Reduction in Root Secondary Growth as a Strategy for Phosphorus Acquisition

Abstract

We tested the hypothesis that reduced root secondary growth of dicotyledonous species improves phosphorus acquisition. Functional-structural modeling in SimRoot indicates that, in common bean (Phaseolus vulgaris), reduced root secondary growth reduces root metabolic costs, increases root length, improves phosphorus capture, and increases shoot biomass in lowphosphorus soil. Observations from the field and greenhouse confirm that, under phosphorus stress, resource allocation is shifted from secondary to primary root growth, genetic variation exists for this response, and reduced secondary growth improves phosphorus capture from low-phosphorus soil. Under low phosphorus in greenhouse mesocosms, genotypes with reduced secondary growth had 39% smaller root cross-sectional area, 60% less root respiration, 27% greater root length, 78% greater shoot phosphorus content, and 68% greater shoot mass than genotypes with advanced secondary growth. In the field under low phosphorus, these genotypes had 43% smaller root cross-sectional area, 32% greater root length, 58% greater shoot phosphorus content, and 80% greater shoot mass than genotypes with advanced secondary growth. Secondary growth eliminated arbuscular mycorrhizal associations as cortical tissue was destroyed. These results support the hypothesis that reduced root secondary growth is an adaptive response to low phosphorus availability and merits investigation as a potential breeding target.

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

“…These results have recently been supported by empirical results with maize, which show that genotypes with greater RCA formation have greater topsoil foraging, P capture, growth, and yield in low‐P soil than genotypes with less RCA, notwithstanding the reduction in mycorrhizal habitat by RCA formation (Galindo‐Castañeda et al ., ). In dicots, P stress inhibits the secondary growth of roots, and common bean genotypes with greater inhibition of secondary growth under P stress have reduced root costs, greater P capture, and greater growth in low‐P soil (Strock et al ., ; Fig. ).…”

“…Crop breeding for root architectural and anatomical phenotypes with better P capture could have important indirect consequences for AMS, however. For example, RCA formation, root cortical senescence, and reduced secondary growth all improve P capture, and all have important consequences for AMS by regulating the volume of AMS habitat in the root cortex (Galindo‐Castañeda et al ., ; Schneider & Lynch, ; Strock et al ., ). Architectural phenes that localize root foraging in shallow or deep soil domains may also affect AMS, since the propagules of fungal symbionts, as well as the foraging environments of extraradical hyphae, are more favorable in the topsoil (Lynch & Wojciechowski, ).…”

“…As already noted, anatomical phenotypes that reduce the metabolic cost of soil exploration improve the capture of P and N. They also improve the capture of water: increased RCA (Zhu et al ., ; Chimungu et al ., ), reduced cortical cell file number (Chimungu et al ., ), increased cortical cell size (Chimungu et al ., ), and possibly cortical senescence (Schneider & Lynch, ) improve water capture under drought. The reduction of mycorrhizal habitat in anatomical phenotypes that reduce cortical volume does not appear to counteract the major benefit that these phenotypes confer for soil exploration and P capture (Galindo‐Castañeda et al ., ; Strock et al ., ). RCA has the added benefit of improving root function under hypoxia, which is important for subsoil foraging (Lynch & Wojciechowski, ).…”

Sugars en route to the roots. Transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere

“…Currently, enhanced carbohydrate transport to the root has been demonstrated for nitrogen (N) and phosphorus (P) limitation (Hermans et al ). In the case of P limitation in common bean ( Phaseolus vulgaris ), it has been recently confirmed that secondary root growth is impaired in favor of root elongation, thus optimizing P acquisition under low P conditions (Strock et al ). This preferential C investment in primary root growth was also reported for Arabidopsis submitted to low Pi (Hanlon et al ).…”

Genetic components of root architecture and anatomy adjustments to water‐deficit stress in spring barley

“…Lynch () and Strock et al . () have reported that smaller root cross‐sectional area induced by plants adaptive response of decreased root secondary growth increases root length (for greater soil exploration) and improves the consumption of growth‐limiting resources. Growth allometry is induced by multiple cryptic genetic factors associated with local climate and abiotic stress response (Vasseur et al ., ), suggesting that the contrasting response of tiller and main‐shoot nodal roots may be an adaptive response to water deficit.…”