Reversible and irreversible root phenotypic plasticity under fluctuating soil physical conditions

Hanna Sjulgård,Daniel Iseskog,Norbert Kirchgessner,A Glyn Bengough,Thomas Keller,Tino Colombi

doi:10.1016/j.envexpbot.2021.104494

Hanna Sjulgård, Daniel Iseskog + Show 4 more

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https://doi.org/10.1016/j.envexpbot.2021.104494

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Abstract

Roots grow in a highly heterogeneous physical environment due to the spatial complexity of soil structure. Thereby, the root growth zone repeatedly experiences soil physical stress such as hypoxia or increased penetration resistance. To mimic the highly variable physical environment surrounding the root growth zone, we subjected pea and wheat seedlings to periodic soil physical stress. One day of soil hypoxia or increased penetration resistance reduced root elongation rate of both species by at least 20 %. Upon stress release, root elongation rate of pea could recover within one day, while no such recovery occurred in wheat. Similarly, the diameter of the root elongation zone in pea increased by 15 % and 20 % due to hypoxia and increased penetration resistance, respectively, but decreased again once the stresses were released. In contrast, the diameter of the elongation zone of wheat roots started to decrease with the onset of soil physical stress and this trend continued upon stress release. Hence, root responses to short-term soil physical stress were reversible in pea and irreversible in wheat, indicating reversible and irreversible root phenotypic plasticity, respectively. This suggests that strategies to cope with periodic soil physical stress may vary among species. The differentiation between reversible and irreversible phenotypic plasticity is crucial to advance our understanding on soil exploration, resource acquisition, whole plant growth, and ultimately crop yield formation on structured soil.

Highlights

The spatial complexity of soil structure causes large heterogeneity in soil physical properties and conditions at the sub-millimetre scale (Dexter, 1988; Jin et al, 2013; Schlüter et al, 2019; Walter et al, 2009; Wang et al, 2020)
Soil structure refers to the arrangement of solids and pores (Angers and Caron, 1998) and strongly influences soil physical properties that are key to root growth such as penetration resistance and soil oxygen concentration (Bengough et al, 2011; Jin et al, 2013)
Root elongation rate of pea and wheat grown under optimal soil physical conditions during the entire experiment did not change significantly over time (Supplemental Fig. S3)

Summary

Introduction

The spatial complexity of soil structure causes large heterogeneity in soil physical properties and conditions at the sub-millimetre scale (Dexter, 1988; Jin et al, 2013; Schlüter et al, 2019; Walter et al, 2009; Wang et al, 2020). Soil structure refers to the arrangement of solids and pores (Angers and Caron, 1998) and strongly influences soil physical properties that are key to root growth such as penetration resistance and soil oxygen concentration (Bengough et al, 2011; Jin et al, 2013). Soil gas transport rates decrease with increasing soil moisture, while soil penetration resistance increases when soil dries (Bailey-Serres et al, 2012; Bengough et al, 2011; Whitmore and Whalley, 2009). Understanding how plants respond to these heterogeneities and how this affects soil exploration and resource acquisition is crucial to improve the sustainability of crop production (Wang et al, 2020)

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