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Exudation of organic acids by Lupinus albus and Lupinus angustifolius as affected by phosphorus supply

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Abstract

In phytomining and phytoremediation research mixed cultures of bioenergy crops with legumes hold promise to enhance availability of trace metals and metalloids in the soil plant system. This is due to the ability of certain legumes to mobilize trace elements during acquisition of nutrients making these elements available for co-cultured species. The legumes achieve this element mobilization by exudating carboxylates and enzymes as well as by lowering the pH value in the rhizosphere. The aim of our research was to determine characteristics and differences in the exudation of Lupinus albus and Lupinus angustifolius regarding to quantitative as to qualitative aspects. Especially the affection by phosphorus (P) supply was a point of interest. Thus we conducted laboratory batch experiments, wherein the plants were grown over four weeks under controlled light, moisture and nutritional conditions on sand as substrate. Half of the plants were supplied with 12 mg P per kg substrate, the other half were cultivated under a total lack of P. After cultivation the plants were transferred from the cultivation substrate into a 0,05 mmol·L −1 CaCl 2 solution. After two hours the plants were removed, moist and dry mass off shoots and roots were measured together with the root length (Tennants' method). Concentrations of exudated carboxylates in the CaCl 2 solution were determined via IC (column: Metrosept OrganicAcids, eluent 0.5 mol·L −1 H 2 SO 4 + 15% acetone, pH=3; 0.5 mL·min −1). As a result four different organic acids were identified (citric acid, fumaric acid, tartaric acid, malic acid) in concentration ranges of 0.15 mg·L −1 (fumaric acid) to 9.21 mg·L −1 (citric acid). Lupinus angustifolius showed a higher exudation rate (in nmol per cm root length per hour) than Lupinus albus in the presence of phosphorus (e.g. regarding citric acid: 1.99 vs 0.64 nmol·(g·h) −1). However, as the root complexity and length of L. albus were far higher than of L. angustifolius, the total amount of exudated organic acids per plant of L. albus was higher than of L.angustifolius. Thus L.albus should be addressed as the more exudation effective plant in comparison to L.angustifolius (could be addressed as the more efficient one). Since organic acids in the rhizosphere of intermingling root systems of intercropped species play a key role during mobilization of trace metals our result clearly show that L.albus is most suitable for intercropping in a sense of phytoremediation and phytomining. These studies have been carried out in the framework of the PhytoGerm project financed by the Federal Ministry of Education and Research, Germany.
Geophysical Research Abstracts
Vol. 18, EGU2016-16986, 2016
EGU General Assembly 2016
© Author(s) 2016. CC Attribution 3.0 License.
Exudation of organic acids by Lupinus albus and Lupinus angustifolius as
affected by phosphorus supply
Werner Hentschel and Oliver Wiche
Technische Universität Bergakademie Freiberg, Germany (werner.hentschel@student.tu-freiberg.de)
In phytomining and phytoremediation research mixed cultures of bioenergy crops with legumes hold promise to
enhance availability of trace metals and metalloids in the soil plant system. This is due to the ability of certain
legumes to mobilize trace elements during acquisition of nutrients making these elements available for co-cultured
species. The legumes achieve this element mobilization by exudating carboxylates and enzymes as well as by
lowering the pH value in the rhizosphere.
The aim of our research was to determine characteristics and differences in the exudation of Lupinus albus and
Lupinus angustifolius regarding to quantitative as to qualitative aspects. Especially the affection by phosphorus (P)
supply was a point of interest. Thus we conducted laboratory batch experiments, wherein the plants were grown
over four weeks under controlled light, moisture and nutritional conditions on sand as substrate. Half of the plants
were supplied with 12 mg P per kg substrate, the other half were cultivated under a total lack of P.
After cultivation the plants were transferred from the cultivation substrate into a 0,05 mmol·L
1
CaCl
2
solution.
After two hours the plants were removed, moist and dry mass off shoots and roots were measured together with the
root length (Tennants’ method). Concentrations of exudated carboxylates in the CaCl
2
solution were determined
via IC (column: Metrosept OrganicAcids, eluent 0.5 mol·L
1
H
2
SO
4
+ 15% acetone, pH=3; 0.5 mL·min
1
).
As a result four different organic acids were identified (citric acid, fumaric acid, tartaric acid, malic acid) in con-
centration ranges of 0.15 mg·L
1
(fumaric acid) to 9.21 mg·L
1
(citric acid).
Lupinus angustifolius showed a higher exudation rate (in nmol per cm root length per hour) than Lupinus albus in
the presence of phosphorus (e.g. regarding citric acid: 1.99 vs 0.64 nmol·(g·h)
1
). However, as the root complexity
and length of L. albus were far higher than of L. angustifolius, the total amount of exudated organic acids per plant
of L. albus was higher than of L.angustifolius. Thus L.albus should be addressed as the more exudation effective
plant in comparison to L.angustifolius (could be addressed as the more efficient one). Since organic acids in the
rhizosphere of intermingling root systems of intercropped species play a key role during mobilization of trace
metals our result clearly show that L.albus is most suitable for intercropping in a sense of phytoremediation and
phytomining.
These studies have been carried out in the framework of the PhytoGerm project financed by the Federal Ministry
of Education and Research, Germany.
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