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The Benefits of Breeding Crops that Produce Deep Roots
Kell, D.B. 2011. Breeding crop plants with deep roots: their role in sustainable carbon, nutrient and water sequestration. Annals of Botany 108: 407-418.

What was done
In a "Viewpoint" article published in the Annals of Botany, Douglas Kell -- who holds joint appointments at the University of Manchester's School of Chemistry and its Interdisciplinary Biocentre, as well as the UK's Biotechnology and Biological Sciences Research Council -- discusses the many benefits to be reaped from the breeding of crops that produce deeper and more "bushy" root systems than they do currently.

What was learned
Kell recounts how broader and deeper roots result in "much greater steady-state trapping of carbon, and also of nutrients and water, leading to improved drought and flooding tolerance, greater biomass yields, and better soil structure and steady-state carbon sequestration," noting that crops with such root systems "seem to mobilize and retain nutrients and water very effectively over extended periods, thus providing resistance to drought (e.g. Burch and Johns, 1978; Passioura, 1983, 2006; Ekanayake et al., 1985; Champoux et al., 1995; Price et al., 2002; Kato et al., 2006; Kirkegaard et al., 2007; Bernier et al., 2008; Kamoshita et al., 2008; Karcher et al., 2008; Cairns et al., 2009; Hund et al., 2009; McKenzie et al., 2009)." He also notes how the same phenomenon provides resistance to "flooding and other consequences of climate change, as well as to fertilizer runoff," while providing still further evidence in support of "the role of roots in improving soil structure (Gregory et al., 2010), on improving hydrology (MacLeod et al., 2007) and in showing that soil organic carbon improves agronomic productivity (Lal, 2010)." And in describing what could be called the super-payoff of a breeding program that he feels could essentially double the rooting volume of earth's crops, Kell calculates that "increasing soil carbon in the steady state by just 15% would lower atmospheric CO2 by 30%," which consequence would provide a powerful negative feedback to whatever global warming impetus earth's rising atmospheric CO2 concentration might possibly be producing.

What it means
Although Kell's analysis is significant in its own right, the ongoing rise in the air's CO2 content produces essentially the same results, as it typically stimulates plant root growth, as indicated by the many reviews of pertinent papers archived in our Subject Index under the general heading of Roots. Therefore, it can be appreciated that nature is already at work on the project Kell envisions. And if mankind was also to embark on the program he proposes, the two-pronged approach could ultimately lead to a new steady-state condition of the planet, whereby its atmospheric CO2 concentration stabilizes at an equilibrium value somewhat higher than that of the present, which consequence would result in greater plant water use efficiencies and crop yields than those of the present, but which would produce a climate that is not a whole lot different from that of today.

Bernier, J., Atlin, G.N., Serraj, R., Kumar, A. and Spaner, D. 2008. Breeding upland rice for drought resistance. Journal of the Science of Food and Agriculture 88: 927-939.

Burch, G.J. and Johns, G.G. 1978. Root absorption of water and physiological responses to water deficits by Festuca arundinacea Schreb. and Trifolium repens L. Australian Journal of Plant Physiology 5: 859-871.

Cairns, J.E., Audebert, A., Mullins, C.E. and Price, A.H. 2009. Mapping quantitative trait loci associated with root growth in upland rice (Oryza sativa L.) exposed to soil water-deficit in fields with contrasting soil properties. Field Crops Research 114: 108-118.

Champoux, M.C., Wang, G., Sarkarung, S., Mackill, D.J., O'Toole, J.C., Huang, N. and McCouch, S.R. 1995. Locating genes associated with root morphology and drought avoidance in rice via linkage to molecular markers. Theoretical and Applied Genetics 90: 969-981.

Ekanayake, I.J., O'Toole, J.C., Garrity, D.P. and Masajo, T.M. 1985. Inheritance of root characters and their relations to drought resistance in rice. Crop Science 25: 927-933.

Gregory, A.S., Webster, C.P., Watts, C.W., Whalley, W.R., MacLeod, C.J.A., Joynes, A., Papadopoulos, A., Haygarth, P.M., Binley, A., Humphreys, M.W., Turner, L.B., Skot, L. and Matthews, G.P. 2010. Soil management and grass species effects on the hydraulic properties of shrinking soils. Soil Science Society of America Journal 74: 753-761.

Hund, A., Ruta, N. and Liedgens, M. 2009. Rooting depth and water use efficiency of tropical maize inbred lines, differing in drought tolerance. Plant and Soil 318: 311-325.

Kamoshita, A., Babu, R.C., Boopathi, N.M. and Fukai, S. 2008. Phenotypic and genotypic analysis of drought-resistance traits for development of rice cultivars adapted to rainfed environments. Field Crops Research 109: 1-23.

Karcher, D.E., Richardson, M.D., Hignight, K. and Rush, D. 2008. Drought tolerance of tall fescue populations selected for high root/shoot ratios and summer survival. Crop Science 48: 771-777.

Kato, Y., Abe, J., Kamoshita, A. and Yamagishi, J. 2006. Genotypic variation in root growth angle in rice (Oryza sativa L.) and its association with deep root development in upland fields with different water regimes. Plant and Soil 287: 117-129.

Kirkegaard, J.A., Lilley, J.M., Howe, G.N. and Graham, J.M. 2007. Impact of subsoil water use on wheat yield. Australian Journal of Agricultural Research 58: 303-315.

Lal, R. 2010. Enhancing eco-efficiency in agro-ecosystems through soil carbon sequestration. Crop Science 50: S120-S131.

McLeod, M., Moran, D., Eory, V., Rees, R.M., Barnes, A., Topp, C.F.E., Ball, B., Hoad, S., Wall, E., McVittie, A., Pajot, G., Matthews, R., Smith, P. and Moxey, A. 2010. Developing greenhouse gas marginal abatement cost curves for agricultural emissions from crops and soils in the UK. Agricultural Systems 103: 198-209.

McKenzie, B.M., Bengough, A.G., Hallett, P.D., Thomas, W.T.B., Forster, B. and McNicol, J.W. 2009. Deep rooting and drought screening of cereal crops: a novel field-based method and its application. Field Crops Research 112: 165-171.

Passioura, J.B. 1983. Roots and drought resistance. Agricultural Water Management 7: 265-280.

Passioura, J.B. 2006. Increasing crop productivity when water is scarce -- from breeding to field management. Agricultural Water Management 80: 176-196.

Price, A.H., Steele, K.A., Gorham, J., Bridges, J.M., Moore, B.J., Evans, J.L., Richardson, P. and Jones, R.G.W. 2002. Upland rice grown in soil-filled chambers and exposed to contrasting water-deficit regimes. I. Root distribution, water use and plant water status. Field Crops Research 76: 11-24.

Reviewed 14 December 2011