Root phenotypes for improved nutrient capture: an underexploited opportunity for global agriculture

Abstract

Summary Nutrient‐efficient crops are a solution to the two grand challenges of modern agriculture: improving food security while reducing environmental impacts. The primary challenges are (1) nitrogen (N) and phosphorus (P) efficiency; (2) potassium (K), calcium (Ca), and magnesium (Mg) efficiency for acid soils; and (3) iron (Fe) and zinc (Zn) efficiency for alkaline soils. Root phenotypes are promising breeding targets for each of these. The Topsoil Foraging ideotype is beneficial for P capture and should also be useful for capture of K, Ca, and Mg in acid soils. The Steep, Cheap, and Deep ideotype for subsoil foraging is beneficial for N and water capture. Fe and Zn capture can be improved by targeting mechanisms of metal mobilization in the rhizosphere. Root hairs and phenes that reduce the metabolic cost of soil exploration should be prioritized in breeding programs. Nutrient‐efficient crops should provide benefits at all input levels. Although our current understanding is sufficient to deploy root phenotypes for improved nutrient capture in crop breeding, this complex topic does not receive the resources it merits in either applied or basic plant biology. Renewed emphasis on these topics is needed in order to develop the nutrient‐efficient crops urgently needed in global agriculture.

Inoculation with the mycorrhizal fungus Rhizophagus irregularis modulates the relationship between root growth and nutrient content in maize (Zea mays ssp. mays L.)

“…With regard to Mg, transcripts encoding Mg transporters are known to accumulate to higher levels in wheat following mycorrhizal inoculation (Li et al, 2018). In common with P, the elements S, Ca and Mg are often poorly available due to low-mobility and formation of conjugates with other soil compounds (Kelly and Barber, 1991; Scherer, 2001; Lynch, 2019). As such, hyphal foraging and delivery of these nutrients by mycorrhizal fungi would be predicted to be of potential benefit to plants under field conditions.…”

“…In addition, nutrient distribution varies across soil horizons: poorly-mobile nutrients such as phosphorus (P), potassium (K), magnesium (Mg) or calcium (Ca) are typically enriched in topsoil, while more mobile nutrients, such as nitrogen (N), are typically more abundant deeper in the soil (Rubio et al, 2003; Ho et al, 2004; Lynch and Brown, 2008; Postma et al, 2014; Rangarajan et al, 2018). As a consequence, researchers have distinguished RSAs optimized for topsoil versus deeper foraging (Lynch, 2019).…”

Metabolic alterations provide insights into Stylosanthes roots responding to phosphorus deficiency

“…Cumulative studies show that the adaptive strategies of plant to P deficiency include changes in root architecture and morphology, such as promotion of lateral root growth, enhancement of root hair development and formation of cluster roots in Proteaceae plants [4]. Such developmental strategies increase the root-soil contact surface, and thus facilitating exploitation of Pi reserves from soils [9]. In this study, root dry weight, root length, root surface area and root volume were significantly increased in stylo under low P treatment for 10 and 15 d, suggesting that stylo adapts to P deficiency through modification of root growth (Fig.…”

“…Plants have evolved a series of adaptive mechanisms to enhance P acquisition efficiency (PAE) and P utilization efficiency (PUE) in Pi-limited soils [8]. The major adaptive strategies of plant increasing PAE include modification of root architecture and morphology [9], exudation of organic acids from root to rhizosphere [10], secretion of phosphatases and ribonucleases [11], enhancing the expression of Pi transporter [12] and symbiosis with arbuscular mycorrhiza (AM) or other plant growthpromoting rhizobacteria (PGPR) [13]. The dominant PUE-related strategies include replacement of membrane phospholipids by galactolipids and sulfolipids [14], remobilization Pi from the vacuolar P storage [15], and alternative metabolic bypass reactions, for example inorganic pyrophosphate (PPi) instead of Pi [16].…”

Predicting metabolism during growth by osmotic cell expansion

“…Because of the energy cost of synthesising cellular macromolecules such as protein, lipid and carbohydrates (Schwender and Hay, 2012), it is generally assumed that synthesis of new cells is more expensive than expanding existing cells (Lynch, 2019;Taiz, 1992). However, even during cell expansion, new macromolecules need to be produced and the synthesis and accumulation of osmolytes to drive cell expansion also represents a significant cost.…”