Root morphological and structural comparisons of introduced and native aquatic plant species in multiple substrates

Invasions of introduced plants are considered among the greatest threats to biodiversity worldwide. Aquatic habitats suffer invasion more frequently and extensively than do terrestrial habitats. Although the role of roots in plant anchoring and support is important, previous studies have focused much attention on the morphological traits of above-ground parts, with relatively less attention given to the root structures of aquatic plants. In this study, we aimed to compare differences in root morphological and structural traits between introduced and native plants in response to different substrates. We hypothesized that introduced aquatic plants have an advantage over native plants with regard to root trait values and plasticity. A total of six aquatic plants were used: Two invasive and one exotic noninvasive species were paired with their native counterparts according to life form (amphibious emergent, submerged and floating-leaved) and cultivated in substrates of clay, a clay/sand mixture (v:v = 1:1) or sand. Root morphological traits, topological indices and root relative distance plasticity indices were quantified. The results indicated that different substrates have various effects on the root traits of these six aquatic plants; the introduced plants generally exhibited higher plasticity than did their native counterparts of the same life form.