Root Hairs Matter at Field Scale for Maize Shoot Growth and Nutrient Uptake, But Root Trait Plasticity is Primarily Triggered by Texture and Drought

Abstract

Aims: Root hairs are important for uptake, especially for nutrients with low mobility in soils with high sorption capacity. Yet, this has rarely been demonstrated in the field during a whole growing season. Mutants with defective root hairs are expected to have lower nutrient uptake, unless they compensate with more root growth. Since root hairs can also contribute to the plant's water uptake their importance could change over the course of a growing season. Methods: The root hair mutant rth3 of Zea mays and the corresponding wild-type were grown for two years under field conditions on sand and loam.Results: Shoot growth and P and K uptake of the plants were promoted by the presence of hairs at all growth stages. Differences between genotypes were greater on loam than on sand until tassel emergence, because additional exploitation by hairs is more relevant in loam. Compensation for the absence of root hairs by increased root growth was not observed in absolute terms. The root to shoot ratio was higher for rth3 than for wild-type. Root traits showed high plasticity in response to texture, the most salient being a greater mean root diameter in sand, irrespective of genotype. The mechanism causing the increase in mean root diameter is still unknown. Root length density was higher in sand, which can be explained by a greater need for exploration than exploitation in this substrate. Conclusion: The greater investment in root growth on sand compared to loam is expected to alter the long-term carbon balance.

Development of mechanical soil stability in an initial homogeneous loam and sand planted with two maize (Zea mays L.) genotypes with contrasting root hair attributes under in-situ field conditions

“…The potential for further compaction, i.e., reduction of the pore space, had already been greatly reduced in sand in 2020, which becomes evident when looking at the extremely narrow ranges of C c . Together with declining C s in both substrates, this coincides with higher root length densities in all treatments in 2020 compared to 2019 (Vetterlein et al 2022). Increased root length densities bring about a stabilization of structure, hence higher σ pc and lower C c and C s .…”

“…The sample location was between rows of maize with a distance of 22 cm to the next plant. The position was in close proximity to the location used for root sampling in Vetterlein et al (2022) who took soil cores 10 cm from the foot of the maize plant. In preparation for the measurements, samples were saturated with tap water and subsequently put on ceramic suction plates until weight consistency was reached to obtain the desired matric potentials (Ψ m ) at the start of the measurements.…”

“…A tendency to higher energy values could be observed in WT, which was also the genotype with higher root length densities at all depths at BBCH83 (fig. 5 in Vetterlein et al 2022). Our undisturbed samples were taken within the depth intervals of this project partner, which did not show a pronounced depth gradient, thus enabling us to refer to them directly.…”

“…In particular, the combination of loam and WT resulted in higher forces compared to the other treatments at more negative Ψ m. WT had significantly higher shoot dry weight compared to rth3 (fig. 3 in Vetterlein et al 2022) in both years, resulting in higher water demand for WT and subsequently an earlier onset and a more severe drought stress. This process is reflected in the Ψ m measurements in sand made by Jorda et al (submitted).…”

“…We assume the higher soil moisture variability and therefore more frequent drying out processes up to the permanent wilting point (Jorda et al submitted) to be of major importance in this context. A further aspect might have been higher root length densities at BBCH83 at 14 cm depth in sand in both years and in loam in 2020 (Vetterlein et al 2022).…”