Growth, carboxylate exudates and nutrient dynamics in three herbaceous perennial plant species under low, moderate and high phosphorus supply

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    Abstract


    Background and aims
    Australian herbaceous native species have evolved in phosphorus (P) impoverished soils. Our objective was to explore shoot and root adaptations of two of these species with potential to be developed as pasture plants, at low, moderate and high P supply after 4 and 7 weeks of growth.
    Methods
    A glasshouse experiment examined the effect of 5, 20 and 80 mg P kg−1 air-dry soil on growth, rhizosphere carboxylate content, and mineral nutrition of two Australian native perennials, Kennedia nigricans (Fabaceae) and Ptilotus polystachyus (Amaranthaceae), and the exotic Medicago sativa (Fabaceae).
    Key results
    Leaf P concentrations at P80 were 6, 14 and 52 mg P g−1 leaf dry weight for M. sativa, K. nigricans and P. polystachyus, respectively. As soil P concentration increased, rhizosphere carboxylate content decreased for M. sativa, increased and then decreased for K. nigricans and was unchanged for P. polystachyus. For all species, the contribution of malic acid declined at the second harvest. For all species and P treatments, the amount of rhizosphere carboxylates per unit root length decreased as root length of a plant increased. Plant P content was determined more by P uptake rate per unit root length and time than by root length. Uptake of Mo for all species, and uptake of K, Mg and Mn for P. polystachyus, increased with soil P concentration. Uptake of Fe and S was higher when the content of carboxylates in the rhizosphere was higher.
    Conclusion
    Root physiological adaptations (i.e. rhizosphere carboxylate content and P-uptake rate) are more important than morphological adaptations (i.e. root length and diameter) to enhance the uptake of P and cations.
    Original languageEnglish
    Pages (from-to)105-117
    JournalPlant and Soil
    Volume358
    Issue number1-2
    Early online date10 Jun 2012
    DOIs
    Publication statusPublished - 1 Sept 2012

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