Large root systems: are they useful in adapting wheat to dry environments?

Abstract

Abstract. There is little consensus on whether having a large root system is the best strategy in adapting wheat (Triticum aestivum L.) to water-limited environments. We explore the reasons for the lack of consensus and aim to answer the question of whether a large root system is useful in adapting wheat to dry environments. We used unpublished data from glasshouse and field experiments examining the relationship between root system size and their functional implication for water capture. Individual root traits for water uptake do not describe a root system as being large or small. However, the recent invigoration of the root system in wheat by indirect selection for increased leaf vigour has enlarged the root system through increases in root biomass and length and root length density. This large root system contributes to increasing the capture of water and nitrogen early in the season, and facilitates the capture of additional water for grain filling. The usefulness of a vigorous root system in increasing wheat yields under water-limited conditions maybe greater in environments where crops rely largely on seasonal rainfall, such as the Mediterranean-type environments. In environments where crops are reliant on stored soil water, a vigorous root system increases the risk of depleting soil water before completion of grain filling.Additional keywords: root biomass, root length, root length density, root system size, water capture.

Water: the most important ‘molecular’ component of water stress tolerance research

“…Recent work examining Arabidopsis thaliana showed that shoot and root growth are indeed under the same genetic control (Bouteillé et al 2012; and references therein). These results suggest that any advantages conferred by bigger root systems in terms of additional water extraction might be offset by the presence of a larger shoot consuming the extra water (Palta et al 2011). Two recent modelling studies showed exactly that: faster root growth generally led to faster soil water depletion, which subsequently led to yield penalties in soybean ) and chickpea .…”

“…This raises the question as to whether root and shoot growth are under independent or coordinated genetic controls. Root and shoot growth is indeed closely coordinated (Jackson 1993;Palta et al 2011), and abscisic acid (ABA) likely plays a major role in that regulation (Munns and Cramer 1996). It is, in fact, critical for plants to maintain a hydraulic integrity in the soil-root-xylem-leaf-atmosphere continuum to maintain water fluxes (Kudoyarova et al 2013).…”

“…For example, a simulation study indicated that maize yields would increase if the root depth increased (Sinclair and Muchow 2001). Hammer et al (2009) postulated that changes in root architecture contributed to maize yield increases in the USA These examples illustrate that roots may not be the answer to all water stress scenarios and that their contribution to yield increases in water-limited environments depends on the crop and the stress conditions (Palta et al 2011). In summary, although there is no doubt that roots are important, their role in adapting to water stress might have been overstated.…”

Management of crop water under drought: a review

“…Increasing importance of subsoil moisture for crop performance implies an advantage of strongly explorative root systems (Kirkegaard et al 2007;Wasson et al 2012). Particularly spring sown cereals may profit from quick root depth penetration to avoid early drought, making better use of post-winter water resources in deeper soil layers (Palta et al 2011). Sustained growth during periods of early season water deficit furthermore enhances quick canopy coverage, thereby reducing soil evaporation and saving stored soil water for crop transpiration.…”

“…For wheat, physiological and root research studies evidence the significant contribution of roots to higher drought resistance (e.g. Sanguineti et al 2007;Manschadi et al 2008;Palta et al 2011). Wasson et al (2012) give an overview of selection strategies for root improvement of wheat in Australia.…”