Microplastic additions modulate intraspecific variability in root traits and mycorrhizal responses across root-life history strategies

Microplastics (MP) are recognized as a major pollutant in terrestrial
environments, prompting concerns regarding their effects on plant-soil
dynamics. Despite evidence of MP altering soil physicochemical properties,
impacts on belowground root traits and arbuscular mycorrhizal (AM) fungi
remains poorly explored. Existing research has mainly centered on a few
model plant species, emphasizing root biomass, and often employs single
polymer types and addition rates that surpass realistic
scenarios.  To investigate how environmentally relevant mixtures
and concentrations of MPs impact plant growth, root trait expression and
AM fungal colonization, we conducted a greenhouse experiment using six
plant species chosen for their contrasting root life strategies; three
species in the Amaryllidaceae family represented resource conservation
root traits (Allium fistulosum (Onion), Allium tuberosum (Chive), Allium
porrum (Leek)), and three from the Solanaceae family, represented plants
with resource acquisitive root traits (Solanum lycopersicum (Tomato),
Solanum melongena (Eggplant), Capsicum annuum (Pepper). MP treatments
consisted of control (0% MP), low (0.1% w/w) and high (1% w/w) MP
additions, using an environmentally relevant MP mixture of weathered
polymer types and shapes. Above and belowground biomass, average root
trait expression (specific root length (SRL), average root diameter (D)
and root tissue density (RTD), AM fungal colonization, as well as
intraspecific variability across MP addition treatments.  We
found that the addition of environmentally relevant additions of MPs was
species specific and not determined by root life-strategy. MPs increased
biomass in Leek, Eggplant and Tomato, while decreasing AM fungal
colonization in Tomato. MP additions had no discernible impact on average
root functional trait expression across species. However, the addition of
MPs resulted in altered intraspecific variability in root traits and AM
fungal colonization, indicating a mechanism for plant tolerance to
MPs.  To address the impacts of MP on plant functioning, our
study highlights the need for future research to focus on environmentally
relevant mixtures of MPs, considering various plant species’ capacities to
tolerate soil contamination and the potential for tipping points under
real-world conditions.