Author for correspondence: zarah.pattison@stir.ac.uk Running title: Impatiens plant-soil feedbacks Word count: 6225 Summary Impatiens glandulifera is one of the most widespread invasive plant species in the UK. Although aspects of its biology are known, there is little information about its association with microbial communities both above- and below-ground. Furthermore, it is unknown whether this species exhibits any form of plant-soil feedback (PSF), commonly seen in other invasive weeds. We conducted a PSF experiment, in which plants of I glandulifera were grown in soil that supported the species, and compared with those in a control soil from the same locality. Soil nutrients were measured and the soil and foliar microbial communities were assessed. I. glandulifera grew larger and faster in conditioned soil compared to the control. Higher levels of phosphate were also found in conditioned soils. Arbuscular mycorrhizal fungal (AMF) colonisation was lower in conditioned soils, suggesting that I. glandulifera may rapidly alter AMF communities in invaded areas. PSFs had a significant effect on the foliar endophyte community, with clear separation of species between conditioned and control soils. These results show that I. glandulifera displays a positive PSF and the PSF mechanism extends beyond the soil microbial community to affect foliar endophytes. The observed increase in endophytes in plants grown in conditioned soil could enhance resistance to herbivory, thus further accentuating the invasive properties of this species.
Plants from Phase 2 were evaluated for AMF colonisation using the acidified ink staining method of Vierheilig et al. (1998). Plants were removed from their pot and roots washed free of soil. A 2-5 g sub-sample from each root system was immersed in a 10% potassium hydroxide solution (10% w/v: 10g KOH in 100ml aqueous solution) and placed in a water bath at 80°C for 25 minutes. Thereafter roots were rinsed with water and blotted dry. Roots were placed in clean vials and covered with staining solution (84.4: 15: 0.6, dH2O: 1% HCI: Quink blue pen ink) in the water bath for a further 15 minutes. Colonisation was measured using the cross hair eye piece method of McGonigle et al. (1990). Statistical analysis All analyses were conducted using plants from Phase 2 as replicates. All data sets were checked for normality and homogeneity of variances prior to analyses and all percentage data were arc sine transformed. All data violating assumptions of homogeneity were transformed with logarithmic or reciprocal transformations. Linear mixed effect models (LMM) using the nlme package in R (Pinheiro et al., 2012) was used to assess plant height and total leaf number, as a response to the interaction between treatment and time. Plant replicate was assigned as a random effect. Exploratory analyses of the data revealed that the explanatory variable ’time’ was quadratic. The quadratic term was only retained within the model alongside the associated main effect when significant. A one-way ANOVA was used to examine soil treatment effects on fresh and dry biomass, as well as soil NO3, PO4 and K content and percentage root length colonized (% RLC) by AMF. One-way ANOVA’s were used to compare total mass of PLFAs, mass of bacteria attributed PLFAs alone and mass of fungal attributed PLFAs alone between invaded and native (control) soil. PLFA community analysis (Principal Component Analysis; PCA) was performed in R (R Core Team, 2014) by
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