The growth and phosphorus acquisition of invasive plants Rudbeckia laciniata and Solidago gigantea are enhanced by arbuscular mycorrhizal fungi

Abstract

While a number of recent studies have revealed that arbuscular mycorrhizal fungi (AMF) can mediate invasive plant success, the influence of these symbionts on the most successful and high-impact invaders is largely unexplored. Two perennial herbs of this category of invasive plants, Rudbeckia laciniata and Solidago gigantea (Asteraceae), were thus tested in a pot experiment to determine whether AMF influence their growth, the concentration of phosphorus in biomass, and photosynthesis. The following treatments, including three common AMF species, were prepared on soils representative of two habitats that are frequently invaded by both plants, namely fallow and river valley: (1) control-soil without AMF, (2) Rhizophagus irregularis, (3) Funneliformis mosseae, and (4) Claroideoglomus claroideum. The invaders were strongly dependent on AMF for their growth. The mycorrhizal dependency of R. laciniata was 88 and 63 % and of S. gigantea 90 and 82 % for valley and fallow soils, respectively. The fungi also increased P concentration in their biomass. However, we found different effects of the fungal species in the stimulation of plant growth and P acquisition, with R. irregularis and C. claroideum being the most and least effective symbionts, respectively. None of AMF species had an impact on the photosynthetic performance indexes of both plants. Our findings indicate that AMF have a direct effect on the early stages of R. laciniata and S. gigantea growth. The magnitude of the response of both plant species to AMF was dependent on the fungal and soil identities. Therefore, the presence of particular AMF species in a site may determine the success of their invasion.

Keywords: Arbuscular mycorrhiza (AM); Arbuscular mycorrhizal fungi (AMF); Asteraceae; Giant goldenrod; Golden glow; Plant invasions.

Fig. 1

Mycorrhizal colonization (percentages; mean ± SD) of Rudbeckia laciniata and Solidago gigantea grown in the fallow and river valley soils. Mycorrhizal parameters: mycorrhizal frequency (F), relative mycorrhizal root length (M), and relative arbuscular richness (A) (see the “Materials and methods” section for a description of these parameters). Within each plant species, the lowercase letters above the bars indicate the statistically significant interaction between the fungus and soil effects; the capital letters show the significant main effect of the fungus; the different letters above the bars indicate statistically significant differences; the asterisks (*) indicate the significant main effect of the soil; for each P < 0.05 (see Table 2 for details on the main effects and interactions)

Fig. 2

Shoot and root mass (g; mean ± SD) of Rudbeckia laciniata and Solidago gigantea grown in the fallow and river valley soils. Within each plant species, the lowercase letters above the bars indicate the statistically significant interaction between the fungus and soil effects; the different letters above the bars indicate statistically significant differences; for each P < 0.05 (see Table 2 for details)

Fig. 3

Photosynthetic performance index (PI_ABS; mean ± SD) of Rudbeckia laciniata and Solidago gigantea grown in the fallow and river valley soils. Within each plant species, the asterisks (*) indicates the significant main effect of the soil (P < 0.05) (see Table 2 for details)

Fig. 4

Concentrations of phosphorus (mg per kg dry weight; mean ± SD) in the shoots and roots of Rudbeckia laciniata and Solidago gigantea grown in the fallow and river valley soils. Within each plant species, the lowercase letters above the bars indicate the statistically significant interaction between the fungus and soil effects; the different letters above the bars indicate statistically significant differences; for each P < 0.05 (see Table 2 for details)

Fig. 5

Principal component analysis ordination diagram (PC 1 vs. PC 2) of Rudbeckia laciniata and Solidago gigantea parameters (M—relative mycorrhizal root length, shoot and root mass, P concentration in the shoots and roots, PI_ABS - photosynthetic performance index) for samples of the two soil types and four fungal treatments. The percentage of total variance as explained by each axis is shown