L. A. Cavieres et al. Introduction and the relatively simple community structure of Antarctic ecosystems suggest that they might be Climate change and biological invasions are key particularly sensitive to the colonization and spread components of the global changes induced by human of non-native species (Frenot et al. 2005). These activities on the world biota (Sala et al. 2000). include some non-native vascular plants which have Although both processes negatively affect diversity colonized the Antarctic region (Chwedorzewska 2008; (Vila` et al. 2011; Bellard et al. 2012; Pysˇek et al. Olech and Chwedorzewska 2011; Pertierra et al. 2012), their effects were usually considered separately 2013). This has been attributed to increase in human (Dukes and Mooney 1999; Walther et al. 2002, 2009). activities and accelerated climate change (Hughes and However, it is now understood that climate change and Convey 2010). However, it is not clear if increases in biological invasions are linked, with climate change temperature in Antarctica can have synergistic effects influencing the rate and extent of biological invasions on the success of non-native invasive species already (e.g. Hellmann et al. 2008; Sorte et al. 2013; present in this continent. In addition, it has been Blumenthal et al. 2016). suggested that warmer conditions may favor the There are good reasons to expect that the rate and performance of the native species (e.g. Gerighausen extent of biological invasions can be influenced by et al. 2003; Cannone et al. 2016), challenging the climate change (Dukes and Mooney 1999; Walther potential advantage of non-native species over natives. et al. 2009; Ziska and Dukes 2014). For example, in Thus, the interaction between native and non-native warmer conditions, alien species originating from Antarctic vascular plants is a good model for evalu- warmer regions could spread to historically cold areas ating synergistic effects between climate change and (Walther et al. 2009) or increase their negative impacts invasion potential. if they are already there (Hellmann et al. 2008). Poa annua L. (Poaceae) has been reported in Verlinden and Nijs (2010) conducted a field study in several locations along the Antarctic Peninsula and Belgium where they exposed native and invasive adjacent islands, but the only large and permanent species to warmer conditions and found that while population has been observed in King George Island in invasive species showed no response, native species the vicinity of the Polish Antarctic Station Henry became less productive, suggesting that warmer Arctowsky (Chwedorzewska et al. 2015). The species conditions represent an indirect advantage for invasive was initially recorded in the austral summer of species through the negative effects of warming on 1985/86 in front of the entrance of the main building natives. Recently, Blumenthal et al. (2016) reported of the Arctowsky station (in metal grids used to clean that artificial warming increased the growth and shoes, Olech 1996). Since this first record, P. annua reproduction of the invasive grass Bromus tectorum has increased in density and abundance (Chwe- in semi-arid grasslands of North America, indepen- dorzewska 2008; Olech and Chwedorzewska 2011) dent of the presence of native competitors or the fact around the Arctowski station, where human activities that warming decreased soil moisture. Thus, syner- have damaged the natural substrate (Olech 1996; gistic interactions between invasion and climate Chwedorzewska et al. 2015). Eradication actions for change can increase the problems created by the this species have been initiated (Galera et al. 2016), presence of non-native organisms (Bradley et al. 2010; but they are not complete and removal is not a Compagnoni and Adler 2014; Ziska and Dukes 2014). guarantee of eradication as seeds may remain viable in However, synergistic effects between climate change the soil (Wo´dkiewicz et al. 2014). Poa annua is native and invasion are not the rule (see Sorte et al. 2013 for a to regions with cold-temperate climate (Pertierra et al. review), and a deeper understanding of where and how 2017); suggesting that its spread and impact may they might occur is important. increase as climate warms (Chown et al. 2012; Duffy Until recently the Antarctic continent was quite et al. 2017). The Antarctic Peninsula warmed rapidly pristine with regard to invasive organisms, but the (about 3.7 °C) in the last part of the past century increase in human activities in the last decades have (Turner 2013). However, Turner et al. (2016) reported increased the arrival of non-native organisms (Frenot that warming in the Antarctic Peninsula (AP) has et al. 2005; Hughes and Convey 2010; Chown et al. stopped in the last decade, but warned that warming 2012; Hughes et al. 2015). The low species richness episodes are likely to occur in the future. Ludescher 123 Invasive competition with native Antarctic plants 1599 et al. (2017) applying new analytical approaches to between warming and invasion success of P. annua long-term temperature records along the AP indicated under different soil nutrient conditions. while in some places there was no evidence of We experimentally assessed the intensity of com- significant warming (e.g. Rothera station petition and the competitive response of the interac- 1978–2013) there were others where warming has tion between the non-native invasive P. annua with been significant (e.g. Faraday–Verdnasky the two Antarctic native vascular plant species C. 1951–2013). Lee et al. (2017) pointed out that the quitensis and D. antarctica at two different tempera- recently paused warming observed in the AP is a tures and nutrient availabilities. As P. annua is a consequence of short-term natural climate variability highly competitive species of temperate origin (Holm and that new warming phase will be observed across 1997), we hypothesized that the competitive effect of the AP. P. annua on the Antarctic natives will be higher with There is concern that P. annua may transform into a the increase in temperature. Also, as this invasive much more aggressive invasive species in Antarctica. species prefers nutrient rich soils, this synergistic Studies with young and small individuals (0.6–2.0 mg effect between higher temperature and invasive neg- fresh weight) under controlled conditions have eval- ative effect on native is expected to be particularly uated the interaction among P. annua and the only two evident at high N. At lower nitrogen availabilities the Antarctic vascular plants (Deschampsia

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