Genetic Variation in Root Architectural Traits in Lactuca and Their Roles in Increasing Phosphorus-Use-Efficiency in Response to Low Phosphorus Availability

Abstract

Low phosphorus (P) bioavailability in the soil and concerns over global P reserves have emphasized the need to cultivate plants that acquire and use P efficiently. Root architecture adaptation to low P can be variable depending on species or even genotypes. To assess the genetic variability of root architectural traits and their responses to low P in the Lactuca genus, we examined fourteen genotypes including wild species, ancient and commercial lettuce cultivars at low (LP, 0.1 mmol. L–1) and high P (HP, 1 mmol. L–1). Plants were grown in cylindrical pots adapted for the excavation and observation of root systems, with an inert substrate. We identified substantial genetic variation in all the investigated root traits, as well as an effect of P availability on these traits, except on the diameter of thinner roots. At low P, the main responses were a decrease in taproot diameter, an increase in taproot dominance over its laterals and an increase in the inter-branch distance. Although the genotype x P treatment effect was limited to root depth, we identified a tradeoff between the capacity to maintain a thick taproot at low P and the dominance of the taproot over its laterals. Regardless of the P level, the phosphorus-use-efficiency (PUE) varied among lettuce genotypes and was significantly correlated with total root biomass regardless of the P level. As taproot depth and maximum apical diameter were the principal determinants of total root biomass, the relative increase in PUE at low P was observed in genotypes that showed the thickest apical diameters and/or those whose maximal apical diameter was not severely decreased at low P availability. This pre-eminence of the taproot in the adaptation of Lactuca genotypes to low P contrasts with other species which rely more on lateral roots to adapt to P stress.

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“…A higher root length and finer root systems in plants are often interpreted in terms of response to a high level of N [ 22 , 36 ]; in lettuce enhanced root length, density at high N is reported [ 34 , 37 ]. Controversial behaviour is recorded for phosphorus: P deficiency is found to promote [ 38 , 39 ] or reduce [ 40 ] root proliferation, depending on species, but often results in finer root systems (e.g., [ 41 , 42 ]). In lettuce under low P, Beroueg et al [ 40 ] reported a higher taproot growth with lower branching, although branch diameters were finer.…”

“…Controversial behaviour is recorded for phosphorus: P deficiency is found to promote [ 38 , 39 ] or reduce [ 40 ] root proliferation, depending on species, but often results in finer root systems (e.g., [ 41 , 42 ]). In lettuce under low P, Beroueg et al [ 40 ] reported a higher taproot growth with lower branching, although branch diameters were finer.…”

Assessing phosphorus efficiency and tolerance in maize genotypes with contrasting root systems at the early growth stage using the semi‐hydroponic phenotyping system

“…The results of Beroueg et al. (2021) showed that low P stress inhibited primary root length and reduced lateral root number in 14 Lactua genotypes, while the degree of reduction varied among genotypes. P stress resulting from low P supply in soil reduced lateral root density in rice (Vejchasarn et al., 2016) and common bean (Borch et al., 1999).…”

Sustainable Cannabis Nutrition: Elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality

“…There are also differences in PUE among cultivars of crop plants in the field ( Horst et al., 1993 ; Ciarelli et al., 1998 ; Rose et al., 2007 ; Powers et al., 2020 ; Beroueg et al., 2021 ). Differences in root architecture is a major contributor to this variability, with some cultivars more capable of increasing absorptive surface area under low P conditions.…”

“…Differences in root architecture is a major contributor to this variability, with some cultivars more capable of increasing absorptive surface area under low P conditions. ( Shenoy and Kalagudi, 2005 ; Beroueg et al., 2021 ). Cultivars can also vary in their ability to modify the rhizosphere by releasing organic acids and increasing the solubility of P in calcareous soils ( Shenoy and Kalagudi, 2005 ), but this is not typically beneficial in controlled environment agriculture where adequate fertilizer is continuously supplied and substrate pH is tightly controlled.…”