Root nutrient concentration and biomass allocation are more plastic than morphological traits in response to nutrient limitation

Understanding the magnitude of phenotypic plasticity within a species is important, particularly when comparing species from diverse habitats or when using traits from global databases. Our objective was to quantify the magnitude of intraspecific variability of fine root, stem, and leaf traits in response to nutrient availability. We measured growth rates and traits from fine roots, stems, and leaves on replicate seedlings of four species grown in two treatments: low and high soil nutrient availability. We used ANOVA to test for effects of fertilizer, species, and their interaction on trait expression, and ranked intraspecific trait variation using the coefficient of variation. Root nutrient concentration, relative growth rate, and biomass allocation exhibited the most plastic responses to nutrient availability. Specific root length, specific leaf area, root diameter, and wood density were the least variable traits within species. Nutrient limitation only induced greater root branching in the non-mycorrhizal Proteaceae species that produced more cluster roots. Woody plants respond to nutrient limitation by increasing root mass fraction, rather than by adjusting root morphology or structure. We urge caution when using root tissue chemistry traits obtained from global databases in local studies, as this is one of the most plastic traits in response to nutrient availability.