Gwenzi, W, Veneklaas, EJ, Phillips, I, Bleby, TM & Hinz, C 2009, 'Spatial distribution of fine roots on a rehabilitated bauxite residue disposal area in Western Australia', in AB Fourie & M Tibbett (eds), Mine Closure 2009: Proceedings of the Fourth International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 317-327, https://doi.org/10.36487/ACG_repo/908_24
Root spatial distribution controls water and nutrient uptake, and is a key input in ecohydrological and
biogeochemical models. In particular, fine roots are responsible for resource acquisition and represent the
most dynamic component of root biomass. While root distribution on natural and agro-ecosystems is
relatively well documented, few studies have investigated root spatial distribution on rehabilitated mined
ecosystems, where adverse physical and chemical conditions may limit root growth. The authors investigated
the spatial distribution of fine roots (< 4.5 mm diameter) on a rehabilitated bauxite residue disposal area
under Mediterranean conditions. The objectives of this study were: to determine the vertical and horizontal
spatial variability of fine roots at plot scale; to develop a spatial model for root distribution for use in
ecohydrological modelling and other numerical applications; and to compare observed results to those
reported in literature for natural ecosystems under similar climatic conditions.
A 20 × 20 cm grid sampling scheme was used to collect 226 core samples (10 cm diameter and 10 cm
height) from a 700 cm long and 150 cm deep trench. Samples were analysed for root length (L), root
diameter (D), root length density (RLD) and root biomass density (RBD). Soil dry bulk density, pH and
electrical conductivity (EC) were used as indicators of soil physical and chemical constraints to root growth.
Root characteristics showed high spatial variability with coefficient of variation (CV) ranging from
51–200%. The top 20 cm had the highest mean RLD (8.4 cm cm-3) and root mass density (RMD) (1 g cm-3)
which decreased with depth according to a power function (RLD = 2474 × (SD)-1.8, r2 = 0.92). About 80% of
the total root length and biomass were in the top 40 cm, while the remainder was in the deeper layers (40–
140 cm). At all depths, very fine roots (≤ 1.5 mm in diameter) constituted about 95% of the total root length,
suggesting a root system adapted for water uptake in the dry season when soil moisture is limited. Soil EC
values were generally low (mean 1.1 dS m-1), but showed high spatial variability (CV = 91%) probably due
to non-uniform incorporation of chemical amendments. For 19 out of the 24 samples, EC values were below
2.5 dS m-1, considered the upper limit for normal plant growth. Soil pH was slightly alkaline (mean of 8.2),
and showed low spatial variability (CV = 4%). In all cases, bulk densities (mean = 1.3 g cm-3) were below
the critical value for restricted root growth (1.6 g cm-3). Correlation analysis suggested that root distribution
was not limited by soil dry bulk density, pH and EC. Accordingly, the depth distribution of cumulative RLD
and RMD closely agreed (r2 = 0.93) with the general root depth distribution models for natural vegetation
ecosystems in Mediterranean climates. The results are discussed in the context of vegetation water uptake on
rehabilitated mined ecosystems.
Arunachalam, S.K., Hinz, C. and Aylmore, G. (2004) Soil physical properties affecting root growth in rehabilitated gold
mine tailings, SuperSoil 2004, 3rd Australian New Zealand Soils Conference, 5–9 December 2004, University of
Sydney, Australia, pp. 1–7.
Blake, G.R. and Hartge, K.H. (1986) Bulk density, In Methods of Soil Analysis Part 1, A. Klute (ed), ASA Monograph,
No. 9, 2nd edition, Madison, Wisconsin, USA, pp. 363–376.
Bouillet, J.P., Laclau, J.P., Arnaud, M., M’Bou, A.T., Saint-André, L. and Jourdan, C. (2002) Changes with age in the
spatial distribution of roots of Eucalyptus clone in Congo, impact on water and nutrient uptake, for Ecol Manage,
Vol. 171, pp. 43–57.
Courtney, R.G. and Timpson, J.P. (2005) Reclamation of fine fraction bauxite processing residue (red mud) amended
with coarse fraction residue and gypsum, Water, Air, and Soil Pollution, Vol. 164, pp. 91–102.
Gale, M.R. and Grigal, D.K. (1987) Vertical root distributions of northern tree species in relation to successional status,
Canadian Journal of Forest Research, Vol. 17, pp. 829–834.
Hendrick, R.L. and Pregitzer, K.S. (1996) Temporal and depth related patterns of the fine root dynamics in northern
hardwood forests, Journal of Ecology, Vol. 84, pp. 167–176.
Jackson, R.B., Canadell, J., Ehleringer, J.R., Mooney, H.A., Sala, O.E. and Schulze, E.D. (1996) A global analysis of
root distributions for terrestrial biomes, Oecologia, Vol. 108, pp. 389–411.
Jacobs, D.F. and Timmer, V.R. (2005) Fertilizer-induced changes in rhizosphere electrical conductivity: relation to
forest tree seedling root system growth and function, New Forests, Vol. 30, pp. 147–166.
Kage, H. (1997) Is low rooting density of faba beans a cause of high residual nitrate content of soil at harvest? Plant and
Soil, Vol. 190, pp. 47–60.
Laclau, J.P., Arnaud, M., Bouillet, J.P. and Ranger, J. (2001) Spatial distribution of Eucalyptus roots in a deep sandy
soil in the Congo: relationships with the ability of the stand to take up water and nutrients, Tree Physiology,
Vol. 21, pp. 129–136.
Liedgens, M. and Richner, W. (2001) Minirhizotron observations of the spatial distribution of the maize root system,
Agronomy Journal, Vol. 93, pp. 1097–1104.
Mengler, F.C., Kew, G.A., Gilkes, R.J. and Koch, J.M. (2006) Using instrumented bulldozers to map spatial variation in
the strength of regolith for bauxite mine floor rehabilitation, Soil and Tillage Research, Vol. 90, pp. 126–144.
Millikin, C.S. and Bledsoe, C.S. (1999) Biomass and distribution of fine and coarse roots from blue oak (Quercus-
douglasii) trees in the northern Sierra Nevada foothills of California, Plant and Soil, Vol. 214, pp. 27–38.
Rayment, G.E. and Higginson, F.R. (1992) Australian laboratory handbook of soil and water chemical methods, Inkata
Press, Melbourne, 330 pp.
Ecosystem reconstruction and pedogenesis
Mine Closure 2009, Perth, Australia 327
Rokich, D.P., Meney, K.A., Dixon, K.W. and Sivasithamparam, K. (2001) The impact of soil disturbance on root
development in woodland communities in Western Australia, Australian Journal of Botany, Vol. 49,
Scanlon, B.R., Levitt, D.G., Keese, K.E., Reedy, R.C. and Sully, M.J. (2005) Ecological controls on water-cycle
response to climate variability in deserts, In Proceedings of the National Academy of Science, Vol. 102(17),
Schenk, H.J. (2008) The shallowest possible water extraction profile: A null model for global root distribution, Vadose
Zone Journal, Vol. 7, pp. 1119–1124.
Szota, C., Veneklaas, E.J., Koch, J.M. and Lambers, H. (2007) Root Architecture of Jarrah (Eucalyptus marginata)
Trees in Relation to Post-Mining Deep Ripping in Western Australia, Restoration Ecology, Vol. 15(14)
(Supplement), pp. S65–S73.
Thompson, P.J., Jansen, I.J. and Hooks, C.L. (1987) Density as parameters for predicting root system performance in
mine soils, Soil Science Society of America Journal, Vol. 51, pp. 1288–1293.
Wilcox, C.S., Ferguson, J.W., Fernandez, G.C.J. and Nowak, R.S. (2004) Fine root growth dynamics of four Mojave
Desert shrubs as related to soil moisture and microsite, Journal of Arid Environments, Vol. 56, pp. 129–148.