RUSSELL REVIEW Are plant roots only “in” soil or are they “of” it? Roots, soil formation and function

Abstract

Roots are near-ubiquitous components of soils globally but have often been regarded as separate from the soil rather than a substantial factor in determining what soil is and how it functions. The start of rapid soil formation commenced about 400 million years ago with the emergence of vascular plants and the evolution of roots and associated microbes. Roots and associated microorganisms contribute significantly to soil formation by altering rocks and soil minerals through a variety of biogeochemical processes and supply carbon to a depth that can have long residence times. Living root inputs of carbon via rhizodeposits are more efficient than shoot and root litter inputs in forming slow-cycling, mineral-associated soil organic carbon pools. The current functionality of soils in providing food and fuel and fibres, supplying plant nutrients, filtering water and flood regulation, and disease suppression are all dependent on the activities of plant roots. Roots are actively communicating and collaborating with other organisms for mutual benefit, and the signals underlying this modulation of the rhizosphere microbiome are being identified. In this review I examine how plant roots (an organ not an organism) affect soil formation and function and conclude that, from several perspectives, roots are not just "in" soil but "of" it and that definitions of soil should recognise this. A possible definition is: "Soils are altered surficial rock or sediment, composed of organic matter, minerals, fluids, and organisms whose formation and functionality are influenced by biogeochemical weathering and interactions of these components with plant roots." Highlights • Paleoclimatic and paleosoil research shows the key role of roots and mycorrhiza in soil formation.• Deep roots and living root inputs are substantial contributors to long-term C storage.• Root/microbe signalling facilitates mutualistic symbioses, nutrient uptake and disease suppression.

Fertilizers and Fertilization Strategies Mitigating Soil Factors Constraining Efficiency of Nitrogen in Plant Production

“…Here, we discuss the key processes related to root system growth during the growing season. The functions of the root system of crop plants can be considered from several points of view [ 48 , 49 , 50 ]: Anchorage of the plant in the soil; Water extraction from the soil to: stabilize the shoot temperature transport nutrients to the shoot; Nutrient uptake from the soil solution; Impact on rhizosphere processes through: release of organic compounds → a source of energy for microorganisms present in the rhizosphere release of protons or chelating agents → increase in nutrient availability deposition of carbon by dead roots → humus build-up; Symbiotic associations with bacteria or fungi; Storage organs, treated as main yield (sugar beets, cassava, sweet potato). …”

“…Here, we discuss the key processes related to root system growth during the growing season. The functions of the root system of crop plants can be considered from several points of view [48][49][50]:…”

New insights into high soil strength and crop plants; implications for grain crop production in the Australian environment

“…The soil matrix is a complex environment with many physical, chemical and biological interactions (Gregory 2022). In terms of soil strength, the primary determinant is soil pore structure, a consequence of relationships between the soil particle sizes and their packing arrangement.…”

Cover crop influence on pore size distribution and biopore dynamics: Enumerating root and soil faunal effects

“…Soil structure, i.e., the arrangement of solids and pores, defines most soil functions and processes ( Rabot et al, 2018 ). Plant roots are the main modifiers of the pore structure, affecting it through a variety of mechanisms, including direct creation/modification of soil pores, increases in soil organic matter (SOM), exudation of mucilage, and water uptake ( Gregory, 2022 ). A growing root interacts with pore structure in several ways: (1) roots can elongate into the soil matrix containing only the pores smaller than the root diameter (2) they can grow along an existing pores including biopores and (3) they can negotiate an existing pore at some angle before penetrating the soil ( Jin et al, 2017 ; Lucas, 2022 ).…”