Root morphological traits that determine phosphorus-acquisition efficiency and critical external phosphorus requirement in pasture species

Abstract

Annual pasture legume species can vary more than 3-fold in their critical external phosphorus (P) requirement (i.e. P required for 90% of maximum yield). In this work we investigated the link between root morphology, P acquisition and critical external P requirement among pasture species. The root morphology acclimation of five annual pasture legumes and one grass species to low soil P availability was assessed in a controlled-environment study. The critical external P requirement of the species was low (Dactylis glomerata L., Ornithopus compressus L., Ornithopus sativus Brot.), intermediate (Biserrula pelecinus L., Trifolium hirtum All.) or high (Trifolium subterraneum L.). Root hair cylinder volumes (a function of root length, root hair length and average root diameter) were estimated in order to assess soil exploration and its impact on P uptake. Most species increased soil exploration in response to rates of P supply near or below their critical external P requirement. The legumes differed in how they achieved their maximum root hair cylinder volume. The main variables were high root length density, long root hairs and/or high specific root length. However, total P uptake per unit surface area of the root hair cylinder was similar for all species at rates of P supply below critical P. Species that maximised soil exploration by root morphology acclimation were able to prolong access to P in moderately P-deficient soil. However, among the species studied, it was those with an intrinsic capacity for a high root-hair-cylinder surface area (i.e. long roots and long root hairs) that achieved the lowest critical P requirement.

The carboxylate‐releasing phosphorus‐mobilizing strategy can be proxied by foliar manganese concentration in a large set of chickpea germplasm under low phosphorus supply

“…The lack of the correlation between shoot P content and root hair length in the present study might be due to the relatively short root hair lengths of all chickpea genotypes (only 0.30–0.46 mm) compared with other plant species; for example, root hair lengths were 0.35–1.19 mm for five perennial pasture grass species grown in three low‐P acid soils (Haling et al ., ) and 0.50–0.75 mm for Dactylis glomerata , Ornithopus spp. and Biserrula pelecinus (Haling et al ., ). The findings of Haling et al .…”

“…Root hair length was analysed using the ImageJ program (US National Institute of Health, Bethesda, MA, USA) as described by Haling et al . (), with three randomly selected and homogenously distributed root hairs in each graph measured, giving a total of 15 (3 × 5 photos) root hair lengths per replicate. Specific root length was calculated as root length per unit root DW (Pang et al ., ).…”

“…Root hair cylinder volume was calculated as the volume of the cylinder enclosing the root and root hair zone, as done by Haling et al . (), using the following formula:…”

Belowground solutions to global challenges: special issue from the 9th symposium of the International Society of Root Research

“…Average root hair length was a key component of the Broot hair cylinder volume^which was strongly correlated with plant P uptake in the reports by Waddell et al (2016) and Haling et al (2016). The paper by Vincent et al (2016) reports work to substantially reduce the effort required to quantify root hair development in situ.…”

“…Similar to Waddell et al (2016), cultivars with greater soil exploration were also found to generally have superior growth and nutrient uptake by Haling et al (2016) and Andresen et al (2016). Andresen et al (2016) examined the root traits, growth and nutrition of several cultivars of onion (Allium cepa L.), spring wheat (Triticum aestivum L.) and lettuce (Lactuca sativa L.) grown in a low nutrient status soil.…”