Abstract
The ability of plants to take up water from the soil depends on both the root architecture and the distribution and evolution of the hydraulic conductivities among root types and along the root length. The mature maize (Zea mays L.) root system is composed of primary, seminal, and crown roots together with their respective laterals. Our understanding of root water uptake of maize is largely based on measurements of primary and seminal roots. Crown roots might have a different ability to extract water from the soil, but their hydraulic function remains unknown. The aim of this study was to measure the location of water uptake in mature maize and investigate differences between seminal, crown, and lateral roots. Neutron radiography and injections of deuterated water were used to visualize the root architecture and water transport in 5-week-old maize root systems. Water was mainly taken up by crown roots. Seminal roots and their laterals, which were the main location of water uptake in younger plants, made a minor contribution to water uptake. In contrast to younger seminal roots, crown roots were also able to take up water from their most distal segments. The greater uptake of crown roots compared with seminal roots is explained by their higher axial conductivity in the proximal parts and by the fact that they are connected to the shoot above the seminal roots, which favors the propagation of xylem tension along the crown roots. The deeper water uptake of crown roots is explained by their shorter and fewer laterals, which decreases the dissipation of water potential along the roots.
Highlights
In view of the increasing demand for food by the growing population and of the limiting water availability in many countries, there is an urgent need to understand what root properties facilitate the extraction of water from drying soils (Bishopp and Lynch, 2015)
Water was mainly taken up by crown roots. Seminal roots and their laterals, which were the main location of water uptake in younger plants, made a minor contribution to water uptake
The root architecture of a 5-week-old maize plant consisted of a primary root and seminal roots with long laterals and crown roots that emerged from the above-ground part of the plant 2 weeks after planting
Summary
In view of the increasing demand for food by the growing population and of the limiting water availability in many countries, there is an urgent need to understand what root properties facilitate the extraction of water from drying soils (Bishopp and Lynch, 2015). There is limited information on the function of the different root types in extracting water from the soil. The maize root stock has a unique architecture that comprises several root types forming at different developmental stages (Hochholdinger et al, 2004). The embryonic primary and seminal roots together with their laterals constitute the major. The post-embryonic shoot-borne roots (i.e. crown roots) become the major backbone of the maize root system (Hochholdinger, 2009)
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