There is much interest in the concept of sustainable intensification of agriculture as one of the actions that can contribute to a reduction in food insecurity for the future. Environmental stress can significantly limit plant productivity through an impact on a variety of processes which contribute to carbon gain and to the development of the canopy and reproductive structures. If we are to minimise these restrictions of growth and yielding, it is important to understand the mechanistic basis of these responses. For more sustainable use of water and nutrients in crop production, it is also important to understand the biology behind resource use efficiency by crops

We highlight here the importance of the influence of both hydraulic and chemical signaling on the regulation of functioning, growth and development of plants under stress and suggest that by processing and responding to these signals, plants are able to regulate growth and development relative to the availability of  resources required for growth and development. We propose that via enhancement or suppression of different ‘root signal’ cascades we can intervene to sustain plant yielding under different environmental stresses (Morison et al. 2007). We review the identity of signals limiting leaf conductance, leaf growth and harvest index (e.g Foulkes et al. 2010) and consider prospects for manipulation of signaling, with special reference to the impact of changes in sap pH, modified fluxes of abscisic acid (ABA) and of the ethylene precursor ACC  (e.g. Jia and Davies, 2007; Wilkinson and Davies, 2010).

While there are many genetic opportunities to modify stress signaling cascades to increase crop yield, crop improvement cannot immediately combat changes in the climate and increases in food demand that are happening now. It is therefore important that we use novel crop management techniques to impact some of the same biology. For example, techniques such as deficit irrigation, fertilizer  placement and buffer treatments can all impact long distance ABA/ACC/CK signaling. Manipulation of  rhizosphere organisms can also change the plant’s signaling capacity (e.g. Belimov et al. 2009) and the plant’s sensitivity to abiotic stresses such as soil drying. Such manipulations may be a cost-effective way to sustain yielding and increase water use efficiency in dryland agriculture.

Belimov, A.A., Dodd, I.C., Hontzeas, N., Theobald, J.C., Safronova, V.I., and Davies, W.J. (2009) Rhizosphere bacteria containing ACC deaminase increase yield of plants grown in drying soil via both local and systemic hormone signalling. New Phytologist 181, 413-423.

Foulkes, M.J., Slafer, G.A., Davies, W.J., Berry, P.M., Sylvester-Bradley, R., Martre, P., Calderini, D.F. Griffiths, S.  and  Reynolds, M.P. (2010) Raising yield potential in wheat. III. Optimizing partitioning to grain while maintaining lodging resistance. Journal of Experimental Botany 62, 469-486

Jia,. W. and Davies, W.J. (2007) Modification of leaf apoplastic pH in relation to stomatal sensitivity to root sourced ABA signals. Plant Physiology 143, 68-77.

Morison, J.I.L., Baker, N.R., Mullineaux, P.M. and Davies, W.J. (2007) Improving water use in crop production. Phil. Trans. Royal Soc. Special Issue on Sustainable Agriculture 363, 639-658.

Wilkinson, S. and Davies, W.J. (2010) Drought, ozone, ABA and ethylene: new insights from cell to plant to community. Plant Cell and Environment 33, 510-525.