Future roots for future soils.

Jonathan P Lynch,Christopher F Strock,Sacha J Mooney,Hannah M Schneider

doi:10.1111/pce.14213

Abstract

Mechanical impedance constrains root growth in most soils. Crop cultivation changed the impedance characteristics of native soils, through topsoil erosion, loss of organic matter, disruption of soil structure and loss of biopores. Increasing adoption of Conservation Agriculture in high‐input agroecosystems is returning cultivated soils to the soil impedance characteristics of native soils, but in the low‐input agroecosystems characteristic of developing nations, ongoing soil degradation is generating more challenging environments for root growth. We propose that root phenotypes have evolved to adapt to the altered impedance characteristics of cultivated soil during crop domestication. The diverging trajectories of soils under Conservation Agriculture and low‐input agroecosystems have implications for strategies to develop crops to meet global needs under climate change. We present several root ideotypes as breeding targets under the impedance regimes of both high‐input and low‐input agroecosystems, as well as a set of root phenotypes that should be useful in both scenarios. We argue that a ‘whole plant in whole soil’ perspective will be useful in guiding the development of future crops for future soils.

Highlights

We focus on how root adaptations to mechanical impedance may have evolved over time, and are continuing to evolve, in response to changing soil environments
We propose that ongoing changes in the soil environments of both high‐input and low‐input agroecosystems may present divergent physical constraints for soil exploration by roots
We propose that Multiseriate cortical sclerenchyma (MCS) is an adaptive trait for soil resource acquisition in modern agroecosystems

Summary

| INTRODUCTION

In high‐input agroecosystems, intensive use of fertilizers, pesticides and irrigation causes large‐scale environmental pollution and unsustainable resource depletion (Foley et al, 2011; Woods et al, 2010). Conservation Agriculture: In high‐input agroecosystems, traditional tillage in mechanized agriculture is evolving towards reduced tillage, which will return to some of the features of native soil, including greater topsoil organic matter, greater frequency of biopores, greater aggregate development and improved soil structure, but harder bulk soil, and greater N availability in deep strata because of nitrate leaching from fertilizer (Figure 6c). Climate change is forecast to intensify water deficit stress in many high‐input agroecosystems, and so drought‐induced soil hardening, especially in the topsoil, will be an important constraint to root growth This will create a scenario in which a soil environment more like that of native soils will confer fitness benefits to plants with more ancestral root phenotypes in terms of mechanical impedance (Figure 6c). Dense root hairs will be increasingly useful in future soils as we work to make high‐input systems less demanding and more resilient, and low‐input systems more productive (Lynch, 2019)

Cheap roots

Developmental regulation of root plasticity in cereal crops

Findings

Developmental regulation of root plasticity in dicot crops