Reduced Lateral Root Branching Density Improves Drought Tolerance in Maize

Abstract

An emerging paradigm is that root traits that reduce the metabolic costs of soil exploration improve the acquisition of limiting soil resources. Here, we test the hypothesis that reduced lateral root branching density will improve drought tolerance in maize (Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length (few but long [FL] and many but short [MS]) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit of axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water isotopic signature, signifying deeper water capture, 51% to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves drought tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the drought tolerance of maize and possibly other cereal crops.

Drought stress and carbon assimilation in a warming climate: Reversible and irreversible impacts

“…However, these processes may be highly relevant in plants subjected to abiotic stresses. The paradigm that deep rooting is important for drought tolerance of plants was recently questioned (Grieder et al, 2014;Nippert and Holdo, 2015), but large cortical cells in maize roots (Chimungu et al, 2014) and lateral root development (smaller number and increased length) were found to be well correlated with drought tolerance (Zhan et al, 2015). Leaf CO2 assimilation and stomatal conductance were considerably increased in maize lines with large root cortical cells compared to lines with smaller ones (Chimungu et al, 2014).…”

Corn root morphoanatomy at different development stages and yield under water stress

“…In corn, it has been shown that greater root length (Ali et al, 2016) and fewer lateral roots (Zhan et al, 2015) lead to an increase in drought tolerance. The size of the root cortex and the amount of aerenchyma are characteristics that are heritable and desirable in corn breeding for drought tolerance (Burton et al, 2015).…”

The race to create super-crops

“…Tests in US fields starved of nitrogen showed 3 that maize with few long lateral roots produced yields more than 30% higher than maize with many short lateral roots. The longlateral-root variety performed even better in a test of drought-like conditions, where it showed a 144% increase in yield 4 . Other research teams are taking different approaches to breeding fertilizer-frugal crops.…”

“…The ability to grow deep roots is influenced by several factors, including the characteristics of a plant's lateral roots -those that grow out of the main framework of roots. Working in maize, or corn (Zea mays), Lynch found that plants perform better under low-nitrogen conditions 3 and water stress 4 when they have just a few long lateral roots rather than many short ones. This arrangement requires less energy to grow, so plants can invest more resources in aboveground vegetation and developing deep roots that can suck up water and nitrogen.…”