Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits.

Yan-Liang Wang,Anne Falk Øgaard,Nicholas Clarke,Marit Almvik,Susanne Eich-Greatorex,Jihong Liu Clarke,Tore Krogstad,Hans Lambers

doi:10.1093/aobpla/plv097

Abstract

Phosphorus (P) is an important element for crop productivity and is widely applied in fertilizers. Most P fertilizers applied to land are sorbed onto soil particles, so research on improving plant uptake of less easily available P is important. In the current study, we investigated the responses in root morphology and root-exuded organic acids (OAs) to low available P (1 μM P) and sufficient P (50 μM P) in barley, canola and micropropagated seedlings of potato-three important food crops with divergent root traits, using a hydroponic plant growth system. We hypothesized that the dicots canola and tuber-producing potato and the monocot barley would respond differently under various P availabilities. WinRHIZO and liquid chromatography triple quadrupole mass spectrometry results suggested that under low P availability, canola developed longer roots and exhibited the fastest root exudation rate for citric acid. Barley showed a reduction in root length and root surface area and an increase in root-exuded malic acid under low-P conditions. Potato exuded relatively small amounts of OAs under low P, while there was a marked increase in root tips. Based on the results, we conclude that different crops show divergent morphological and physiological responses to low P availability, having evolved specific traits of root morphology and root exudation that enhance their P-uptake capacity under low-P conditions. These results could underpin future efforts to improve P uptake of the three crops that are of importance for future sustainable crop production.

Highlights

Phosphorus (P) deficiency is one of the major limitations for crop productivity globally
Phosphorus was added as KH2PO4 in a concentration of 1 or 50 mM, designated as low P availability (P1) and P sufficient (P50), respectively
Our results showed no significant difference in citric acid exudation in barley between P-sufficient and P-deficient plants, but there was an increase in malic acid exudation in the P deficiency treatment (Fig. 4A, B and E), showing that there are differences in the types and quantities of organic acids (OAs) that are released from different crop species and varieties in response to P starvation

Summary

Introduction

Phosphorus (P) deficiency is one of the major limitations for crop productivity globally. Mineral P fertilizers are extensively used, and large economic benefits have been generated. P fertilizers have been added in amounts that far exceed the amount of P removed at harvest: up to 90 % of P applied as fertilizer may be strongly sorbed to the soil to become less available to plants, or eroded and lost in run-off Wang et al — Root morphology and exuded organic acid responses to low P availability et al 2013). It is important to understand P-acquisition mechanisms and genetically improve crop plants to be able to acquire P more efficiently, which would enable reduced P-fertilizer application

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