Toward an Integrated Root Ideotype for Irrigated Systems

Abstract

Breeding towards root-centric ideotypes can be a relatively quick trait-based strategy to improve crop resource use efficiency. Irrigated agriculture represents a crucial and expanding sector, but its unique parameters require traits distinct from previously proposed rainfed ideotypes. We propose a novel irrigated ideotype that integrates traits across multiple scales to enhance resource use efficiency in irrigated agroecosystems, where resources are concentrated in a relatively shallow 'critical zone'. Unique components of this ideotype include rapid transplant recovery and establishment, enhanced exploitation of localized resource hotspots, adaptive physiological regulation, maintenance of hydraulic conductivity, beneficial rhizosphere interactions, and salinity/waterlogging avoidance. If augmented by future research, this target could help to enhance agricultural sustainability in irrigated agroecosystems by guiding the creation of resource-efficient cultivars.

Impact of Irrigation Strategies on Tomato Root Distribution and Rhizosphere Processes in an Organic System

“…In our organic SDI system, the localized placement of organic fertilizer overlaps with constant soil moisture likely creating a resource-rich hotspot around the drip line (Figure 1 and Supplementary Figure S2). This resource pattern requires a root ideotype with prolific fine lateral roots and high uptake rate to efficiently utilize soil available nutrients in the hotspot (Schmidt and Gaudin, 2017). The low root-zone nitrate-N and high plant N concentrations observed in SDI plants, despite their relatively small root system, provide evidence for efficient exploitation of the resource-rich hotspot via localized root proliferation.…”

“…In contrast, under FI, the organic N source was mixed throughout the upper 20 cm of soil and was subjected to more intensive wet-dry cycles (Figure 1). This resource pattern requires roots to explore and forage in a larger soil area and remain relatively unresponsive to water fluctuations (Hodge, 2009;Schmidt and Gaudin, 2017). The development of a thicker and diffuse root system in the FI system enables plants to explore larger soil area and adapt to intensive dry-wet cycles (Jackson and Bloom, 1990;Zotarelli et al, 2009a).…”

“…Plants can regulate root system development to maximize acquisition of soil moisture and nutrient resources whose distribution is affected by irrigation (Jin et al, 2017;Schmidt and Gaudin, 2017). This plasticity can be achieved through different strategies including spatially targeted root proliferation to mine nutrient-and moisture-rich patches while avoiding resourcepoor areas (Hodge, 2009).…”

“…Plasticity occurs over time as well: plants can develop rapid root regrowth along with increased root physiological activity, such as N uptake and hydraulic conductivity, following the soil rewetting caused by rainfall or irrigation events (BassiriRad and Caldwell, 1992;Huang and Eissenstat, 2000). A better understanding of root responses to wetting patterns caused by different irrigation strategies will contribute to the design of new resource-saving irrigation technologies and the development of effective root ideotypes for irrigated landscapes (Schmidt and Gaudin, 2017).…”

“…Integrating rhizosphere processes mediated by root-associated microbes with root developmental patterns is also necessary to enhance our mechanistic understanding of plant adaptation to resource availability under different irrigation strategies (Schmidt and Gaudin, 2017). Soil microorganisms participate in vital biogeochemical processes that influence plant nutrient uptake and nutrient retention (Bardgett et al, 2014).…”