Chickpea and white lupin rhizosphere carboxylates vary with soil properties and enhance phosphorus uptake

Erik Veneklaas, J. Stevens, Greg Cawthray, S. Turner, A. Grigg, Hans Lambers

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252 Citations (Scopus)


Chickpea and white lupin roots are able to exude large amounts of carboxylates, but the resulting concentrationsin the rhizosphere vary widely. We grew chickpea in pots in eleven different Western Australian soils, all withlow phosphorus concentrations. While final plant mass varied more than two-fold and phosphorus content almostfive-fold, there were only minor changes in root morphological traits that potentially enhance phosphorus uptake(e.g., the proportion of plant mass allocated to roots, or the length of roots per unit root mass). In contrast, theconcentration of carboxylates (mainly malonate, citrate and malate, extracted using a 0.2 mM CaCl2 solution)varied ten-fold (averaging 2.3 μmol g−1 dry rhizosphere soil, approximately equivalent to a soil solution concentrationof 23 mM). Plant phosphorus uptake was positively correlated with the concentration of carboxylates in therhizosphere, and it was consistently higher in soils with a smaller capacity to sorb phosphorus. Phosphorus contentwas not correlated with bicarbonate-extractable phosphorus or any other single soil trait. These results suggestthat exuded carboxylates increased the availability of phosphorus to the plant, however, the factors that affectedroot exudation rates are not known. When grown in the same six soils, three commonly used Western Australianchickpea cultivars had very similar rhizosphere carboxylate concentrations (extracted using a 0.2 mM CaCl2 solution),suggesting that there is little genetic variation for this trait in chickpea. Variation in the concentration ofcarboxylates in the rhizosphere of white lupin did not parallel that of chickpea across the six soils. However, inboth species the proportion of citrate decreased and that of malate increased at lower soil pH. We conclude thatpatterns of variation in root exudates need to be understood to optimise the use of this trait in enhancing cropphosphorus uptake.
Original languageEnglish
Pages (from-to)187-197
JournalPlant and Soil
Issue number1/2
Publication statusPublished - 2003


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