Root responses of native and invasive forbs to resource heterogeneity

Soil nutrient heterogeneity is ubiquitous in natural systems, and a plant’s ability to exploit nutrients depends, in part, on root morphological plasticity.  Currently, rangelands of the arid West are being invaded by non-native species, which often out-compete their native counterparts.  We propose this greater competitive ability is linked to the greater morphological plasticity of invasive species in response to resource heterogeneity.  Our objective was to determine whether native and invasive plants differed in root foraging traits in response to heterogeneous nutrient distribution. We compared a suite of root-related traits among four native and four invasive species exposed to heterogeneous (patch) or homogeneous (control) nutrient distribution. In general, invasive species allocated more biomass belowground, regardless of treatment, having a greater root weight ratio than native species. Overall, invasive species had greater total root length, specific root length, and root length density in patch, compared to control, treatments.  However, there was great variability among native species’ root responses to nutrient heterogeneity, with some native species allocating more and some allocating less root biomass in patch relative to control treatments.  Creating many, thin roots in nutrient patches may increase invasive species’ ability to exploit soil nutrients, augmenting their competitive ability.  Given native species variable responses to nutrient heterogeneity, restoration efforts should focus on selecting those species with morphologically plastic root systems and potentially greater competitive ability.