Programmed cortical cell death as a driver of root exudation in barley and maize genotypes

Root-derived carbon (C) inputs via root exudates are a key pathway linking crops to soil C and nutrient cycling. Yet, it remains insufficiently understood how programmed cell death (PCD) processes such as root cortical senescence or aerenchyma formation control root exudation. In cereals, PCD processes can lower the metabolic costs of soil exploration and reshape radial transport and rhizosphere interactions. These anatomical strategies may therefore influence both the magnitude and composition of rhizodeposition. Here, we assessed whether genotypic contrasts in cortical cell death are reflected in root exudation patterns in two cereal species.

We compared five barley (Hordeum vulgare) and six maize (Zea mays) genotypes obtained from the IPK genebank in Gatersleben and from University of Bonn selected for contrasting root anatomical properties. Plants were grown in pots for one month in a common garden experiment. Root morphology was quantified via root scanning (e.g., total root length and root surface area), and root biomass was determined. Root exudates were collected using a semi-hydroponic hybrid system and analysed for dissolved organic carbon (DOC), soluble sugars, and phenolic compounds (CGA equivalents); amino acid analyses are ongoing. After root exudation sampling, two cm long root sections were sampled from each node. Samples were taken 5-8 cm behind the root tip. Root anatomy was imaged and root cortical senescence and aerenchyma formation were quantified and are currently analysed.

Across barley genotypes, exudate DOC, sugars and phenolics showed limited differentiation during. In contrast, maize exhibited pronounced genotypic variation in root system size (root surface area, total root length) and biomass, accompanied by genotype-specific exudation profiles. Total C exudation per root surface area were lowest in Zea141 and highest in Zea90 and Zea3426, while sugar exudation was reduced in Ky228, Zea141 and Zea294 relative to other genotypes.

Overall, our results reveal strong genotype dependence of rhizodeposition in maize but comparatively conservative early patterns in barley under the tested conditions. Ongoing analyses of root cortical senescence and aerenchyma will directly test whether genotypes exhibiting greater PCD show altered root exudation pattern providing a mechanistic basis for trait-based selection of cereal genotypes to enhance root-derived C inputs to soils.