title: Rhizosphere Organic Anions Play a Minor Role in Improving Crop Species' Ability to Take Up Residual Phosphorus (P) in Agricultural Soils Low in P Availability.
abstract: Many arable lands have accumulated large reserves of residual phosphorus (P) and a relatively large proportion of soil P is less available for uptake by plants. Root released organic anions are widely documented as a key physiological strategy to enhance P availability, while limited information has been generated on the contribution of rhizosphere organic anions to P utilization by crops grown in agricultural soils that are low in available P and high in extractable Ca, Al, and Fe. We studied the role of rhizosphere organic anions in P uptake from residual P in four common cropsTriticum aestivum, Avena sativa, Solanum tuberosum, andBrassica napusin low- and high-P availability agricultural soils from long-term fertilization field trials in a mini-rhizotron experiment with four replications. Malate was generally the dominant organic anion. More rhizosphere citrate was detected in low P soils than in high P soil.B. napusshowed 74-103% increase of malate in low P loam, compared with clay loam.A. sativahad the greatest rhizosphere citrate concentration in all soils (5.3-15.2 μmol g-1root DW).A. sativaalso showed the highest level of root colonization by arbuscular mycorrhizal fungi (AMF; 36 and 40%), the greatest root mass ratio (0.51 and 0.66) in the low-P clay loam and loam respectively, and the greatest total P uptake (5.92 mg P/mini-rhizotron) in the low-P loam.B. napushad 15-44% more rhizosphere acid phosphatase (APase) activity, ~0.1-0.4 units lower rhizosphere pH than other species, the greatest increase in rhizosphere water-soluble P in the low-P soils, and the greatest total P uptake in the low-P clay loam. Shoot P content was mainly explained by rhizosphere APase activity, water-soluble P and pH within low P soils across species. Within species, P uptake was mainly linked to rhizosphere water soluble P, APase, and pH in low P soils. The effects of rhizosphere organic anions varied among species and they appeared to play minor roles in improving P availability and uptake.
authors.affiliation: Division of Biotechnology and Plant Health, Norwegian Institute of Bioeconomy ResearchÅs, Norway; Department of Environmental Sciences, Norwegian University of Life SciencesÅs, Norway.
authors.forename: Yanliang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Environmental Sciences, Norwegian University of Life Sciences Ås, Norway.
authors.forename: Tore
authors.initials: T
authors.lastname: Krogstad
authors.affiliation: Division of Biotechnology and Plant Health, Norwegian Institute of Bioeconomy Research Ås, Norway.
authors.forename: Jihong L
authors.initials: JL
authors.lastname: Clarke
authors.affiliation: Soil Biology Department, Institute of Soil Science and Land Evaluation, University of Hohenheim Stuttgart, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Hallama
authors.affiliation: Division of Environment and Natural Resources, Norwegian Institute of Bioeconomy Research Ås, Norway.
authors.forename: Anne F
authors.initials: AF
authors.lastname: Øgaard
authors.affiliation: Department of Environmental Sciences, Norwegian University of Life Sciences Ås, Norway.
authors.forename: Susanne
authors.initials: S
authors.lastname: Eich-Greatorex
authors.affiliation: Soil Biology Department, Institute of Soil Science and Land Evaluation, University of Hohenheim Stuttgart, Germany.
authors.forename: Ellen
authors.initials: E
authors.lastname: Kandeler
authors.affiliation: Division of Environment and Natural Resources, Norwegian Institute of Bioeconomy Research Ås, Norway.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Clarke
keywords: phosphorus; rhizosphere APase; rhizosphere organic anions; rhizosphere pH; rhizosphere water-soluble P