The role of fine root morphology in nitrogen uptake by riparian plants.

Aim: In agricultural basins, riparian buffers maintained along stream channels reduce nitrogen (N) concentrations in agricultural runoff, thereby improving water quality. Investigating the role of riparian vegetation in the related processes will provide insights into the mechanisms by which riparian zones retain soil N. Methods: In our study, the proportion of plant N uptake, fine root (diameter < 1mm) biomass and fine root morphology at five soil depths (0-15, 15-30, 30-45, 45-60, and 60-75 cm) for Acorus calamus, Canna indica and Phragmites communis were measured in Taihu Lake Basin. Results: The soil layer from which the majority of N was absorbed was 0-15 cm (50.8±1.0, 56.0±1.4 and 37.5±3.2% for A. calamus, C. indica, and P. communis, respectively). The N uptake from 45 to 75 cm for P. communis (21.2±2.2%) was significantly higher than A. calamus (14.9±0.7%) and C. indica (9.2±1.5%) (P < 0.05). Our results showed that N uptake was directly proportional to root morphological characteristics such as specific root surface area (SRA, P < 0.05) and specific root length (SRL, P < 0.01), but the relationships varied among species. Changes in environmental factors caused by soil depth strongly influenced some of the root morphological indicators (e.g., fine root biomass, mean diameter (D)). Conclusions: Soil environmental factors and plant root morphology jointly influenced plant N uptake. During vegetation selections of the riparian restoration projects, plants with high SRL or SRA should be given priority due to their expected high capacity in N uptake. But cautions need to be taken as the positive relationships between SRL and SRA and plant N uptake may vary between plant species. Optimal selection of diverse species with complementary nutrient uptake strategies could maximize N uptake at various soil depths and overall N removal from agricultural runoff. [ABSTRACT FROM AUTHOR]