The four species studied differed significantly in terms of survival, total biomass, root/shoot ratio and stem height (Table ).
Table 2. Effects of species, locality and treatment (simulated shading, and nutrient and moisture levels) on survival (number of seedlings alive) of the four Impatiens species recorded at the end of the experiment and tested using generalized linear models, and (more ...)
Under control conditions (50 % Knopp solution, optimal moisture, full light), I. parviflora survived best (97·5 % of the plants were alive at the end of the experiment), followed by I. glandulifera, I. noli-tangere and I. capensis. Shading and low nutrients resulted in increased survival in all the species, reaching 100 % in I. glandulifera and I. parviflora. High nutrient levels decreased survival in two of the invasive species, I. capensis and I. glandulifera. Drought and flooding reduced the survival of I. glandulifera and I. noli-tangere, but not that of I. parviflora and I. capensis (Table ).
Biomass produced by I. glandulifera greatly exceeded that of other species. The only exception to this trend was that I. glandulifera plants grown in shade had biomass comparable with that of I. parviflora, the second most productive species regardless of the environment (Fig. ). Although seedlings of I. glandulifera produced most biomass, their stems were tallest only when grown in shade (Fig. ). The native I. noli-tangere produced less biomass and was usually shorter than the two invasive species (Fig. ). The potentially invasive I. capensis performed similarly to I. noli-tangere in terms of total biomass but only under high nutrient concentration where its biomass was considerably lower (Fig. ). Its stems were among the tallest in most of the environments (Fig. ). Impatiens parviflora allocated more biomass to roots than the other species in all treatments except simulated shading (Fig. ).
Fig. 1 Total biomass, stem height and root/shoot ratio of native and invasive Impatiens species recorded in the different treatments; species are indicated in the key. The points denote averages for plants from three localities for I. noli-tangere and I. capensis (more ...)
The response in terms of total biomass, root/shoot ratio and stem height of individual species to shading, and nutrient and moisture levels (species × treatment interactions, Table ) differed. Variation in shading and nutrient levels accounted for substantially more of the variability in these traits than did moisture (Tables and ). Low levels of nutrients resulted in decreased total biomass and stem height and an increased root/shoot ratio, with plasticity being the highest in all three traits in I. glandulifera (Fig. ). Simulated shading triggered intensive stem elongation, with the highest plasticity recorded in I. glandulifera (Fig. ). The other environments did not result in the same response in species' traits. The total biomass of invasive species was lower in all the treatments, but that of I. parviflora and I. capensis was greater in the flooding and simulated shading treatments. On the other hand, the biomass of native I. noli-tangere markedly increased when provided with high levels of nutrients and simulated shading, and its plasticity was greater than that of the invasive species (Fig. ).
Effects of locality and treatment (simulated shading, and nutrient and moisture levels) on stem height, total biomass and root/shoot ratio tested using ANOVA
Fig. 2 Plasticity in total biomass, stem height and root/shoot ratio of native and invasive Impatiens species in response to individual treatments; species are indicated in the key. The plasticity of individual species was calculated as the average value recorded (more ...)
The highest average plasticity (0·67 averaged across all traits and environments in which plants survived to the end of the experiment) was recorded for I. glandulifera, followed by I. noli-tangere (0·50), I. capensis (0·47) and I. parviflora (0·45). The highest proportion of variability explained by the treatments, expressed as R2 averaged across traits and treatments, was recorded for I. glandulifera (0·47), followed by I. parviflora (0·37), I. noli-tangere (0·25) and I. capensis (0·23). However, the patterns were highly specific (Table ); high levels of plasticity, i.e. ≥ |0·4|, were recorded for all species, environments and traits (Fig. ) and R2 over 0·3 for all species, traits and treatments, except moisture levels (Table ).
Table 4. The results of an ANOVA of the phenotypic plasticity exhibited by the four species of Impatiens tested in terms of response of stem height, total biomass and root/shoot ratio of different populations to simulated shading, and different levels of nutrients (more ...)
Local differentiation within species
A significant effect of the locality from which the seeds were collected was found in control plants of all species and for all traits except the root/shoot ratio in I. noli-tangere (Table ). Under the control conditions, the highest variability explained by locality was recorded for I. capensis (0·396), followed by I. parviflora (0·392), I. glandulifera (0·254) and I. noli-tangere (0·212). For plants under the treatments, I. capensis exhibited the highest variability (0·199), followed by I. parviflora (0·130), I. noli-tangere (0·116) and I. glandulifera (0·067) when averaging across all traits and treatments. In I. parviflora and I. capensis the locality significantly affected all the traits in all the treatments. In I. glandulifera there were significant or close to significant differences among localities, except for biomass in response to simulated shading. Impatiens noli-tangere exhibited significant differences only in four out of nine cases. However, the variability explained by locality was in general lower than that explained by the treatments. Locality explained more variability than treatment only in those treatments that had little effect (Tables and ). This was most frequently recorded in I. capensis and less frequently in I. glandulifera (Table ).