Abstract
The strategy of producing rapid initial growth and establishing early in the growing season is important, and it is employed by invasive macrophytes. Elodea nuttallii and Egeria densa, two Hydrocharitaceae species, became weeds after invading many countries in recent years. Comparative studies on their invasive traits in relation to native species during winter and spring are limited. In the present study, we compared the growth performance of these two exotic species with a perennial native species, Potamogeton maackianus, in different water depths (1, 2, and 3 m) during winter (January and February) and spring (March and April). Three morphological traits (shoot number, root number and shoot length), total biomass, relative growth rate (RGR) and two physiological photosynthetic traits (total chlorophyll content and the maximum quantum yield of PSII [Fv/Fm]) were measured for each macrophyte. All three species could overwinter as entirely leafy plants. Biomass, RGR, morphological traits and physiological traits were all different among species. However, water depths had a significant effect only on morphological traits. At all water depths, E. nuttallii had significantly higher values for morphological traits, total biomass and RGR than P. maackianus, while E. densa had significantly fewer roots and a lower total chlorophyll content than P. maackianus. Except for Fv/Fm at a 3 m water depth, morphological and physiological photosynthetic traits, biomass and RGR of E. nuttallii were significantly higher than those of E. densa. In addition, a large number of adventitious roots developed from E. nuttallii but not from the other two species. These results indicate that the advantages of E. nuttallii to grow in winter and spring may make it more prone to expansion than E. densa in China.
Highlights
With the process of economic globalization and trade liberalization, many species are imported in places that are out of their indigenous geographical ranges, and some of them develop into invasive species (Richardson et al, 2000)
The shoot number and shoot length of E. nuttallii decreased and increased, respectively, while depth had no significant effect on the shoot traits of E. densa and P. maackianus (Figures 2A,B)
Water depth had no significant effect on the root number of E. nuttallii and E. densa, while the root number of P. maackianus at the 3 m depth was significantly lower than that of plants at the 1 and 2 m depths (Figure 2C)
Summary
With the process of economic globalization and trade liberalization, many species are imported in places that are out of their indigenous geographical ranges, and some of them develop into invasive species (Richardson et al, 2000). Numerous studies have considered invasive aquatic plants with regards to their growth, regeneration capacity, photosynthesis traits, genetic, reproductive, overwintering strategies and management (Lui et al, 2005; Hussner, 2009; Zhang et al, 2010; Wersal and Madsen, 2011; You et al, 2014; Liu et al, 2016; Hussner et al, 2017). The strategy of invasive macrophytes to produce rapid initial growth and establish early in the growing season may increase their competitive ability and allow them to successfully replace native species (Nichols and Shaw, 1986). The influence of water depth on the growth of invasive submerged species during the early growth season has not been well elucidated
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