Root strategies - where trace elements occur heterogeneously in soil

Trace Elements (TE)s occur heterogeneously in soil. Depending on the soil’s origin, TE concentrations may change by an order of magnitude or more over just a few centimetres. The total concentration and distribution is a function of the parent material plus subsequent atmospheric or water-borne deposition.

The heterogeneous distribution of TEs in soil affects plant root growth. In some tree species, the roots avoid hotspots contaminated with TEs. Conversely, roots of the hyperaccumulator plant Thlaspi caerulescens actively forage zinc-rich hotspots in soils. The response of roots to heterogeneously distributed TEs may profoundly affect uptake as well as leaching of the trace element through the soil profile. The principles of how heterogeneously distributed TE affects root development is poorly understood.

Until recently, a lacuna of non-destructive measurement technologies has hampered the visualisation of the growth and activity of living roots. The Paul Scherrer Institut, Villigen, Switzerland has developed a facility to visualise roots in soil using neutron radiography and tomography. This technique enables the investigation of the response of roots to heterogeneously distributed TEs in soil. Neutron radiography can also reveal the water flux in the root zone.

Our current research at Lincoln University is using rhizoboxes to determine the response of roots of New Zealand native plants to patches of biosolids (sewage sludge) in soil.

Root strategy or root inhibition? A neutron radiograph of a lupine growing in a 150 x 150 x 10 mm aluminium slab containing soil partitioned with 20 mg/kg added B in a 50 mm vertical strip on the right hand side of the image. The left hand 100 mm contained no added B.
Root distribution and water flux The change in water content of the plant shown in above after the infiltration of 10 ml of water (A 1-2 min, B 2-5 min, C 28-40 min). The wet-front shows up as a dark band, while root water uptake is visible in B and C as a discontinuous grey area.

Related publications

Robinson BH, Bañuelos GS, Conesa HM, Evangelou MWH, Schulin R (2009). The phytomanagement of trace elements in soil. Critical Reviews in Plant Sciences 28(4), 240-266.

Moradi AB, Conesa HM, Robinson B, Lehmann E, Kuehne G, Kaestner A, Oswald S, Schulin R (2009). Neutron radiography as a tool for revealing root development in soil: capabilities and limitations. Plant and Soil 318 243–255.

Robinson BH, Moradi A, Schulin R, Lehmann E, Kaestner A (2008). Neutron radiography for the analysis of plant-soil interactions. In: Envyclopedia of Analytical Chemistry. Wiley InterScience. DOI 10.1002/9780470027318.a9023.

Menon M, Robinson B, Oswald S, Kaestner A, Abbaspour K, Lehmann E, Schulin R (2007). Visualization of root growth in heterogeneously contaminated soil using neutron radiography. European Journal of Soil Science 58, 802-810.

Robinson BH, Schulin R, Nowack B, Roulier S, Menon M, Clothier BE, Green SR, Mills TM (2006). Phytoremediation for the management of metal flux in contaminated sites. Forest, Snow and Landscape Research 80(2), 221-234.